I've never been so captivated by a single users videos before. This is outstanding! Where did you go to school at? Like I commented on another vid, your knowledge on SO MANY different systems, the test procedures, and CORRECT way to diagnose so many common problems is amazing. Kudos to you sir. You make what we both know is difficult, look incredibly easy.
here in the uk i work for vauxhall as a tech,that high pitched whistle could be the blocked cat or even the rocker cover baffle & sometimes the intake manifold itself!very informative video mann!
@buddiiee The restrictions in an exhaust system come from a melted and broken apart catalyst. The pieces of the cat can become trapped in the muffler too so at times the exhaust must be replaced from the cat. all the way back to the muffler. (including the cat. too of course). After the repairs the system should also be checked for a cause of the cat. failure. Its never good to just replace the cat. without checking for a cause.
@altlandf Not for a short test drive and I have done that before to test for a plugged exhaust. Your OBDII code reader should have some data PIDS you can look at, so if it does, then yes fuel trim can be seen with it. You are not using fuel trim to ID a plugged exhaust. Yes you can use a regular psi gauge, in fact I made my own adapter with an old O2 sensor and I use my cheep vacuum /psi gauge
Thats good enough, just wanted to make sure it wasn't dead before we continue. For your fuel pressure test (since it is the regulated type), disconnect the vac, hose and perform a WOT snap, pressure should not drop off during the test. As I just typed this....the regulator you mentioned may not be a regulator, it could be a pulsator with a vacuum hose on it. Which would make this a mechanical returnless system. They look like regulators. see if there is a return line on the rail
It pays to read other peoples comments in other videos because if I hadn't done just that while researching a P0420 code I wouldn't have read someones suggestion to get a free exhaust back-pressure check at Midas. This led me to ask YT for exhaust back-pressure test and thankfully I wound up here. Thanks very very very much for this 101 video and thanks for UA-cam for making it possible to post this valuable information. And I mean it sincerely!
had an 02 s10 last week same gauge you used pegged the gauge out at 2500 rpm! used your procedure as shown. except minus getting flipped off by people for holding traffic up...
Paul, very nice to test to get the right direction of diagnosis that is very important. I like when you prove your test not only one way but with two different ways. Looks like there are lots of cars going to fixed by me soon as I used to send them away. I don't see one video of yours that is not important to me. I am just scared, if I could accidently miss one to watch. I am alsot trying organize myself so that I wouldn't miss any.
@westin1985 the intent of this video is not about performance tuning it is simply how to recognize if your cat. is restricted. backpsi at idle should be zero. in fact backpsi under 3000 rpm in PARK (meaning no load) should be very near zero. reason being is in park there is not much throttle opening so the engine isn't breathing very much
Thank you very much for the positive feedback on the book. As far as a download, there isn't one however you can print from it and make your own paper version. Of course your access never expires either.
@spelunkerd Not sure about the alcohol content, but after a repair, I make sure fuel trim #s look normal under different loads, also that there is no misfire. Truthfully on the Impala and Monte Carlo, I have seen so many melted cats. and found no cause when I am done. I think it may be in the programming of the fuel curve?. Here in the aftermarket, we just put a new cat in it (factory cat of course) and if everything looks good we let it go.
Actually being you said that, your right there was no return line coming from it.. Well I'll see where I get tomorrow, Thanks again for your input and help man. I figured who else to go to with a confusing driveability issue than you. Have a good night!
That is strange, not sure I've seen that before. Lets not totally rule out fuel pressure here yet. Maybe it is borderline. Or maybe the MAF is dirty. Check MAF volts, it should go over 4v at WOT redline. Also check your fuel pressure on a WOT snap too. actually I think you can monitor fuel pressure on scan data on that system right. If so pull that PID up during your test drive too. Last question, are you sure the bank that is dropping lean has a functional O2 in it?
It certainly wouldn't be from a dirty MAF or fuel pressure problem as this would effect both banks. Do you have a car/truck that is doing that? Rich on one bank, and lean on the other at WOT?
Again thank you for your fast response. Actually yes, 98 Ford Taurus, 3.0 OHV engine, vacuum regulated fuel system. Fuel pressure was a little below spec. about 30 psi, but ran okay. (originally a no start and towed in) Both oxygen sensors switched good, but during WOT test, bank 2 went lean, although managed to run good. I did scope the fuel pump current which was around 4.5 amps but the waveform had a few spikes in it. Ran into the car at the end of the day so thats about all the info for now.
I didn't look at fuel trim closely for this one, but I know at idle and low speed they were in the normal range. Well at least normal enough for me to not look to closely. Also at WOT fuel trim is not relevant due to the O2 sensor being ignored and the system operating in open loop.
Other test methods: 1. use vacuum gauge (0,65 bar): § WOT : zero vacuum. § If restricted: 2000 RPM -> vacuum drops more and more 2. infrared thermometer test on cat (@ 2000 RPM, outlet 60° hotter than inlet) 3. scantool: 2nd O2-sensor steady voltage (±0,5V)
Double check that WOT O2 test for me. If you can, limit your data PIDs to just the two upstream O2s. This will allow for much faster data updates. Let me know the result
Can you tell us the main things you look for when examining an engine that comes in with a clogged cat? Does alcohol in gas cause that problem? If the engine is running fine with no misfires, is there anything else that you need to check for?
Robinson auto has a similar video regarding a bad cat due to a bad plug wire causing misfire, customer was driving for a while with the engine light on-- the plug wire was arcing on the engine, one thing causes a chain reaction
Mr. Danner, I have one for you. 03 ram 2500 5.7 Hemi. P0300. I just got my Launch X-431 V and I only barely know how to use it but the little bit I do know I'm questioning because the cat has been cut out and a pipe put in it's place. It's been that way for years so I know that's not the problem here but I don't know how o2 and fuel trim data will look. I had access to a ton of parts off a known good engine so I threw EVERYTHING at it, injectors with rail, plugs, wires, coils...needless to say...same issue. Not only is it a p0300 but it's got a flashing check engine light. The live misfire data shows most of the misfires on 2 and 3, opposite sides of the engine! I've been watching your videos and am starting to learn what a normal reading of short and long term fuel trim, o2 but now this thing has no cat. What happens to the downstream o2 sensor data....same as if it did have a cat? I'm jut guessing here but it seems like it would read exactly the same as the upstream o2 sensor. I put a vacuum gage on her and it actually reads in the "normal range" of the gage but it's very close to the "timing too late" or something to that effect. It's been a plow truck and race car hauler all it's life...maybe this is showing me I have my chain is too stretched and it's throwing random multiple misfire codes? I honestly barely know what to do with the scanner so any help you can offer would be greatly appreciated. Thanks in advance.
Love the vid. Our 13 expedition 5.4 3v. had a clogged cat. Dealer wanted to do all the work backwards. Tune up. Injectors. Ignition coils. Etc (out of warranty)$1400 before replacing the cat. (Still under warranty) After several meetings with mechanic and his stupidvisor, I them if they can find a problem after the cat was replaced then I will have it repaired. Finally got warranty cat replaced, and magically the car ran perfect. They couldn't find anything wrong. Wish I knew what caused it.
My reason for suspecting the catalytic converter... is I recently cleaned all the carbon off the intake manifold and throttle body. Most was wiped away, but obviously some went through the engine. I also used to have problems pulling grades when I bought the used truck. But it was 50-90% fixed when I replaced the plugs & cleaned the TB/MAFS/Intake. Putting my hand to the exhaust is sad. It's like a very light wind.
Hello Paul. I have question on this type of diagnostic using the o2 sensor data. Lets say you have a dual bank o2 sensor system and bank 1 (s1) reading is 800mv and bank 2 (s1) reading is 52mv at WOT. Would this indicate a fuel delivery issue? Would a MAF sensor problem cause both banks to be low? let me know when you get the chance. Thanks!
I did have the o2 sensors in the 2 graph mode on a snap-on solus and same results during multiple WOT drives. Would you recommend any other testing that would be a smarter approach to one lean bank situation? Otherwise I will can have more info tomorrow unless I figure it out. Thanks.
Thanks again Scanner and as always truly amazing! My daughters 05 Ford 500 will only run momentarily with the throttle on the floor. It has codes P2196 Oxygen sensor signal Biased stuck rich Bank 1 Sensor 1 and a P2198 which is the same code for Bank 2 sensor 1. It has 10.3 PSI Fuel rail pressure but since the O2's are showing rich perhaps this is the problem? I have 10 PSI at the fuel rail using live data at any RPM.. But it also has a P0191 Fuel Rail Pressure Sensor Circuit range performance code as well.
Sounds like sounds like a low volume fuel pressure to me. If fuel trims showing rich are you saying it negative fuel trims? If so then it's trying to add Fuel but can't because of low pressure. (Filter might be clogged) other rail pressure sensor is showing low because of not enough fuel I would bet
Would it hurt to run the vehicle with the 2 front O2 sensors removed? I have a OBD II code reader will this find a problem with the fuel trim? What should I look for? Would too much ethanol in the fuel melt the cats? In Pa right now there should be no more than 10% of that garbage in the gas. The 97 Explorer is NOT a flex fuel vehicle. The more ethanol the hotter the combustion gets. Anyway excellant video. Could you not use a regular psi guage?
So when you figure out your exhaust is clogged & it is most likely the CAT. What do you do? Grind off the pipe? weld on a universal cat? Where's the cheapest place to do this generally? My truck can't pull grades anymore. Codes I had = missfires, o2 heater, mafs, lean a/f, and more missfires. I checked/cleaned the plugs and wires. Good to go; got my engine power back & no more check engine light. But after getting warm (30minutes+ of driving)... I can't pull hills. Drops down to 50mph.
This ford has the vacuum regulated system so there wasn't anything in the scan data for the pressure. As for the o2 being functional, I didn't scope it, although I did watch scan data while unplugging the brake booster and drove the o2 lean and the response was great and it switches good around 2500 rpm along with bank 1.
no it is steps or counts on this design. No on question two, too many variables. I didn't notice or pay attention to map on this but yes map voltage being high would also help to id this condition.
would you consider to upload in the future a video how to test properly a cat inefficiency P0420 code, I have known It is very hard to make the call about replacing cats.they are very expensive some of them, I have clear the code and it has comes back after month when scoping front 02 and rear 02 I can see rear 02 does not follow pre cat switching also does not drop online after wot, post cat fall down after but still has the code, Also how do I scope or test on a/f ratio and post cat??P0420
The MAP voltage was the first thing I noticed as well. It is my understanding that the MAP voltage should be within about .2V of the TPS voltage. That sound right? It is also my understanding that the MAP could be high if the EGR is stuck open. Other indicators pointing to this would be a possibly high IAT reading and it would run funny at idle, but fine off idle. Does that sound right?
i love your video, i am actually on paid subscription . could you also instead of back pressure test test PIDS of dowstream O2 at 2500rpm, saw a video in which guy had bad cat and his B1S2 sensor at 2500rpm didn't have a flat line reading common on healty cat (usually close to 0.5V) but instead started following O2S1 sensor. Is that a good alternative test to prove cat is bad? To me seemed easier/faster method since he was watching on scan tools both upstream and dowstrem O2 sensors at 2500.
Remember a cat can be "bad" in two ways. 1. Lack of oxygen storage capability, but still provides good exhaust flow. 2. It is melted and restricting the exhaust. In both cases the downstream O2 will mimic the upstream So no, you cannot use a downstream O2 signal to determine if the exhaust is restricted. Great question and thank you for the subscription!
Awesome vid! I have an 05 Ford Escape that i just had 3 seperate exhaust leaks in 1 week. As fast as i repair 1, another starts...I am also getting a P405 EGR code? I checked EGR function and it seems to be fine. Now the truck has lost power and doesnt want to rev over 2500-3000rpm. It has 3 cats on it. 2 on the front manifolds and a rear cat. I can hear the rear cat sizzling inside of it. Is it possible the rear cat is breaking down, or is it coming from one of the front cats? No cat converter codes and both 02 sensors seem to be fluctuating quickly between .1V - .9V This vehicle for some reason doesnt have a sensor after the rear cat. So i cant monitor it... Was gonna just try and disconnect the rear cat at the flange and fire up the truck and see if it revs past 3000rpm. If it does, can i rule out a bad front cat? Also, where can i purchase a gauge for exhaust pressure? Thank you kindly!
depending on the set up, sometime s drilling a small hole in the exhaust is easiest. Of course removing the O2 and taking reading there works if you can get them out without ruining them. As for a back pressure gauge, I believe on one of my two tool pages I have one listed www.scannerdanner.com/tools.html www.amazon.com/shop/scannerdanner
In the begining, looking at the live data, the IAC position was 31. Is that number a duty cycle percentage? Can IAC numbers be an indication of exhaust restriction? Also i noticed MAP voltage was high, contradicting the low MAF Hz. If im not mistaken exhaust restriction reduces manifold vacuum?
What typically makes a catalytic converter go bad? Rich fuel would make it overheat and then melt. How does burnt oil effect them? Will anything else contaminate it and cause it not to function properly
Enjoy your vids although admittedly much goes way over my head. As a shade-tree, backyard mechanic that just wants to save some money by diagnosing and repairing my own cars, can you recommend a scanner that will do more than just read DTC's and live data? There are SO many different scanners with many different price points and, for me, confusing descriptions that I'll turn to you for expert for guidance. Thanks.
Paul - whats your thoughts on using an infrared thermometer to test for a clogged cat? I read that if the inlet temp is a few hundred degrees hotter than the outlet you have a restricted cat. However I'm not sure if you take your temp measurements at idle or 3000rpm. Your take?
You Have to be careful removing an o2 sensor i did once and the threads came off resulting in a new o2 sensor. I bought your book and i am loving it everyone buy his book its worth the money is it possible to down load the book or do we just keep the licence code for viewing purposes
What is the back pressure supposed to be at idle, 1,2,3,4, and 5 thousand rpm? If the car was on a dyno how much horse power is robbed from a restricted exhaust per psi of back pressure. There must be some formula that can approximate the horsepower it takes to move a volume of air at a certain psi.
Going to test my car with this very same method. Hopefully both of my cats are not clogged. But this is great start to not throw way a $1k in a pair of cats of not needed.
what if i remove the o2 sensor, start the engine, and then stick a rubber plug into the o2 hole see if i can hold it in?? and if i succeed to hold it in place into the hole then pressure is not too much and i know i'm good.. would that be a sufficient test to start with? thanks!!
I appreciate the video boss! Quick question for you though... if 1.5 - 2 psi at idle and 6 7 psi at 2500 rpm is high, what should the pressures actually be at?
My car is running a bit loud at idle and when I am in gear stopped at a light, the car randomly jerks/kicks back at me. Could this be a catalytic converter issue? My mechanic suggested this, but he said he really wasn't sure what it was and it was his best guess. 2006 DTS. I don't seem to have issues getting up to freeway speed like this impala in the video.
A narrow band O2 sensor is more of a switch. And can only indicate stoichiometric (lambda) which is 14.7:1 for gasoline. But yes, it is used for fuel control at steady throttle operation. Heavy accel or wide open throttle it is not used
Car went to 20mph a year ago and have been hesitant to tackle it, though I suspected exhaust. After watching this it doesn't look horrible to test before marching forward. Car apparently had a long term severe misfire, then with the help of a lumpy tire it suddenly acted up before we got it changed.
If you do not have a backpressure gauge, you can test drive it with the O2 removed and see if your power gets better. Don't drive it long this way, just one wide open throttle run to see.
@@ScannerDanner thank you, that's what I was planning originally, but I did go buy a gauge to check it right. It's just a junker car and maybe 4 years left before rust gets to something critical.
you sir would be describing fuel trims and would be correct on how fuel trims work to a point.. O2 voltage is the PID he was looking at on the scanner, high 02 voltage is rich low is lean....nice try.... looks like you need to attend rosedale.....LOL....nice and to the point DANNER nice work!!!.... man i need to buy your book
If you measure the MAP reading key on engine off? That will measure baro pressure. While at wide open throttle, if the MAP raises above baro? That will also identify a likely restricted cat. Although this test only works on non turbo vehicles.
had an impala with same motor. i replaced cats 2 times. had no power going up hill. got a tune up, and plugs had thick white crust on plugs. oh by the way i start rosedale may 27th.
+scannerdanner will you still get an acurate diagnosis of a restriction while brake torquing the engine? Another master tech showed me this tip and i was curious to know if he is correct or not.
+ScannerDanner right i understand that. But basically what i meant to ask is why do i get a different reading on a vacuum gauge when the vehicle is in park at 2-3k rpm vs when it is placed in gear at the same rpm. I have had vehicles test fine in park and some then drop to around 3-4 in. hg in gear.
load is much higher in gear, airflow is much higher in gear (when brake torquing and engine), so backpressure will be much higher too It is normal to have some backpressure under load, how much, is different on every car. So I don't use the test you are describing for that reason. It just adds another variable to the mix
+ScannerDanner gotcha. Thanks for clearing that up. I was thinking it was something along those lines but then that guy i spoke about said that's how he's always done it and I'm always up for learning bew methods. However, I learn with caution which is why i asked. Sounds like sticking with what i know will be best. Vacuum test in park, back pressure test, and pressure transducer if i can get ahold of one.
ScannerDanner, Thanks so much for this video man! You're a master of your craft 😎 Question if you'd be so kind: I have a 07' Frontier V6 with a P0300. New coils & plugs. Backpressure testing via O2 ports shows both driver side cats at 0 psi. Passenger front cat shows 3.5 psi, passenger rear shows 5 psi. Change the passenger front only? Or are they both shot? Not sure if the rear cat reading is somehow caused by a clogged front. Just don't want to waste $$$. Thanks for your time 🙂
So behind the cat you're showing 5 psi? This means pieces of the cat broke apart and are lodged somewhere downstream (resonator or muffler) Also you can't have a higher psi further down the exhaust, it's physically not possible. If you saw 5 psi downstream, you'd see that same 5 psi upstream. Is this a true dual exhaust system?
@@ScannerDanner @ScannerDanner Thanks so much for taking the time to reply! 👊 The system is a two-into-one. The layout on the passenger side is: Manifold to O2 Sensor, to Primary Cat, O2 Sensor, to Secondary Cat. All parts are in that specific sequence. I hope the way I wrote that helps. My bad if it doesn't. Gauge hookup at the first sensor bung reads 3.5 psi and 5 psi at that second sensor bung. Many thanks in advance 🙏
@@s.p.9582 you can't have a higher pressure downstream. Im not following your order, is the downstream O2 between the two cats? If so, your secondary cat is the problem and you will want to change them both anyway as they probably don't come separate and you definitely do not want to use aftermarket. In 2 months you will end up with a P0420 or P0430 code you won't be able to get rid of
@@ScannerDanner Once again thanks for your valuable time. I checked the pictures I took of the test gauge to confirm. Fwiw, I followed the instructions that came with the tester. Revs were at 2k. Engine was warmed. The downstream O2 is between the two cats. The upstream O2 is forward of the primary cat. Per the pictures, the downstream read 5.2 psi. The upstream read 3.8 psi. On the driver's side, readings at both ports were 0 psi (engine warmed, revs at 2k). Also, the cats are separate and can be installed individually. I really hope I don't have a bigger problem on my hands. This all happened a week before I was to sell the truck!! 😣 Current plan is to replace the problem cat(s) with a Walker EPA model. The truck is a 2007 Nissan Frontier V6 4WD with 90k miles. Many thanks in advance 🙏
@scannerdanner cool video... hey, I have an issue that happen almost from one day to the next... 2000 firebird 3.8 5 speed.... @ first I thought it was the clutch because I would feel the car "sit" every other shift or when I took it over three thousand rpms. the first time I noticed something off was when I floored it and saw smoke... which it was weird because my car does not smoke.... then days later, again but lingering smell of any kind, especially burned clutch, it a rich mixture. So that's why I'm with the idea that it is the clutch or slave cylinder, but every gear shifts with no issue, no grinding, my clutch pedal is high and reacts normal, no vibrations, no hydraulic leaks. now, talking about the catalytic converter there is no rotten egg smell but twice now I've heard backfiring more predominant as I coast to a stop light. I don't hear it as loud as usual and the power is not really there, I also notice that it idles higher than normal.... with that said, does it sound like a clutch issue, a catalytic issue or a vacuum issue.... thank you for your time..
I had this happen to me on a 01 Grand Prix 3.8 k engine. Same symptoms but bad misfiring on cylinder 3 and a little less on 1 and 4 under wot. Aftermarket Ngk spark plugs was my presumed culprit but changing them didn't fix it with wires. Cat measures 10 psi+ at wot. No bueno. I wish the exhaust would have whistled like this one did.
I have an '05 Cobalt that had misfires due to a bad/faulty Ignition Coil Module because it kept over heating because of the foam that sits on top of it that is glued underneath the beauty lid cover on the engine. After installing the ICM I cut away the foam that was suffocating/covering the ICM and preventing it's ventilation fins from performing their function and I also drilled ventilation holes through the plastic engine cover. I suppose the misfires and extra fuel can destroy or at the least shorten the catalytic converters life expectancy. In-credible.
Had a bad head gasket (bad head too, had to get a new one) but was burning a lot of coolant. Changed it, leak is gone but still lose power the longer I drive. Could burning coolant for a long time screw up my cat? Getting a pressure gauge to test for back pressure.
12 years later and this video is still relevant. Amazing in mastering the fundamentals
I've never been so captivated by a single users videos before. This is outstanding! Where did you go to school at? Like I commented on another vid, your knowledge on SO MANY different systems, the test procedures, and CORRECT way to diagnose so many common problems is amazing. Kudos to you sir. You make what we both know is difficult, look incredibly easy.
This video is perfect, short/sweat and to the point.
I think you mean sweet. Sweat is perspiration.
Wow i learned much more than diagnosing a clogging converter. TY for showing the scanner tool and all the values!
here in the uk i work for vauxhall as a tech,that high pitched whistle could be the blocked cat or even the rocker cover baffle & sometimes the intake manifold itself!very informative video mann!
@buddiiee The restrictions in an exhaust system come from a melted and broken apart catalyst. The pieces of the cat can become trapped in the muffler too so at times the exhaust must be replaced from the cat. all the way back to the muffler. (including the cat. too of course).
After the repairs the system should also be checked for a cause of the cat. failure. Its never good to just replace the cat. without checking for a cause.
Love the comments/pop-ups on the screen. Adding notes to my Engine perf. diag. book as I go. Love this channel!!!
Thank you!
@altlandf Not for a short test drive and I have done that before to test for a plugged exhaust.
Your OBDII code reader should have some data PIDS you can look at, so if it does, then yes fuel trim can be seen with it. You are not using fuel trim to ID a plugged exhaust.
Yes you can use a regular psi gauge, in fact I made my own adapter with an old O2 sensor and I use my cheep vacuum /psi gauge
Thats good enough, just wanted to make sure it wasn't dead before we continue. For your fuel pressure test (since it is the regulated type), disconnect the vac, hose and perform a WOT snap, pressure should not drop off during the test.
As I just typed this....the regulator you mentioned may not be a regulator, it could be a pulsator with a vacuum hose on it. Which would make this a mechanical returnless system. They look like regulators. see if there is a return line on the rail
It pays to read other peoples comments in other videos because if I hadn't done just that while researching a P0420 code I wouldn't have read someones suggestion to get a free exhaust back-pressure check at Midas. This led me to ask YT for exhaust back-pressure test and thankfully I wound up here. Thanks very very very much for this 101 video and thanks for UA-cam for making it possible to post this valuable information. And I mean it sincerely!
Just solved a problem thats had me in circles thank you
Ditto
had an 02 s10 last week same gauge you used pegged the gauge out at 2500 rpm! used your procedure as shown. except minus getting flipped off by people for holding traffic up...
Paul, very nice to test to get the right direction of diagnosis that is very important. I like when you prove your test not only one way but with two different ways. Looks like there are lots of cars going to fixed by me soon as I used to send them away. I don't see one video of yours that is not important to me. I am just scared, if I could accidently miss one to watch. I am alsot trying organize myself so that I wouldn't miss any.
@westin1985 the intent of this video is not about performance tuning it is simply how to recognize if your cat. is restricted. backpsi at idle should be zero. in fact backpsi under 3000 rpm in PARK (meaning no load) should be very near zero. reason being is in park there is not much throttle opening so the engine isn't breathing very much
Thank you very much for the positive feedback on the book. As far as a download, there isn't one however you can print from it and make your own paper version. Of course your access never expires either.
@spelunkerd Not sure about the alcohol content, but after a repair, I make sure fuel trim #s look normal under different loads, also that there is no misfire. Truthfully on the Impala and Monte Carlo, I have seen so many melted cats. and found no cause when I am done. I think it may be in the programming of the fuel curve?. Here in the aftermarket, we just put a new cat in it (factory cat of course) and if everything looks good we let it go.
Actually being you said that, your right there was no return line coming from it.. Well I'll see where I get tomorrow, Thanks again for your input and help man. I figured who else to go to with a confusing driveability issue than you. Have a good night!
thanks man! I really appreciate the support.
Great video and diag. Love when techs know there stuff
That is strange, not sure I've seen that before. Lets not totally rule out fuel pressure here yet. Maybe it is borderline. Or maybe the MAF is dirty. Check MAF volts, it should go over 4v at WOT redline. Also check your fuel pressure on a WOT snap too. actually I think you can monitor fuel pressure on scan data on that system right. If so pull that PID up during your test drive too.
Last question, are you sure the bank that is dropping lean has a functional O2 in it?
It certainly wouldn't be from a dirty MAF or fuel pressure problem as this would effect both banks. Do you have a car/truck that is doing that? Rich on one bank, and lean on the other at WOT?
Again thank you for your fast response. Actually yes, 98 Ford Taurus, 3.0 OHV engine, vacuum regulated fuel system. Fuel pressure was a little below spec. about 30 psi, but ran okay. (originally a no start and towed in) Both oxygen sensors switched good, but during WOT test, bank 2 went lean, although managed to run good. I did scope the fuel pump current which was around 4.5 amps but the waveform had a few spikes in it. Ran into the car at the end of the day so thats about all the info for now.
This video is straight-up brilliant
I didn't look at fuel trim closely for this one, but I know at idle and low speed they were in the normal range. Well at least normal enough for me to not look to closely. Also at WOT fuel trim is not relevant due to the O2 sensor being ignored and the system operating in open loop.
Other test methods:
1. use vacuum gauge (0,65 bar): § WOT : zero vacuum.
§ If restricted: 2000 RPM -> vacuum drops more and more
2. infrared thermometer test on cat (@ 2000 RPM, outlet 60° hotter than inlet)
3. scantool: 2nd O2-sensor steady voltage (±0,5V)
I dont understand. Theres not supposed to be vacuum at 2000 rpm and by vacuum drop do you mean pressure goes up or down?
Great tips , thanks !
Double check that WOT O2 test for me. If you can, limit your data PIDs to just the two upstream O2s. This will allow for much faster data updates. Let me know the result
thats awesome Richard! How did you find us and what helped you make this decision to come here?
yep. just make sure there are no 02 codes and exhaust leaks
Can you tell us the main things you look for when examining an engine that comes in with a clogged cat? Does alcohol in gas cause that problem? If the engine is running fine with no misfires, is there anything else that you need to check for?
Another great class Paul, always waiting for your videos to keep learning from your book, thank you..
Robinson auto has a similar video regarding a bad cat due to a bad plug wire causing misfire, customer was driving for a while with the engine light on-- the plug wire was arcing on the engine, one thing causes a chain reaction
Keep watching and keep learning thanks teacher
Mr. Danner, I have one for you. 03 ram 2500 5.7 Hemi. P0300. I just got my Launch X-431 V and I only barely know how to use it but the little bit I do know I'm questioning because the cat has been cut out and a pipe put in it's place. It's been that way for years so I know that's not the problem here but I don't know how o2 and fuel trim data will look. I had access to a ton of parts off a known good engine so I threw EVERYTHING at it, injectors with rail, plugs, wires, coils...needless to say...same issue. Not only is it a p0300 but it's got a flashing check engine light. The live misfire data shows most of the misfires on 2 and 3, opposite sides of the engine! I've been watching your videos and am starting to learn what a normal reading of short and long term fuel trim, o2 but now this thing has no cat. What happens to the downstream o2 sensor data....same as if it did have a cat? I'm jut guessing here but it seems like it would read exactly the same as the upstream o2 sensor. I put a vacuum gage on her and it actually reads in the "normal range" of the gage but it's very close to the "timing too late" or something to that effect. It's been a plow truck and race car hauler all it's life...maybe this is showing me I have my chain is too stretched and it's throwing random multiple misfire codes? I honestly barely know what to do with the scanner so any help you can offer would be greatly appreciated.
Thanks in advance.
Love the vid. Our 13 expedition 5.4 3v. had a clogged cat. Dealer wanted to do all the work backwards. Tune up. Injectors. Ignition coils. Etc (out of warranty)$1400 before replacing the cat. (Still under warranty)
After several meetings with mechanic and his stupidvisor, I them if they can find a problem after the cat was replaced then I will have it repaired. Finally got warranty cat replaced, and magically the car ran perfect. They couldn't find anything wrong.
Wish I knew what caused it.
Very helpful thank u for such a clear speaking to the point video
Love it, great troubleshooting process!
Thanks for this how to just diagnosed my 2004 malibu clogged cat!
My reason for suspecting the catalytic converter... is I recently cleaned all the carbon off the intake manifold and throttle body. Most was wiped away, but obviously some went through the engine.
I also used to have problems pulling grades when I bought the used truck. But it was 50-90% fixed when I replaced the plugs & cleaned the TB/MAFS/Intake. Putting my hand to the exhaust is sad. It's like a very light wind.
cool man, I look forward to meeting you.
@4:00 is perfection !
I bought your book. I like it. Very good information.
@CHIBA280CRV I was not involved in this car other than the diagnosis. The owner took the car elsewhere for the repair.
I have also bought this amazing book, the little that I translated into Spanish is excellent.
also published in Spanish
saludos desde LIMA - PERU
@westin1985 overly rich or lean ratios and misfiring, im sure oil burning doesn't help it either
Nice diagnostic walk through.
What is the normal reading for the exhaust back pressure should be ?
Thank you my friend!
Hello Paul. I have question on this type of diagnostic using the o2 sensor data. Lets say you have a dual bank o2 sensor system and bank 1 (s1) reading is 800mv and bank 2 (s1) reading is 52mv at WOT. Would this indicate a fuel delivery issue? Would a MAF sensor problem cause both banks to be low? let me know when you get the chance. Thanks!
I did have the o2 sensors in the 2 graph mode on a snap-on solus and same results during multiple WOT drives. Would you recommend any other testing that would be a smarter approach to one lean bank situation? Otherwise I will can have more info tomorrow unless I figure it out. Thanks.
master of knowledge
Thanks again Scanner and as always truly amazing!
My daughters 05 Ford 500 will only run momentarily with the throttle on the floor.
It has codes P2196 Oxygen sensor signal Biased stuck rich Bank 1 Sensor 1 and a P2198 which is the same code for Bank 2 sensor 1.
It has 10.3 PSI Fuel rail pressure but since the O2's are showing rich perhaps this is the problem?
I have 10 PSI at the fuel rail using live data at any RPM..
But it also has a P0191 Fuel Rail Pressure Sensor Circuit range performance code as well.
Sounds like sounds like a low volume fuel pressure to me. If fuel trims showing rich are you saying it negative fuel trims? If so then it's trying to add Fuel but can't because of low pressure. (Filter might be clogged) other rail pressure sensor is showing low because of not enough fuel I would bet
Thank you so much!
Would it hurt to run the vehicle with the 2 front O2 sensors removed? I have a OBD II code reader will this find a problem with the fuel trim? What should I look for? Would too much ethanol in the fuel melt the cats? In Pa right now there should be no more than 10% of that garbage in the gas. The 97 Explorer is NOT a flex fuel vehicle. The more ethanol the hotter the combustion gets. Anyway excellant video. Could you not use a regular psi guage?
Could you also test for reversion with a vacuum gauge
So when you figure out your exhaust is clogged & it is most likely the CAT. What do you do? Grind off the pipe? weld on a universal cat? Where's the cheapest place to do this generally?
My truck can't pull grades anymore. Codes I had = missfires, o2 heater, mafs, lean a/f, and more missfires. I checked/cleaned the plugs and wires. Good to go; got my engine power back & no more check engine light. But after getting warm (30minutes+ of driving)... I can't pull hills. Drops down to 50mph.
This ford has the vacuum regulated system so there wasn't anything in the scan data for the pressure. As for the o2 being functional, I didn't scope it, although I did watch scan data while unplugging the brake booster and drove the o2 lean and the response was great and it switches good around 2500 rpm along with bank 1.
Old, but still accurate. I just did a pressure test and the needle went half way on start up and when I pressed the pedal it pegged it immediately.
THANK YOU VERY MUCH FOR ALL THIS GREAT INFORMATION, GOD BLESS.
no it is steps or counts on this design. No on question two, too many variables.
I didn't notice or pay attention to map on this but yes map voltage being high would also help to id this condition.
Thank you, I'm so glad I finally watched your channel I definitely subsrcibed
Simple diag, great video😏
Thanks! 👍
Nice video. Very well done.
that was a very fast response, thanks so you mean if i have code P0420 can I relay on it replacing the cat. of couse if I do not have exhust leak??
would you consider to upload in the future a video how to test properly a cat inefficiency P0420 code, I have known It is very hard to make the call about replacing cats.they are very expensive some of them, I have clear the code and it has comes back after month when scoping front 02 and rear 02 I can see rear 02 does not follow pre cat switching also does not drop online after wot, post cat fall down after but still has the code, Also how do I scope or test on a/f ratio and post cat??P0420
What should the pressure reading be normally at idle and 3000 rpm?
The MAP voltage was the first thing I noticed as well. It is my understanding that the MAP voltage should be within about .2V of the TPS voltage. That sound right? It is also my understanding that the MAP could be high if the EGR is stuck open. Other indicators pointing to this would be a possibly high IAT reading and it would run funny at idle, but fine off idle. Does that sound right?
i love your video, i am actually on paid subscription . could you also instead of back pressure test test PIDS of dowstream O2 at 2500rpm, saw a video in which guy had bad cat and his B1S2 sensor at 2500rpm didn't have a flat line reading common on healty cat (usually close to 0.5V) but instead started following O2S1 sensor. Is that a good alternative test to prove cat is bad? To me seemed easier/faster method since he was watching on scan tools both upstream and dowstrem O2 sensors at 2500.
Remember a cat can be "bad" in two ways.
1. Lack of oxygen storage capability, but still provides good exhaust flow.
2. It is melted and restricting the exhaust.
In both cases the downstream O2 will mimic the upstream
So no, you cannot use a downstream O2 signal to determine if the exhaust is restricted.
Great question and thank you for the subscription!
Awesome vid!
I have an 05 Ford Escape that i just had 3 seperate exhaust leaks in 1 week. As fast as i repair 1, another starts...I am also getting a P405 EGR code? I checked EGR function and it seems to be fine.
Now the truck has lost power and doesnt want to rev over 2500-3000rpm. It has 3 cats on it. 2 on the front manifolds and a rear cat. I can hear the rear cat sizzling inside of it. Is it possible the rear cat is breaking down, or is it coming from one of the front cats? No cat converter codes and both 02 sensors seem to be fluctuating quickly between .1V - .9V
This vehicle for some reason doesnt have a sensor after the rear cat. So i cant monitor it...
Was gonna just try and disconnect the rear cat at the flange and fire up the truck and see if it revs past 3000rpm. If it does, can i rule out a bad front cat?
Also, where can i purchase a gauge for exhaust pressure?
Thank you kindly!
depending on the set up, sometime s drilling a small hole in the exhaust is easiest. Of course removing the O2 and taking reading there works if you can get them out without ruining them. As for a back pressure gauge, I believe on one of my two tool pages I have one listed
www.scannerdanner.com/tools.html
www.amazon.com/shop/scannerdanner
@@ScannerDanner thanks for the reply! Il have a look.
In the begining, looking at the live data, the IAC position was 31. Is that number a duty cycle percentage? Can IAC numbers be an indication of exhaust restriction? Also i noticed MAP voltage was high, contradicting the low MAF Hz. If im not mistaken exhaust restriction reduces manifold vacuum?
What typically makes a catalytic converter go bad? Rich fuel would make it overheat and then melt. How does burnt oil effect them? Will anything else contaminate it and cause it not to function properly
Great video. Helped out alot
Enjoy your vids although admittedly much goes way over my head. As a shade-tree, backyard mechanic that just wants to save some money by diagnosing and repairing my own cars, can you recommend a scanner that will do more than just read DTC's and live data? There are SO many different scanners with many different price points and, for me, confusing descriptions that I'll turn to you for expert for guidance. Thanks.
I forgot to say, I CAN'T spend $2-300 on one.
Post this to my forum. It is free to join and you can gain insight on what others are using. www.scannerdanner.com/forum.html
Paul - whats your thoughts on using an infrared thermometer to test for a clogged cat? I read that if the inlet temp is a few hundred degrees hotter than the outlet you have a restricted cat. However I'm not sure if you take your temp measurements at idle or 3000rpm. Your take?
You Have to be careful removing an o2 sensor i did once and the threads came off resulting in a new o2 sensor.
I bought your book and i am loving it everyone buy his book its worth the money is it possible to down load the book or do we just keep the licence code for viewing purposes
What is the back pressure supposed to be at idle, 1,2,3,4, and 5 thousand rpm? If the car was on a dyno how much horse power is robbed from a restricted exhaust per psi of back pressure. There must be some formula that can approximate the horsepower it takes to move a volume of air at a certain psi.
great video my friend
factory only! more than likely an aftermarket cat. (even direct fit) will set another cat. code within a few months.
a psi rise in the exhaust and intake
great video man ..
Gauge and adapter is from where? I guess you could use a compression/leakdown setup with a low pressure gauge?
Not sure? I'm sorry, but I do have one listed on my Amazon Affiliate page www.amazon.com/shop/scannerdanner
Going to test my car with this very same method. Hopefully both of my cats are not clogged. But this is great start to not throw way a $1k in a pair of cats of not needed.
what if i remove the o2 sensor, start the engine, and then stick a rubber plug into the o2 hole see if i can hold it in?? and if i succeed to hold it in place into the hole then pressure is not too much and i know i'm good.. would that be a sufficient test to start with? thanks!!
I appreciate the video boss! Quick question for you though... if 1.5 - 2 psi at idle and 6 7 psi at 2500 rpm is high, what should the pressures actually be at?
Near 0 for this test
Love this Video
My car is running a bit loud at idle and when I am in gear stopped at a light, the car randomly jerks/kicks back at me. Could this be a catalytic converter issue? My mechanic suggested this, but he said he really wasn't sure what it was and it was his best guess. 2006 DTS. I don't seem to have issues getting up to freeway speed like this impala in the video.
So the o2 readings are only used to tell the condition of rich/lean condition & not use it to control the A/F ratio correct?
A narrow band O2 sensor is more of a switch. And can only indicate stoichiometric (lambda) which is 14.7:1 for gasoline.
But yes, it is used for fuel control at steady throttle operation. Heavy accel or wide open throttle it is not used
@@ScannerDannergot it thank you
Car went to 20mph a year ago and have been hesitant to tackle it, though I suspected exhaust. After watching this it doesn't look horrible to test before marching forward. Car apparently had a long term severe misfire, then with the help of a lumpy tire it suddenly acted up before we got it changed.
If you do not have a backpressure gauge, you can test drive it with the O2 removed and see if your power gets better. Don't drive it long this way, just one wide open throttle run to see.
@@ScannerDanner thank you, that's what I was planning originally, but I did go buy a gauge to check it right. It's just a junker car and maybe 4 years left before rust gets to something critical.
you sir would be describing fuel trims and would be correct on how fuel trims work to a point.. O2 voltage is the PID he was looking at on the scanner, high 02 voltage is rich low is lean....nice try.... looks like you need to attend rosedale.....LOL....nice and to the point DANNER nice work!!!.... man i need to buy your book
How much was. That scanner& where'd you get it
If you measure the MAP reading key on engine off? That will measure baro pressure. While at wide open throttle, if the MAP raises above baro? That will also identify a likely restricted cat. Although this test only works on non turbo vehicles.
amazing :D from Peru
had an impala with same motor. i replaced cats 2 times. had no power going up hill. got a tune up, and plugs had thick white crust on plugs. oh by the way i start rosedale may 27th.
+scannerdanner will you still get an acurate diagnosis of a restriction while brake torquing the engine? Another master tech showed me this tip and i was curious to know if he is correct or not.
you don't need to and it's bad for the torque converter to do that for more than a few seconds.
+ScannerDanner right i understand that. But basically what i meant to ask is why do i get a different reading on a vacuum gauge when the vehicle is in park at 2-3k rpm vs when it is placed in gear at the same rpm. I have had vehicles test fine in park and some then drop to around 3-4 in. hg in gear.
load is much higher in gear, airflow is much higher in gear (when brake torquing and engine), so backpressure will be much higher too
It is normal to have some backpressure under load, how much, is different on every car. So I don't use the test you are describing for that reason. It just adds another variable to the mix
+ScannerDanner gotcha. Thanks for clearing that up. I was thinking it was something along those lines but then that guy i spoke about said that's how he's always done it and I'm always up for learning bew methods. However, I learn with caution which is why i asked. Sounds like sticking with what i know will be best. Vacuum test in park, back pressure test, and pressure transducer if i can get ahold of one.
it is actually very simple. use a factory cat. only! aftermarket cats will continue to set P0420 codes
ScannerDanner, Thanks so much for this video man! You're a master of your craft 😎 Question if you'd be so kind: I have a 07' Frontier V6 with a P0300. New coils & plugs. Backpressure testing via O2 ports shows both driver side cats at 0 psi. Passenger front cat shows 3.5 psi, passenger rear shows 5 psi. Change the passenger front only? Or are they both shot? Not sure if the rear cat reading is somehow caused by a clogged front. Just don't want to waste $$$. Thanks for your time 🙂
So behind the cat you're showing 5 psi? This means pieces of the cat broke apart and are lodged somewhere downstream (resonator or muffler)
Also you can't have a higher psi further down the exhaust, it's physically not possible. If you saw 5 psi downstream, you'd see that same 5 psi upstream. Is this a true dual exhaust system?
@@ScannerDanner @ScannerDanner Thanks so much for taking the time to reply! 👊
The system is a two-into-one. The layout on the passenger side is: Manifold to O2 Sensor, to Primary Cat, O2 Sensor, to Secondary Cat. All parts are in that specific sequence. I hope the way I wrote that helps. My bad if it doesn't.
Gauge hookup at the first sensor bung reads 3.5 psi and 5 psi at that second sensor bung. Many thanks in advance 🙏
@@s.p.9582 you can't have a higher pressure downstream. Im not following your order, is the downstream O2 between the two cats? If so, your secondary cat is the problem and you will want to change them both anyway as they probably don't come separate and you definitely do not want to use aftermarket. In 2 months you will end up with a P0420 or P0430 code you won't be able to get rid of
@@ScannerDanner Once again thanks for your valuable time. I checked the pictures I took of the test gauge to confirm. Fwiw, I followed the instructions that came with the tester. Revs were at 2k. Engine was warmed.
The downstream O2 is between the two cats. The upstream O2 is forward of the primary cat. Per the pictures, the downstream read 5.2 psi. The upstream read 3.8 psi. On the driver's side, readings at both ports were 0 psi (engine warmed, revs at 2k).
Also, the cats are separate and can be installed individually. I really hope I don't have a bigger problem on my hands. This all happened a week before I was to sell the truck!! 😣 Current plan is to replace the problem cat(s) with a Walker EPA model.
The truck is a 2007 Nissan Frontier V6 4WD with 90k miles. Many thanks in advance 🙏
@@ScannerDanner I hope all is well. So, based on my last message, just get the secondary cat for now?
@scannerdanner
cool video... hey, I have an issue that happen almost from one day to the next... 2000 firebird 3.8 5 speed.... @ first I thought it was the clutch because I would feel the car "sit" every other shift or when I took it over three thousand rpms. the first time I noticed something off was when I floored it and saw smoke... which it was weird because my car does not smoke.... then days later, again but lingering smell of any kind, especially burned clutch, it a rich mixture. So that's why I'm with the idea that it is the clutch or slave cylinder, but every gear shifts with no issue, no grinding, my clutch pedal is high and reacts normal, no vibrations, no hydraulic leaks. now, talking about the catalytic converter there is no rotten egg smell but twice now I've heard backfiring more predominant as I coast to a stop light. I don't hear it as loud as usual and the power is not really there, I also notice that it idles higher than normal....
with that said, does it sound like a clutch issue, a catalytic issue or a vacuum issue.... thank you for your time..
I had this happen to me on a 01 Grand Prix 3.8 k engine. Same symptoms but bad misfiring on cylinder 3 and a little less on 1 and 4 under wot. Aftermarket Ngk spark plugs was my presumed culprit but changing them didn't fix it with wires. Cat measures 10 psi+ at wot. No bueno. I wish the exhaust would have whistled like this one did.
I have an '05 Cobalt that had misfires due to a bad/faulty Ignition Coil Module because it kept over heating because of the foam that sits on top of it that is glued underneath the beauty lid cover on the engine. After installing the ICM I cut away the foam that was suffocating/covering the ICM and preventing it's ventilation fins from performing their function and I also drilled ventilation holes through the plastic engine cover. I suppose the misfires and extra fuel can destroy or at the least shorten the catalytic converters life expectancy. In-credible.
How does a 2003 OBD II car only have a single upstream O2?
What causes the whistle? I have the same thing going on with my 02 Nissan Frontier SC
Had a bad head gasket (bad head too, had to get a new one) but was burning a lot of coolant. Changed it, leak is gone but still lose power the longer I drive. Could burning coolant for a long time screw up my cat? Getting a pressure gauge to test for back pressure.
sure, because it will mess up the AF Ratio