How to test a knock sensor - GM (low power condition)
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- Опубліковано 27 лип 2024
- GM 3100 engine, knock sensor test.
This engine had a slight rod knock or upper engine noise that was causing the knock sensor to record a false signal. The computers reaction was to retard ignition timing in an attempt to quiet the knock sensor down. The result was a severe low power condition at times.
The main take away with this case study is for low power complaints, don't forget to look at your knock sensor activity as a possible cause.
Engine Performance Diagnostics chapter 10 pages 6-7
Symptoms
- intermittent low power
- runs good cold and at WOT
- knock retard degrees on scan data goes very negative
Fix
- internal engine noise was causing false knock sensor activity
- left knock sensor disconnected (car was not worth repair cost to fix the engine)
Tests shown
- how to test a knock sensor
- how to determine the cause of a low power condition
Tools used
- scan tool
- labscope
- back-probing tools
Playlist
- (Chapters 9, 10 and 11) The 5v Reference and Signal Circuit Quick Tests
• (Chapters 9, 10 and 11...
Related Videos
- How to test a Knock Sensor (P0328) - Subaru
• How to test a Knock Se...
- How to test a Knock Sensor (P0328) - Nissan
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HI, HOW ARE YOU ALONG WITH YOUR FAMILY. HOPE EVERYONE IS WELL. AGAIN, YOU ARE BORN AS A GENIOUS. YOU PRESENTED YOUR CASE STUDY IN SUCH A COMPLETE AND DETAIL MANNER THAT COVERED ALL ISSUES WITH PERFECT TECHNICAL SUPPORT. YOU ARE OUR GREATEST ASSESTS OF THE INDUSTRY. I AM VERY GREATFUL TO YOU. MAY GOD BLESS AND YOUR FAMILY THANKS A MILLION FOR A GREAT DEDICATION.
BY THE WAY NO BODY HAS A CASE STUDY AS TECHNICALLY COMPLETED AS YOUR. POWER TO YOU.
Thank you so much!
your study cases and training are the best I have seen. I cannot thank you enough. the only thing I wish I came across your training and schooling a long time ago. God bless you.
Wow, thank you!
Yes, thank you very much! I'm happy I got your book to follow along and learn.
It starts at 12, goes through a 5v regulator (internal to the PCM) then is sent out to the sensor as a 5 volt bias. Some KS don't use this bias, some do. It is simply there for diagnostic purposes. In either case the KS produces an AC sign wave.
Thanks for the comment!
@@jedidiahwesley8522 it is pretty random and we are on to your bullshit spam, just know that every single fake name and account and the b.s. you guys are up to is being worked on behind the scenes to eliminate you.
Very nice. I really appreciate someone with obvious knowledge to go through this... even telling us about AC coupling! I'm dealing with a `99 TA LS1 that was just built; it has a PO327. It's stroked and cammed ....etc. I have a suspicion that I may have a clearance issue with one of the headers and one of the two knock sensors is picking it up as a knock. Time to break out my Tektronix scope!
Loop status with the engine cold may also be why the problem doesn't present itself while cold.
@skeeter5283 Engine noise, unplugged KS for her for now. It needs a new engine and we aren't going to fix it. She is going to drive it until it dies :)
Thanks for another good video. Very educational!
Well-described phenomenon. TY.
@fivefortyeye540i are you sure we are talking about the same thing? If you took it off that means you had the entire throttle body off. Its not that easy to remove. Most systems the throttle body is directly mounted to the intake with a gasket in between. On this one there is a small rubber boot connecting the two together. Look close.
@6:08 your knock sensor was 5v, when the knock sensor was unplugged you still got 5v, which means the wire to the sensor is good, but the resistor in the knock sensor is bad, otherwise that resistor would pull the 5v down to 1.5v. according to the little book you showed the resistor should have pulled the 5v down to 1.5v if it was plugged it, but it still showed 5v. i am at 6:20 and hit the pause button to say this. i will continue to watch and see if i am in error or not. i am not an expert, i am here trying to learn theory of operation, caught the over sight and thought i would share. i do thank you for this and all the videos of yours i have watched over the years
An engine with no spark advance will fire the plugs as the piston reaches TDC [top dead center] The normal procedure with vacuum or computer generated advance is to fire the spark plug some degrees Before top dead center to help warm up the engine and also to compensate for time needed for the spark flame to travel through out the cylinder. On some scanners the data PID value may be as much as 45 degrees of advance. The knock sensor does the opposite. It retards or reduces the amount of
Very informitive video !
I am troubleshooting a knock sensor problem with a Honda Aquatrax. It is nearly imposible to test this dynamically in the water as is the only time I get this issue. But, unfortunately, when the code pops, the computer throws the craft into limp mode. It is very aggrevating when you are very far away from shore. I have already installed a new knock sensor hoping the issue would go away, but the problem is still there. I am going to play with engine quieting tricks.
@assassinscov No plans as of right now. I'm still not confident enough with them to shoot that at this time. The heater circuit tests are identical but as far a pinpoint testing the signal wire(s) with a scope, it cannot be done with ease. The PCM monitors micro amp changes (not voltage) in the signal circuit to determine ratios. My test equipment will not read that low of amperage. So all testing is done with scan data only. I'll work on it. For book info. see my homepage for site
great video-----thanks
@JohnxWaynexGacy Good point thanks!
@fivefortyeye540i I thought you said fuel trim was high on both banks? If it was just the one bank there is also a timing chain problem to consider. I believe this engine has a primary and two secondary timing chains. So maybe the one bank the chain is off a tooth or two?
@fivefortyeye540i also when you smoke test this engine you need to completely block off the throttle body. This will put the intake under a slight pressure which will reveal any leaks easier.
@fivefortyeye540i ok, so no rubber boot in between then? The throttle body bolts directly to the manifold? Sorry for misleading you if that is the case.
I have a 2000 silverado with a 5.3. My SES light came on and i pulled the P0327 and P0332 knock sensor circuit low input codes and a B2S2 heater circuit codes so i replaced both knock sensors (the rear bank 2 sensor was completely corroded) harness, intake gaskets and b2s2 o2 sensor. Cleared the codes and truck ran fine til the next day SES came back with the knock sensor codes. I did the voltage test by hooking up my dmm and tapping on top of the intake valley cover and took an ohm reading. Both came back good so i checked for continuity on the harness and its good too. Any ideas on what the problem is? Truck really bogs down at wot and sucks gas. Thanks in advance.
Cool video, was there a problem with the sensors, or was it the engine noise issue causing then to falsely report to computer?
That is very enlightening, that if I had something stored in the engine bay vibrating on the block or maybe the head that it could be sending knock signals to retard timing. I never even considered that with all of my side experiments increasing mileage.
@ScannerDanner information, also all of my videos are embedded with my website address where my book is sold. Check it out. Thanks for you interest.
SUBSTANTIAL Sir ScannerDanner
Amazing tutorial thank you 👍
Sir ScannerDanner
From Nick Ayivor from London England UK 🇬🇧
i'm wondering... if there is a way to make those less sensitive and get them to produce less ac power to fool the computer. since this case, the engine is not pre detonating. and the pcm thinks it is due to piston slap, lifter slap or whatever the case is. i know that there is a bleed resistor inside the ks of if i remember right, 100 ohms, what if i would shove 12 volts on the lead wire to purpusly burn out the resistor inside. then install a resistor in serie to cut down the ac voltage coming from the ks, and in betwen that splice and the pcm, hook up a 100 ohm bleeder resistance to "indicate" the pcm pushing +5vdc that the ks is still pluggued in. reason for all of this is that i just done my 2 ks on my 5.3 2005 silverado, which are under the intake manifold. i've done the mistake of putting cheap ones, and well.. i have some lifter noise in my engine and i think its giving me the same problem as in the video. if i unplug my battery for a good 24 hours and plug it back, the truck runs wicked. i can stop on pavement, stromp the gas with no brakes and she'll burn 35x12 r18 tires.. a few drives later, she dosent even have enough power to make a brakestand. toughts anyone?
Hi Scannerdanner. I learn a lot from your videos as I'm new to a labscope but could I make a video request on wideband o2 sensors because I find it hard to diagnose these and think other viewers would benefit from it too? Also is this topic covered in your book and what's you web address where I can get a copy? Thanks for your hard work.
a friend has a very simular issue, was a lack of oil pressure, new oil pump fixed it, but depends how long it drove this way, with him he caught it right away
wouldn't you have to have the scope on ac voltage? instead of dc voltage?? I seen you turned ac coupling on to "block" the dc voltage so a knock sensor produces both ac/dc?? would you use ac coupling on speed sensors/ abs sensors??
@scannerdanner "computer is taking away 20 degree timing advance " dose that mean that there is no spark occurring 20 degree before tdc????
What should the ohms value be for a Vauxhall Zafira B 2008 1.6 petrol? Cant find anything in the Haynes manual or online. Thanks
ace video
In the page from the book its shows a 5volt feed to a resisture,wouldnt the 5volt be from the resisture ie the supply would be 12v dropping down to 5v to supply the sesnor?
Need to buy the book!
What should compression be on this engine? If timing has advanced a compression test would show higher then normal compression correct?
why not check resistance across the sensor for shorts?
i suspect the resistor in the sensor is bad, which is why the 5v circuit never drops down to 1.5 with the sensor plugged in. it was right there on the scope and he talked about it, but never zeroed in on it. i am here to learn, but i caught that right away. a resistance test would have likely shown an open circuit, or at least less resistance than it should with the resistor not working
I took it off and thoroughly inspected it, I put it back on smoked the the throttle down stream of Maf sensor smoke did come from top side of filter box wher it connects to cover air filter Now that u mentioned that agin I'm going to try to seal it of and see if that brings the numbers down..
@fivefortyeye540i Not sure, my diagnosis ended here. Too many miles to tear into this one, it wouldn't be worth it. Unplugged the K.S. and she is driving it until it dies.
Yes I blocked of throttle body with latex glove I put it over Maf sensor housing good positive pressure it inflated.. When I original took off intake manifold to replace pop off valve and put in new gasket... I only detached half the throttle body left other half
with intake
ScannerDanner, do you know if this is the case with a 5.3L Vortec like in a Siliverado 2000?
this has me thinking about glueing a knock sensor onto a long screwdriver then hooking that sensor to a scope and use the screwdriver for pinpointing engine noise like when you have a loud pulley or bearing and want to isolate where that sounds coming from.you could then touch the screwdriver to different suspect noisy parts,in theory the louder a pully the more you would see that on the scope and visa versa.
Ther was only a gasket thir for throttle body which I replaced.. This is a 98 Cadillac eldorado base model 4.6 litter.
Lifters or piston slap??
Isnt driving around without a knock sensor plugged in a good way to throw a rod?
You know what else Scannerdanner ther was no pcv valve in place for bank2 on valve cover. Back 1 has a pcv valve I don't know if this system calls for one or not
Hey quick question. I have a 2002 Camry Standard transmission that seems to have a slight knock. I performed the rod knock test with a rod in the spark plug hole while turning the crank to see if the was any play in any of the rod bearings but there wasn’t. What should I look for next? I’m terrified that it’s a main bearing
You have a knock in your engine? There is nothing I can help you with via the internet on that. I am sorry.
I think I have figured it out on the 4.6 I put new wires and plugs in. Since then i have been running the caddy on I off tring to figure out this lean condition.. So I went back pulled the plugs on bank 2 2plugs wher white (lean) and other 2 wher dark... Fuel delivery... Pulling injectors tonite....
Hi, nice video. Can knock sensor cause no start issue, by overfueling and wetting plugs causing not to start? My golf 1.4 tsi has no start issue, it has sparks, fuel, compression but doesn’t start. If I keep cranking , then compression goes down, and plugs are wet, and I can see fuel on top of piston. Changed plugs, coils, fuel pressure sensor, high pressure fuel pump, clean all grounds, changed camshaft sensor, fuel filter, replace fuses with brand new , but still no start. Nothing comes up when scanned in the engine module. I noticed that during cranking after 6-8 seconds red oil pressure light starts blinking. I have removed sump and checked oil pick up tube, but it was clean as new. I will change oil level sensor when putting back sump. I am totally lost,
There was another video I recently saw, which has no start issue and cranking fine. He changed everything on his bmw, but no success. Somebody told him to change oil level sensor and his car started. That’s my next step. Please help me resolve this issue, can been parked in driveway for over 4 months.
No, a knock sensor is not even used during cranking
timing needs to be verified, then check it for a plugged exhaust, (remove your upstream O2 and see if it will start)
I have a question. Can a bad knock sensor affect the timing? That is, in a vvt car, we could put the oscilloscope and it would show that the car is out of timing? But would the timing actually be correct?
No. Timing advance is limited when knocking occurs it does NOT change base relationships.
she needs to check the harmonic balancer. they will go and they will make noise like that.
Damn mani think that’s the same problem I have my knock sensors are working but I have loud lifter noise
I have a 3 wires knock sensor and the fed is getting 2.5 volts from the PCM, is that normal? I am having a very bad lack of performance.
I have a vw group car from 2003. The knock sensor has three wires. One for signal with 2.5 V. The other wires are for ground and shielding and both are connected to ground.
Yea Ltft are high on both banks I pulled bank 2 plugs because that bank was the hightest Ltft stft are normal after warm up on both banks
sir thank you but You don't upload any videos about bcm or airbag
When I see them I do, thanks!
Rod knock??
Dan, at the beginning of each video it would be nice to know the mileage ... what is the mileage?
+Ben quinn mileage doesn't dictate direction when troubleshooting, only after you find the problem do you then consider mileage for other recommended repairs.
I wonder what happened to that car.
This didn’t really help your was over explaining way to much.
sorry, I'm a teacher and I am teaching, not just showing the UA-cam world how to change a part
ScannerDanner nah it was awesome info but I was listening for one reason but you kept saying little extra stuff kept throwing me off. Other then that it was awesome info for sure just was throwing me for a loop
Thanks man, older video too. I've gotten a lot better, I think :-)
ScannerDanner I understood fine and I'm add. If your interested in mechanics you will learn.