Jeep CJ Fuel and Temperature Gauge Problems and Testing
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- Опубліковано 23 січ 2022
- The AMC Jeep CJs fuel and temp gauges are notorious for not working. Most of the time it's because they have burned up due to a bad or corroded ground. But I'm willing to bet that a lot more of these gauges are still good and just need to be tested to see where the real problem is. In this video we go through and test the Ohm ranges for both the fuel and temperature gauges and the specs that they should be within to be accurate and functional. We also talk about what each connector does and how to test to see if you are getting a signal or voltage.
Tools you'll need:
Gator clip test wires
Voltmeter with continuity, ohms, and DC current settings
12 volt battery (car battery)
Power test light
Fuel Sending Unit: www.mtscompany.com/
Wire diagram for subscribers: dellis6914@gmail.com - Авто та транспорт
Thanks for everything. Over the past two years restoring my 79 cj5 I have gone from clueless to mildly competent thanks largely to your great videos. My daughter will be driving in a year and she wants the jeep. It is you that is giving it to her
I’m just the messenger. You’re doing the work :) she’s a lucky kid.
Mines hasn't worked in 8 years. This video will help me get mine working. Thanks for your help.
Please report back what you find out.
A friend of mine ask me to watch this video and this is the best quick test of the OEM fuel gauge. Using the test light is the best way to run a quick test of the fuel gauge. I've been seeing more and more of you videos pop up and really like them.
Any opportunity that you have to add to the knowledge base of the small following that I have, please do so.
What a cool and helpful guy you are! My better half rolls her eyes every time I add another piece of blue tape with the new "do not exceed" mileage to the speedo. You've taught me now how to properly diagnose this. If I do trace it to the sending unit, that blue tape method might just have to be the solution though with so many rusty bolts attaching the skid plate to the gas tank!
Is your skid plate rusted out or is it just the bolts? I have a video on how to remove the skid plate that might be helpful. And I might have a skid plate I could help you with. If you fix this, or find what the problem is, you're going to be a lot more confident in your range :) Plus you can use your blue tape for actual home improvement.
I guess I'm one of the lucky few that all of my gauges work when I found my 77 CJ7. I now daily drive it after a few years of restoring it. I love it!
Yes. Yes you are. Lucky to have a 77 CJ7. Lucky to have all the gauges working. :) How far along are you in your restoration?
Just watched video , excellent , ALL your videos are super gelpful. You are right to the point and explain it step by step . I use your videos all the time and very helpful. .
Glad to help.
this video rocks. helped me solve my fuel gauge issues. realized that my original sender hasn't been grounded due to a change to rubber fuel lines. now i just have to figure out how to add a ground....
Well you’re 98% of the way there.
Thanks for the help learned a lot from you now my oem gauge’s working after 30 plus years right on
Ps need more cool guy videos
Great video. Great troubleshooting so much better than just throwing parts at it
We all throw enough money at our CJs, so anywhere we can save the original stuff is smart.
Nice detail, thank you!
Happy New Year ! Oh and yes , cool sweater 👍 . I’ll say I jumped the gun as I put myself in the position that time was of the essence .
Not a smart thing to do on my part , but consider the source 🙃 . If I had actually physically inspected a bit more , I would have found road dirt and corrosion on a rear harness disconnect by the left rear tail light and maybe the original gauge may have worked and possibly been fairly accurate ? Well , I opted to replace both cluster gauges , fuel and temperature since I wasn’t getting a reading on either .
I did have voltage but decided to pull the trigger anyway . Being of sound mind and somewhat of body , I pulled the tank and reinstalled it with a new sending unit . That proved to be a necessity . Plenty of corrosion and not a lick of ground . The sending unit was worse for wear and didn’t give such a clean response on its scale on the ohm gauge . I may have screwed the pooch with the dash gauge as both gauges did ohm out fair . It would have proved interesting using an OMIX Ada sending unit with an OEM 5 volt fuel gauge . Accuracy is questionable so I’m always asking myself how much gas do I think is really in . As far as the gauge working , if I remember , the temp gauge pegged and I had to reverse the polarity by reversing the jumper connection . It’s actually a year and a half ago I did the job but I’m reasonably sure it was the temp gauge and not the fuel gauge that had the polarity problem . OMIX Ada tech was very helpful and was aware of then manufacture problem . They graciously offered to replace if was found a problem . Once the polarity was reversed , all was well . Can I say the temp gauge is accurate ? Well , looking at the scale which just has a C and an H and a line in between , it’s old school all over again. No digital so no accuracy in that respect . As you note in the video , make,darn sure to find that connection and clean it if hounding to get a proper signal to / from the sending unit . Of course we would 😊 . Will I venture to drop the tank and experiment with the sending unit for accuracy ? I’ve been meaning to . There were better mopar units , fuel and temp but I don’t think as of this date are available . Not cool but just typical .
I've lost track of how many pieces I've done that exact same thing with. There's something about the urgency of restoring these CJs that get the best of us. For example I had a problem with my AMC 20 brake backing plate. I found a local AMC 20 with N stamped in the housing. 3.54 gears with Trac Lok! I get it home take it apart at the same time I take my original AMC 20 apart. I come to find that the original AMC 20 was N stamped and the exact same. I spent $150 and $90 in rebuild kits and got nowhere. Meh.
I accidently put the hot wire in the jumper piece (A) and now my gauges need to be replaces :( , Cool guy thank you for your videos it makes life easier!
Major bummer. I actually did the same thing about a year ago before I learned the right way to do it. Wish I could’ve saved your gauges for you :(
@@coolguy_CJ7 your already saving us a lot with your videos!
Thanks so much for the video it helped me out a lot.
I sure it didn't fix everything, but at least it's a start.
A very very nice car, from bottom to top, inside out, clean and shine..👍🏼👍🏼👍🏼
Labor of love…
Thanks for the video, very helpful since I've been procrastinating on checking my fuel guage and sending unit. I'll fill the tank until fuel spills out but the needle never gets all the way to the right/full side. Then I'll drive it until it reads empty but keeps on running for several more days. I know the 15 gallon tank was replaced with another 15 about two years ago but I'm not sure about the sending unit or the gauge...I think they are still original.
Only one way to find out where the problem is..... :)
Very helpful! Thank you!
Glad to help.
Nice Golden Eagle
Good video. I have 2 driveable cj5. They both have problems with the gauges
Let me know if this video help out. There’s always an answer, sometimes it just hidden really deep.
@@coolguy_CJ7 yes this video was helpfull. I haven't tried diagnosing the gauges I've only messed with the sending units. I have new factory gauges not installed. I gave up not sure I could install them in the 1971 Speedo. I keep track of my mileage for the fuel and I keep good hoses for the cooling. I.always think I'll get it someday. The temp is the only thing that makes me a little nervous. My factory 1977 gauges made it about 275 000 so they did ok. They both went out at the exact same time with the temp sometimes coming on with a reading and sometimes not. I didn't know anyone on the planet had a working set but I guess you do. I was impressed with your video. It makes me want to play with them again. Your leading me thru the diagnoses will help me pay attention to the factory manual which on this I have not done well. Thank you very much.
Good video, but a couple of things, you need to hand adjust your sending unit on the bench before installing it, by bending the arm. The sending unit is rarely correct from any manufacturer (legally they cant be) unless its oem . This is done by using your ohm meter and testing it at empty versus full, you will need the shop manual to get the correct resistance at the desired level (61 ohms empty, 23 ohms half tank, 10.3 full for 1981). If your still not getting the desired reading on the gauge you will need to remove the gauge from the housing, use alligator leads to make the connection and in the middle of the gauge back side there's a tiny hole with an adjuster screw which will allow you to dial it in, flat tip screw driver.
Great build. I didn't want to get into that much detail just yet. In a future video I'm going to take that speedometer part and open up the gauges to show what they are made of and how they work.
@@coolguy_CJ7 Good plan, so many jeepers struggle with the gas gauge just because they assume out of the box (Sending unit) its ready to go, not realizing it needs to be set up before use. By the way nice CJ7, very clean
Again thank you
Glad to help.
Been looking forward for this one! My 75 gas gauge is reversed,full on left, and empty on the right,guess that’s a 75 and earlier model thing?
Yes. AMC made the 75-77 CJ 5 a transition period and changed a lot of things. Your gauge/speedometer should still have the markings on the back though.
Great video! I just picked up an '83 CJ-7, and the speedometer works, but the temp and fuel gauges, along with the lights, do not work. I haven't tested the connections yet or taken apart the dash.
I really need to do a video on the dash wire harness. Just need to get some time to do it. :)
I bought a crown coolant sending unit. It was doa. Bought a amazon mexican made one and it seems to work fine. Idk what brand fuel sending unit i have but its aftermarket and works. I have the original, but replaced it when my old gas tank rotted out. Dirt tends to sit in between the skidplate and rust from the outside in.
That's part of the difficulty with restoring these old AMC vehicles. There's only so many companies out there that are willing to put the effort into making the replacement parts. They seem to be from low manufacturing standard countries at the cheapest price. Annoying when you're trying to make things right.
Also, that's why I powder coated my skidplate :)
Hi. Really good video. I am about to replace My cj5 77 fuel gauge. It's better and safetier to work with all the things out of the car (over a table). Thank you
Definitely. Testing the gauges while still in the CJ is really difficult. :)
Reach out if you have any questions on the new gauge. Do you kind of I ask what you are replacing it with?
On my ‘77 CJ resto, swapped sending unit with a crown and it was DOA. Swapped for a different one and it worked. Now 6mo later it still works, but may or may not got the FULL when I top tank off. :(
I'd bet that the sending unit works, but only so much. The regulator is probably not good and you only get a limited amount of signal from the sending unit. Or you have a corroded connection/bad ground somewhere in the wire.
@@coolguy_CJ7 Thanks! I'll check that out.
Hey bud, like all your videos. I have a 86 cj7 with some really screwed up wiring. All my exterior lights work as they should but no dash lights at night, also the last guy that owned this jeep, replaced the speedometer. Did not connect anything to it but had installed a separate gas gauge, that does work. I noticed I don’t have the jumper wire from A to temp gauge on this. Is the new ones different or do you know ? and also my ohm readings were very different than yours. Any thoughts? Thanks for any help. Also you would not have any diagrams of the light switch by chance would you?
Email me at dellis6914@gmail.com and I’ll send you what I have.
Does your voltmeter function? I disassembled mine and have noticed then when I hooked to my power supply that the magnet does move and the needle is not fixed to it, I was wondering if it originally was and if a small dot of superglue could solve the issue. Any feedback would be great, love your channel I bought my 81 cj last March and am loving it!
The one in the dash? Yes. I've taken apart a few of these gauges to see how they work and have found that the most fragile of the group is the voltmeter. The needle is brittle, fragile plastic and breaks off at the slightest touch. You could try glue but be very careful and use a very light touch. There are plenty of people selling good used voltmeters on FB marketplace. Don't pay more than $30 for one though :)
Great video as usual! Also, very timely. I’m just putting the dash back in my 1976 CJ7 and had the speedometer installed. I took it out to do these tests just to be sure the gauges are good. So, I am getting all of the correct Ohm readings from the fuel and temp gauges. I also did the 12v battery test and both gauges take power. But, when I tested for continuity between the fuel gauge “I” post and the speedometer housing I don’t get a tone. Is there a way to check the ground or clean the contacts? Any help is really appreciated!
Have you opened up the speedometer and taken apart the housing? There is a small metal strap on the back of the fuel gauge that grounds it into the speedometer housing. Start with taking the cardboard piece of the back and check for corrosion/rust.
I actually have the same exact problem. So I took apart my cluster and pulled out the fuel gauge pod. The little ground tabs on the back of the gauge look ok but I cleaned them anyway along with the “I” post. Reassembled and still no continuity between the I post and housing. But if I test continuity between the I post and the grounding tabs on the fuel gauge, there is also nothing. So maybe a bad gauge? I have a Chinese cluster from quadratrac and I pulled the fuel gauge pod out of there and put it in my cluster and I have proper ground continuity. Ugh. Any thoughts?
Also, if there was continuity between the post with voltage and the cluster case, wouldn’t that create a short?
Great video I just picked up my first jeep at 60yrs young had mostly muscle cars through my years you said you have a wiring diagram for the 79 CJ7 which is what I just purchased and look forward to many of your videos to come I don’t see an email address to send to you my request for it. Can you tell me how to get in touch with you? 🙏🏻
Should be in the description of the video. Dellis6914@gmail.com
Hey. Pretty good video! Question for ya…..
With my ACC on, I tested the wire in the engine compartment going to my temp sensor. Mine is a constant light and not flashing. Thoughts on this?
Sounds like the sensor is bad. Let me check my documentation tonight to confirm.
@@coolguy_CJ7 ok, so here’s where I’m at…..
Purple wire in engine compartment does pulse with test light. With the constant power before the engine was on accessory. So in run it’s good to go.
Tested temp gauge with constant 12v as indicated in your video. It works. Terminal in the back also has pulsing power.
However, the gauge is not working with it assembled and connected. I made a dedicated ground wire for the speedo cluster too.
Thoughts?
i usually just count KM. can get ~250 km to a full tank but driving over bridges etc gets scary when the gauge is at 0. maybe when i get the time i'll try out your tips thanks
No time better than the now. Although the guessing game that you go through makes the CJ drive that much more adventuresome. :)
Where do you get all your Cj parts at? Ive receive my dad’s old 86 Cj, and i REALLY wanna fix her up although 20 years of Florida humidity ruined a lot.
Kind of a mixed bag. Most gaskets and maintenance type pieces, I use Rock Auto, Morris 4X4, and Quadratec.
Then there are the hard to find things, like the power brake booster dust boot or the reverse light switch. NAPA seems to have a lot of these.
If you want to go OEM, then FB Marketplace (random pricing), eBay (stupid expensive) or reach out to Ray Moulton at Deadjeep.com. He is the best in the business and killer with prices. Great guy to boot.
I had an omix dead on arrival… the post was grounding out on the housing… only has a tiny cheap little oring isolator… was bad. Second replacement unit ohms bounces… 2nd dead on arrival as well..
Fascinating isn’t it? They are also wired backwards from what I’ve found. If you can be patient, you can find originals on FB marketplace, and it’s worth the wait.
Hey so what if the ohms readings are too high when tested from say S and to ground? Does that mean the fuel gauge is bad? I'm trying to get mine to work and get solid test light on I, flashing on A and dimmer flashing on S when the wire is disconnected, with the S wire connected the light flashes very very dim and the fuel gauge only moves to about 1/8 tank. Sending unit Ohms are 15 which should be accurate since the tank should be almost full.
Sorry so long in response. How high? More than an Ohm or 2 and the gauge is bad. Probably a deterioration of the coating on the resistor wires or a potential shorted connection.
Well I have the main power to the gas gauge and then the two posts that go to the coolant gauge both blank but when I try to put the test light on the sending unit wire nothing happens.
Also, my engine block temperature sensor does not flash any light when I put the light meter on it.
What does work though is if I turn the key on and I put a ground wire to the engine temperature sensor wire it makes the coolant temperature gauge needle go to hot.
This is definitely a ground issue. Email me at dellis6914@gmail.com and I’ll send you a wire diagram.
When testing continuity from the posts on the back of the fuel gauge to the speedometer housing, I have continuity from S, A and, I. Is that bad?
I have a spare speedometer and that one has continuity from the S post only.
Sorry for the delay. Let me check tonight and get back to you.
I did the quick voltage check on my temp gauge to see if the gauge would move. It moved the opposite way … more toward cold??? Any ideas?
I had the wires just like you showed.
Thanks,
Rock…. 78 CJ5
Nevermind…. The Omix cluster has the S and A posts of the temp gauge on opposite sides of the gauge. I should have known that by looking at which post the connecting strap in on.
I was just going to ask if they were aftermarket or not. Sorry I didn’t respond earlier.
i believe you may have a test wrong when measuring the +5 DCV . i would think you want to go to ground and and jumper going from the fuel gauge to the temp gauge.
Putting the leads of the volt meter across the jumper wont read the voltage because one of the leads needs to go to ground.
Hey bud how are I have a 1983 cj7 i replaced the fuel & temp gage they work out side the dash but I install cluster in dash they don’t work
Are your gauges original or after market?
So I have a question. I just recently installed a brand new sending unit and gauge worked fine for about a month then became stuck on half a tank. I dropped the tank and checked the sending unit and it was good. Then followed your directions to check the gauge itself. Everything seemed to be working fine yet my gauge is still stuck on half. What could be my issue?
Is the gauge aftermarket or original? Also, have you checked all the grounds? Sounds like a resistance problem.
My gauges work intermittently. If I put the test light on the sender post of the temp or fuel gauge, the gauge read, but I am guessing they are just reading the resistance of the test light circuit? I know my fuel sender is not grounded (waiting to burn through this tank of gas to drop the tank), but I can't figure out the temp sender...
The temp gauge is powered by the fuel gauge by way of the jumper strap that converts the voltage from 12 to 5. If you gauge has no power or ground the temp will more than likely not operate correctly. It’s amazing with these AMC CJ what a good ground will do for the whole system.
Okay, so S isn't flashing with a test light on the fuel gauge. When I removed the wire from the sending unit "S" it starts flashing. Does that mean I have an issue somewhere from the sending unit to the cluster?
That would be my guess. Another option might be the ground wire that runs from the sending unit to the frame. Did you do the test starting at the 19:00 mark?
When testing the temp gauge should you not be hooking up the positive to the positive on the fuel gauge to see if it goes through the by metal
That you can do. As long as you have everything grounded so you don’t blow up you gauges when running a current through them.
@@coolguy_CJ7 if they're not grounded how could there be current running through them?
I need to replace the fuel gauge. Do I have to take out the entire speedo cluster to do this? If so do you have a video showing how to remove it? Thanks!
First, are you sure it’s the fuel gauge? Second, yes, you’ll have to remove the speedometer. Third, no video on the disassembly of the speedo yet (soon).
@@coolguy_CJ7 Am I sure, hahahaha. NEVER!!! But I did drop the tank and check the sending unit and it is good to go. The Temp gauge is working so I assume there's power getting to it. Is there anything else I should check first? Thanks for all your help!
@@davebrown5403 Just the grounds. Did you try to “hot wire” the gauge to test it?
I haven't tried to hot wire it yet. Where is it grounded? @@coolguy_CJ7
I tried the alligator clips on the back of the fuel gauge while it was still in the dash. Got nothing. It still should have worked even though it was still hooked up right?
Correct. Did the gauge operate before the test?
No the fuel gauge was not working. But the temp gauge works. So there’s power getting over to that.
I am not getting a continuity sound when I go to make sure my fuel gauge is grounded to the housing.. what are my next steps? Why wouldn't it be grounded?
You should only have continuity between the A post and the housing. The S and the I don’t. There is a small metal strip on the back of the fuel gauge that connects to the housing. Are you sure that is clean and getting good contact?
My question is. How do you keep the gauge at full? I drive around town and it goes to E.
Don't think I can help you with that one. Might have to just accept that your MPG in town is somewhere are 8-10 :)
@@coolguy_CJ7 Ha. Bad joke, but I couldn't resist. :) Great videos. I use them a ton!!! Thank you for posting your work.
Or stay really close to a gas station :)
hi! any way to add rpm gauge to base 1980 cj5?
Yes. Possible. Easy? Probably not. Depends on if you want to go original or aftermarket. But either way, the Tach gauge will plug directly into your fuse box and then you will need the the wire in your engine bay that runs to the coil (green wire) or your distributor if you have an HEI.
@@coolguy_CJ7 OEM tach (for I6 and V8) SHOULD already have wires under the steering column. They plug into each other, so you just unplug them and tie them into the tach. Lighting circuit can tie into the clock power on the fuse box. Biggest PITA is cutting a hole in the dash (2-7/8") without making a giant cluster...
and your suggestion for a replacement sending unit is....?
Updated in the description. www.mtscompany.com/
Do you have anything on getting the oil pressure gauge to work?
Have you checked the oil pressure sensor on the side of the engine block? Have you checked to see if your getting signal voltage from the sensor? And have you checked to see if your getting anything at the gauge in regards to voltage?
@@coolguy_CJ7 The sender and the gauge are new. I haven't checked the voltage. Will do. It basically is pegged at 0 when I'm on the gas and bounces around 20 when at idle.
@@Christian-ux1vl is the gauge aftermarket?
@@coolguy_CJ7 Yes, it's a Crown product. The sending unit was new as well. I tested everything though I am uncertain about the ohms on the sending unit itself. I also grounded the sending wire to the gauge and the gauge pegged at max PSI so I believe that indicates that the wire and the gauge are OK. I suspect that method is not orthodox. I purchased a new sending unit and am waiting for that. I'll switch it out again and see if it works. There are a mixed bag of Jeep forum threads out there on this topic. Seems like a common problem. I still have the original gauge.
OK, new sender is in and the gauge is working now. 35-40 PSI on start up. When warm and at idle its around 20 psi and while driving it reads an increase in pressure when I'm accelerating put to about 45psi. I don't now how accurate the readings are, but this together with the new oil pump I installed, gives me plenty of confidence that the oil is moving about the engine as it should be. I am declaring victory.
I had a quarter of a tank reading mine is empty why is that
My initial guess it that your sending unit is not sending the correct signal (ohm amount) to the fuel gauge. Is your gauge original or aftermarket?
👍👍🇺🇲
I’ve come to the conclusion that it’s either the pink wire or the gauge itself. I’ve dropped the tank and replaced the sending unit and cleaned the ground connection.
Test the connectivity of the wire ends and the resistance. Also, test the ohms of the sending unit.
What gauge wire size are they for wiring the sending unit and gauge?
Because of this this video, I had to subscribe
So the peer pressure worked… :)
@@coolguy_CJ7 lol
I got my 1980 CJ5 back from a friend's shop. I had put in a new fuel sending unit. The tank is a poly 15 gallons. I never had a full tank, just maybe 5 gallons in it. Sometimes my fuel gauge needle will bounce a little, but not much. 2 days ago after I added about another 4 gallons of fuel by hand, when I start the jeep the gauge goes from before the E to on the E . When I turn key off, the gauge needle goes to before E. I am pretty sure the fuel gauge is working, otherwise it would not move. What should I need to look for, check the ground wire on the sending unit, drop the tank and check the float arm on the sending unit? Maybe see if it needs to be slightly bent? I did calibrate with my multimeter, and moved the
arm and it read 72 empty and 10 full.
When you said about the speedo cluster being grounded, is that with it in the dash, or does the speedo need a separate ground wire? Hopefully it is something simple. If you have anything to add let me know. Thanks so much. Your videos are very informative to all us jeep novices. I was wondering how to send you a video of my gauge before and after I start the jeep if you need to see it. Thanks
Mark Feuerherdt
Also. I have a light tester. So I will use that info on your video to test my gauges and fuel sending unit. Thanks!!😊
@coolguy..bro I'm nervous.. so it's ok to send 12v to the "I" post on the fuel gauge? I have a painless wiring kit I'm working on.🕵🏻♂️🤷♂️🥸
Just don't want to burn up the new gauge
As long as it’s ignition based and the speedometer is grounded by way of the tank sending unit, you should be good. Did I send you the wire diagram?