Fuel gauge question

Fuel gauge question

grunt

Active Jeeper
Posts
284
Thanks
0
Location
Connecticut
Vehicle(s)
1979 CJ 304, 400 automatic
Having issues with my fuel gauge. Seems this is common. Anyway went to the "Basic Trouble shooting for gauges". I'm getting power to "I " terminal, getting the "flash at "A" terminal and getting the dimmer flash at "S" terminal. If I pull the pink wire off the "S" terminal and then using my test light and one end grounded and the other to the pink wire I should see my test light pulsating? Correct? Seems to me before I did this and I was getting the pulsating light, now I'm not but with the the pink wire connected to "S" terminal I am. By the way when I pull the pink wire off the sending unit at the fuel tank and use my test light I get the pulsating light. Any thoughts? I would appreciate it....
 
Last edited:
A test light is a cheep and easy way to troubleshoot most electrical problems but the resistance of a fuel sending unit varies depending on how full the tank is. A fuel gauge is simply a meter trying to read that resistance. Now's the time to buy a digital multi-meter.

Here's 2 good pages to help out.
http://www.4x4wire.com/jeep/tech/electrical/gauges/


http://home.roadrunner.com/~john.strenk/Gauge%20web%20page/basic_troubleshooting_for_cj_gau.htm

Thanks for the reply...I have been reading up on John Strenk's info on your 2nd link before I posted this thread. I have a multi-meter. I'm just curious when you pull the pink wire off the fuel gauge are you getting any voltage from it? Doesn't mention anywhere in in John Strenks trouble shooting guide that I see...
 
Last edited by a moderator:
Thanks for the reply...I have been reading up on John Strenk's info on your 2nd link before I posted this thread. I have a multi-meter. I'm just curious when you pull the pink wire off the fuel gauge are you getting any voltage from it? Doesn't mention anywhere in in John Strenks trouble shooting guide that I see...
If you remove the pink wire at the tank then you can test the sending unit. With the jeep off use an ohm meter (Multi-meter set to resistance). Read the resistance from the terminal where the pink wire WAS connected (not the wire but the sending unit). The resistance will tell you if the sending unit is good.
If the tank is full you should get 10 ohms
if the tank is empty you should get about 70 to 73 ohms.

BTW I had a problem with the first page I tried to link to. I think I have it fixed now.
Jeep CJ Gauge & Sender Diagnostics

EDIT: oh and what are the symptoms? Does the gauge always say the tank is full? empty? always too low?
 
EDIT: oh and what are the symptoms? Does the gauge always say the tank is full? empty? always too low?[/QUOTE]

Fuel gauge usually reads empty...checked all the grounds etc. Can't seem to figure it out......Once in a while if I bang the speedo , it will work for a while.......still curious... if I pull pink wire off fuel gauge and test with mm or a test light should I get power? Can someone pull off their pink wire off the fuel gauge and confirm this? Thanks.....
 
Great information! Been having trouble with mine for some time now. Shows full all the time until it is almost empty and then it goes to 1/2 tank.
 
Fuel gauge usually reads empty...checked all the grounds etc. Can't seem to figure it out......Once in a while if I bang the speedo , it will work for a while.......still curious... if I pull pink wire off fuel gauge and test with mm or a test light should I get power? Can someone pull off their pink wire off the fuel gauge and confirm this? Thanks.....

Shows full all the time until it is almost empty and then it goes to 1/2 tank.

Fuel gauge reading empty too long means there is too much resistance. That could be a bad connection.
If you can remove the wire off the sending unit the next step is to read the resistance. Fill your tank. The resistance of the sending unit to ground should be about 10 ohms. As your tank is getting low the resistance should rise. When you are out of gas the resistance of the sending unit should be 73 ohms. We are talking resistance here (measured in ohms) so a test light can't test your sending unit any better than a compression tester can test an ignition system.
Now if we test the sending unit as good then your problem is either the wire going back to the gauge or the gauge itself. It is uncommon for a wire to go bad but a bad connection at either end is possible.
What I think is most likely your problem is the fuel gauge. You say banging on your speedo sometimes makes the gauge work. If everything else checks out you may want to get an aftermarket fuel gauge. The OEM gauge in the speedo often gives us problems.

To double-check your fuel gauge before replacing it take the wire off the gauge that goes back to the tank sending unit. Short this terminal out to ground with a 10 ohm resistor. The gauge should say full. Use 2 ten ohm resistors in line and it should read slightly more than half full.
If the test of the sending unit is good, and the test of the gauge is good then the problem is the wire between the two. As I said before the connections on either end are more likely to cause your problem than the wire itself.


EDIT: this is Grunt's thread but Txquailhunter is also chiming in. Are you guys having the same symptoms or am I getting my facts mixed up?
 
Last edited:
Thank you. I'll follow your direction and let you know what I find.
 
Thanks BusaDave9,...tested the sending unit for ohms and it is good. Check the ground wire for ohms there and that is also good. Now my fuel gauge stopped working all together. Checked all the ohms readings at the fuel gauge and half the readings are bad now now. I guessed I trashed the gauge. Ill have to pick up a resistor soon and double check but its not looking good.... Another question. Everyone here says to find the gauge made in the good old USA. Where do you find these? Also can I find another original CJ jeep fuel gauge in "working order" and replace mine? I would think it would be ok. Thanks everyone for replying to this thread.....
 
Everyone here says to find the gauge made in the good old USA. Where do you find these? Also can I find another original CJ jeep fuel gauge in "working order" and replace mine? I would think it would be ok. Thanks everyone for replying to this thread.....

I recommend AutoMeter gauges. They are high quality. The down side is you will have to mount it under the dash. The OEM gauge will be non functional. That's how my CJ is. This is why I don't like the all in one speedometer.

If you get another fuel gauge for the speedometer that should get the job done but it won't be as accurate or reliable as an Autometer.
The decision is yours: accuracy or clean all in one look
 
I recommend AutoMeter gauges. They are high quality. The down side is you will have to mount it under the dash. The OEM gauge will be non functional. That's how my CJ is. This is why I don't like the all in one speedometer.

If you get another fuel gauge for the speedometer that should get the job done but it won't be as accurate or reliable as an Autometer.
The decision is yours: accuracy or clean all in one look

Ok great...If I do get the AutoMeter fuel gauge , which one is compatible to my original sender with the brass float? :confused:
 
This is the one I will be installing in my jeep. The range is 73-10 ohms will work with the stock sending unit.
 
Ok great...If I do get the AutoMeter fuel gauge , which one is compatible to my original sender with the brass float? :confused:

AutoMeter has lots of styles. To narrow down what look you are going for use their Gauge Selector:
Auto Meter - Gauges
Then check out their Advanced Gauge Search:
Auto Meter
The range is 73-10 ohms will work with the stock sending unit.
As ColdAir said you mainly want to make sure the range is 73 to 10 ohms. The gauges that will work with a CJ also say they work with ford.
Here are some options:
The Procomp 4315
4315_d.jpg




Part 1423
1423_d.jpg




The AutoGauge series is a lower cost series by AutoMeter
Here is part #2315
2315_d.jpg





Once you find a gauge you like google search Autometer and the part number. Click on "shopping" on the left. Even if you stick with AutoMeter there are lots of options for a CJ fuel gauge.
 

Jeep-CJ Donation Drive

Help support Jeep-CJ.com by making a donation.

Help support Jeep-CJ.com by making a donation.
Goal
$200.00
Earned
$85.00
This donation drive ends in
Back
Top Bottom