79 CJ7 fuel sending unit

[JeepBunny]

My sending unit was replaced but my fuel gage is still not working properly.

Originally we thought the cluster gage in the dash was bad. After changing the cluster twice, the sending unit was replaced. It worked fine for a while, but then the gage started acting up again. It would read 3/4 after I filled it, then a half, now it's down to reading at a quarter tank after it's been completely filled at the pump.

My question is, is the sending unit bad, or is there an adjustment that can be made?

 

[Torxhead]

It is possible to check the sending unit by checking the resistance between the ground and the sending unit wire prior to and after a gas fill up. There is a write up on the net that should help you with your issues with CJ gauges, look up John Strenks CJ gauge page.

 

[JeepBunny]

Thanks, I'll do that

 

[Airstrike]

Here are the 2 links that I saved. They really helped me alot. In the end.. alwyas make sure you have a really good ground.

The new Gauge Page

Basic Troubleshooting for CJ gauges

 

[JeepBunny]

Coming back to update this 3 years later.

...it was a bad ground.

 

[Torxhead]

Bad grounds are quite common on an old rusty CJ, there have been quite a few writeups on them. The way I see it the most critical is the black ground wire coming from the ignition control module which is located behind the coolant return bottle. It runs to the distributor and was installed there for dealer test purpose, from what I have heard. I just snipped mine and ran it directly to the battery negative. The distributor does not need it. The battery charging system can be helped by running a wire from the alternator housing to the battery negative also. The biggest electrical draw on the CJ comes from the starter which can be helped from an additional wire from the starter housing or a point nearby to the same battery negative location. The list goes on and on, Cast iron and sheet metal are poor conductors of electricity, made worse by rust, paint and grease, AMC made it that way to save money. Thanks for the update.