Fuel gauge not registering properly

HANK SIPSMA

MEMBER
1984 JEEP CJ7
4.2L
6 CYL
4WD
MANUAL
100,000 MILES

The fuel gauge (which is brand new) will not read full when the sending unit is at 10 ohms (which should be full). The range of the sending unit is from 10 ohms full to 76.5 empty. I have shorted the sending unit lead to ground and the gauge goes to full, however, when connected to the sending unit (I have it out of the tank) it does not read properly, and max about 3/4 of a tank. I have checked that I have good grounds, which I do, and also checked for 12 volts at the I terminal of the fuel gauge (which I have). The only anomaly is that on the A terminal. Or jumper terminal to the temperature gauge I have 12 volts also. Shorting the temperature sender input to ground the temperature gauge goes approximately half way. To be frank, I don't know what else to check. Thank you

1 Reply

CJ MEDEVAC

MECHANIC
11,004 POSTS

Sounds more on the sensor part.

Do not! Play with! Power up the cluster unless it is installed on the dash, or you have it grounded multiple times so it is impossible to come "Ungrounded".

I hope it's not too late! (Is it fried or damaged?)

In order for the sender to work (in or out) It will need a good ground too.

Insure your sender wire (pink) has a good connection to the sender.

Now really look this part over before you proceed.

The float swings in/on a pivot hole. On either side of the swinging arm is a a "bendable" (limiter) tab. Look good!

With some needle nose pliers, bend (either the full side tab or the empty side tab) carefully and slightly to allow a little more movement (and be able to put it back, if need be!).

This will increase or decrease what the gauge reads (and may increase or decease the floats travel).

I have a 21 gallon polyethylene tank, I wrote this elsewhere, this info might also be something to store in your head too!

Pasting

A fuel gauge sender is never accurate right out of the box and one end or the other will never be spot on!

I draw my specs on a door facing (kind of my out of tank jig!) And bend the rod, move the limiters until my float is perfectly on top of the "Bottom of the tank mark".

With lots of gentle tweaking (jumper wiring to the gauge at times) I get the gauge to show "almost" dead empty.

To me, the most important reading!

On mine, I have the full end actually showing "way over" (hiding) at the top of the gauge. As long as it's up there I have plenty of fuel.

I do all of this and check my readings before I install the sender.

I could figure the exacts per increment, but I haven't. I'm pretty used to how it works now.

Notice the 5 gallon can back there, I'm at peace knowing if I run out, I have more.

The biggest plus I got out of it is a long time back, Work was a good ways off I had to fill up every 2nd day, this tank got me 3 days (and some).

It's a 21 gallon tank, Slap full coming out of the fill hole, it will hold exactly 22 gallons.

I suggest the polyethylene tank, ethanol will rust things up fast, insure you get the correct tank the fills and other items vary from Jeep to Jeep, usually the right year will get the right tank.

Un-pasting

Let me know what you come up with, I'd like to see your results before I add more confusion!

Lacking good pics of my '77 CJ-5s sender---I have included a few from my '46 Willy's sender and gauge.

Images (Click to make bigger)