Fuel Gauge and Oil Pressure Gauge problems

[landonh]

I have a 1998 GMC Sierra XC K1500 5.7l

The fuel gauge will !!! boing !!! past full when key on and then immediately fall back to what seems to be a normal indication. But does bounce slightly.!!

The Oil pressure gauge bounces slightly. !!


The fuel pump was replaced a year ago.
The Oil pressure was bouncing before the fuel pump was replaced.

Help me please.

Thanks
Landonh

[stumpuller454]

i`ve seen one truck do that, it had a zillion k`s on it, kinda figured it needed a cluster, but customer didn`t care to fix it anyways, maybe see how much a cluster is from a wrecker, plug it in a see if that fixes it, unless they want an arm and a leg of course!!

[03chevy]

well the fuel gauge moves because the float is moving. when you gas on it moves to emty and brake moves to full right? thats the float could have a small hole in it. and the oil moves that is just the pressure. my truck does that. when it stays at 0 then you have a problem. but you have nothing to worry about unless you just like to have them setting still

[landonh]

When just sitting on the carport. Turn the key to on and the fuel gauge will blast past full then come back down. after that ir seems to stay the same some what steady but it aslo has a small pulsating action.


The oil gauge pulses[ about 5 psi ] when running again sitting still as well.

[03chevy]

that's normal. all my gauges do that except the tach. and speedo. "well my gas guage to but that needs to be replaced" but dont worry everything is fine. when they stop working then you need a rebuild like i have to have.

[landonh]

This is not normal for it just stated doing this.
before the fuel gauge would remain steady even when turning on the key or starting the engine.
I can see some small deviations being normal but to rapidly go past full when turing on the truck is not normal.

Thanks
Landon

[chengny]

My bet (because it is two gauges acting up) - the PC board. I just recently had some serious instrument cluster trouble and spent an entire night and most of the next morning with a Fluke meter and then a soldering iron fixing it.
It turned out that I had torn the PC board doing a lamp change. My truck is quite a bit older (86) but the basics should still apply.

Each gauge is fed by it's own circuit on the positive side via the pins on the harness connection but groups of gauges and the backlighting (those little 168 bulbs that I was attempting to change) are grouped together on the negative side. And to make things even more difficult - they are not always adjacent to each other. The back side of my instrument cluster has so many Sharpie marks on it now, it looks like a mad professor's chalk board.

But now I do know that the negative legs link more than one device and do not necessarily have to be near each other.

BTW - when they say PC board do not picture a computer mother board for example. Think more along the lines of two sheets of thin clear plastic with gold leaf sandwiched between them. At the appropriate spots the back piece of plastic is open to reveal the copper etching.

All this advice is predicated on my assumption that your 1998 instrument cluster is constructed in a similar manner to my 1986.

[crabtruck]

I'm kinda in chengny's camp with this. Sounds to me you have a capacitive leak.
A little techy I know, but what it means to you is that you should inspect the traces on the IP board.
BTW traces are what you call the flat stuff used instead of wires.
While your gauge could have given up the ghost, I don't think so.

Closely look, using a magnifying glass if needed, at the trace that runs
from the gauge to the sending unit connection point.
Look for anything that might act like a bridge to elsewhere,
probably something "hot" not a ground.

Also check the trace for the gauge ground, definately with a magnifying glass,
looking for breaks, nicks, "thinness" or any other damage.

If you find a bridge, cut it with an Exacto knife or something equal for small and sharp.
If you find a bad spot, repair it with a clean solder bridge. Do not over heat board, be delicate.

What traces go where may be confusing at first. One way of sorting them out is
taking a picture of the board and printing it out. Then you can make notes on it until sensible.

[landonh]

I have included an image to help show my problem. I replaced the Fuel pump relay but still no good situation.
Thanks
Landon

[chengny]

You know what, you have probably already done this but if not, check and be sure that your engine and cab grounding connections are clean and tight. This is a classic sign of an intermmitent gounding failure.

If that doesn't help, have a helper sit in the cab. Then, while he watches the affected instrumentation, you go around and start randomly wiggling groups of wires (esp. at the firewall area and underneath the dash). Not the most scientific diagnostic method, but it will oftentimes point you in the right direction

BTW - Disregard my previous advice about the PC board - I was drunk.

Just kidding, the dash cluster you have is much newer than what I was describing and most likely has nothing to do with your problem.

Pray tell, how did you manage to attach those images to the thread? I am currently working on a factory AC installation and the problems I am having would best be described with visual images. I see no option to attach images on this page.

Help please?