Due to the long cold winter (maybe) my gas gauge is no longer working properly. It started a couple of weeks ago, I had about a quarter tank of gas and the gas gauge started moving back and forth wildly, it went all the way to empty and the low fuel buzzer came on, then seconds later it moved all the way up to full. It did this a couple of times, then sat at full. Now when I start the car up it seems to go to the direct level, but after I start driving for a couple of minutes it goes back up to full. The odd thing is if I watch the range on the overhead console it moves to accurately match the gauge, range of 240 when I start the car then jumps up to over 300. when the gauge moves to full. Anyone have any ideas on this one? I'm guessing it can't be the stepper motor in the gauge as it does move, perhaps a bad sending unit? Or I heard there is a plug going to the sending unit that may be shorting out? Hopefully once it warms up here I will be able to find the door in the trunk and unplug that connection and clean the terminals if that might be the problem. If anyone has had this happen and knows how to fix it please let me know.
Thanks
Dave C

 

I have heard of the stepper motors causing issues similar to this. Could also be a dirty connection or a ground getting rusted somewhere.

I personally had this issue with my fuel gauge but I also had a issue with my map sensor and tps sensor as well all at the same time. I ran test after test and narrowed my problem down to the pcm sending out wrong current for the 0-5v references. I swapped my pcm and the "ghost" issues were gone!

 

And BTW the fuel access door is right behind the rear seat under the carpet centered in the trunk. Easy to get 2!

 

Thanks Turbo! I just took a video of what happens, I cycled the key on and off a couple of times, when the car is running it goes to full, but when I turn the key to the first detent the fuel gauge seems to be working correctly! But as soon as I turn it to run it goes back up to full...

 

Just found this on Youtube, and got new stepper motors off of ebay. Looks like I will have to take off all of the needles before i can get to the steppers, so might as well replace all 6 motors since if I only do the bad one the rest are sure to follow as soon as it's all back together (if that is even the problem)
Dave

 

OK just changed out all of the stepper motors and NO FIX! Still having the same issue with gas gauge, it seems to be in the correct position when I start the car, but after driving for a couple of minutes it goes back to full. No idea what to try next, I pulled away the carpet in the trunk and opened the access panel to the fuel pump, all wires looked good, I unplugged them both and sprayed some contact cleaner in them, closed everything up and same thing still. Anyone know where the ground is located for the rear wiring harness? that might be my next try. Or is there a way to test the sending unit in the tank? Running out of ideas...
Dave

 

Dave:
I would check all the body grounds before changing out the PCM... as John suggested.. It may also be a bad sending unit in the fuel pump... I don't know how often you've run it on empty..but it may be the problem as well.

PCM's aren't cheap..
Me personally.. I may go with a new fuel pump...
How many miles on it? I had to change mine out at 80,000... Because it was failing and my fuel pressure was low...

Just a suggestion...

 

Thanks that may be the next step, I am getting some resistors, I saw something online if you put a 100 ohm resistor between the ground and purple signal wire from the sending unit it should show around 1/4 tank with the key on. An easy test to see if the gauge is working properly I guess. I bought the car with 110,000 miles on it so do not know if the previous owners ran it out of gas, but the gas gauge was working properly for the first 3 months I owned it. I just got a new floor jack this past weekend so will be able to jack it and look underneath for ground wires, clean them up and change the fuel filter while I'm at it.
Will report back with any information that I find out.

Dave

 

Well I solved the problem. first I tested the gas gauge by unplugging the fuel pump sending wire and using a 125 ohm resistor between the ground black wire and sending purple wire. This caused the gauge to go to about half a tank. Then I tried the same thing with a 150 ohm resistor and the gauge moved to 3/4 tank as it should. So I ordered a new AC Delco fuel pump/sending unit which I was able to find on ebay for less than $200 with free shipping. After removing the old fuel pump/sending unit, I repainted the locking ring since mine was all rusty. After the paint dried overnight I baked it in the oven for 30 minutes at 300 degrees and it was nice and hard. I put the new sending unit in the tank and had some trouble getting the locking ring back on, it takes more than 2 hands! I pressed down on two sides of the ring while my friend used a drift and rubber mallet to turn the ring until it locked in place with the plastic lock. I reconnected the 3 fuel lines and the 2 electrical connectors, hooked the battery back up and turned it over a couple of times to prime the pump, then it started right up! And the gauge went to the correct level of 1/4 tank, which was pretty close based on the mileage driven. So mission accomplished!

 

Was that hard to do and how long did it take? A mechanic told me it would be between $500 & $700 to do this for me, then I've heard it's easy to do and the parts only cost about $100 for the sending unit. True or false?