Erratic Gas Gauge

[not2melo]

Well the gas gauge has started to screw up and not read the proper levels.
When I first start the car up it reads 1/2 a tank and then over a period of time it rises higher.
Then the DIC is reading wrong also and give speratic readings from time to time.

I only us Sunoco 94 in the car but do not know what the previous owner used.
Time to get the gas sender unit replaced I think?

 

[Riley P]

Tough one to say as I have no idea, but I can share my experience. Coming back from Vegas, I never had a problem with the car...until the last corner to my house when the needle dropped to E. Confused, I went and filled it up, it was the gage. Going through two cans of Sea Foam and only using Esso fuel and my gage slowly started to return to normal after 5 of 6 tanks. While I was having the problem, it would read a certain amount at start up, then slowly rise to a higher reading as I drove. I never noticed this on the drive back, but then I always kept the tank over half full.
How long have you had your car and if it hasn't been very long, I would try some Sea Foam first, wait a few tanks, then replace the fuel sending unit if there is no improvement.

 

[OBSESHON Mark]

Hey Greg this is quite common on the C5's

There is a fuel additive called Techron that usually solves this problem.
Most guys buy it in the U.S. I am not sure if it is available here.
Good luck.

 

[Riley P]

Hey Greg this is quite common on the C5's

There is a fuel additive called Techron that usually solves this problem.
Most guys buy it in the U.S. I am not sure if it is available here.
Good luck.

:agree: I heard of Techron as well, but could not find it here, so that is why I hit the Sea Foam. I hope your car gets better soon.

 

[not2melo]

Originally Posted by OBSESHON Mark

Hey Greg this is quite common on the C5's
There is a fuel additive called Techron that usually solves this problem.
Most guys buy it in the U.S. I am not sure if it is available here.
Good luck.

I have actually used that before picked up 2 cases last year off a member on the another forum.
I put one in last year in the summer as the gauge stuck once and one in this spring so far same problem.

Originally Posted by Riley P

I heard of Techron as well, but could not find it here, so that is why I hit the Sea Foam. I hope your car gets better soon.

What is this Sea Foam and where do you get it?
I think the fuel sender maybe shot but who knows worth a try.
Thanks for the input guys.

 

[BAD-C5]

Well the gas gauge has started to screw up and not read the proper levels.
When I first start the car up it reads 1/2 a tank and then over a period of time it rises higher.
Then the DIC is reading wrong also and give speratic readings from time to time.

I only us Sunoco 94 in the car but do not know what the previous owner used.
Time to get the gas sender unit replaced I think?

Your key is the data, being the voltage sent to the PCM for fuel gauge function.
Now, obviously, your losing the actual transfer voltage somewhere along the line.
That means one of two things is occuring.
First, your jet pump is not working or your fuel level sending unit isnt working.
So, at a half tank, you need to see what is going on.
A quick way to determine that, is to check your voltage on the signal wire for that sending unit or if your not good with a DVOM, remove the pipes off the passenger side unit.
If you are full, that tells us that for some reason, your jet pump isnt working.
If you are empty, or close to it, that tells us that the voltage isnt correct.
If you are competant with a meter, let us know what you find out

 

[not2melo]

Thanks for the info, I am looking into the Sea Foam, if that does not work then will look into it further.
Just filled up and the gauge is working again so far just does not go all the way to the far right on full fillup.
I will try the Sea Foam and see what happens in the next few weeks.

 

[powderextreme]

This is a common problem with the C-5 . The sending unit inside the tank gets a build up of varnish from the additives in fuel . Only run premium fuel as well in the car. Regular has to many sulfur type of additives. I myself have had no problems since I have been using Esso fuel only.

 

[not2melo]

I have run Sunoco 94 since buying the car, dont know what the previous owner used.
Is it an actual varnish buildup on the sensor or is it the sulfates eating away at the resistive coating?

 

[Riley P]

Sea Foam is basically...hard to explain. Apparently it does a lot of different things. It is a petroleum product that acts as a....um, you better read it for yourself.

Sea Foam

I think my problem was varnish build up on part of the sending unit because if it had been sulfates eating the resistive coating, the gage would never have returned to normal.

Just remember if you try Sea Foam, that it did not work right away but my gage slowly returned to normal a few tanks of fuel later, so although I used it and in the end my gage works, I can not 100% say it was due solely to the Sea Foam...but I bet it still helped.
I bought my Sea Foam at NAPA.

 

[not2melo]

Thanks for the info bud, I will check with my local NAPA or Part Source today.

 

[snopro925]

buy the gm fuel system treatment, ford and chrys dealers even use it, it removes the oxidizing from the brass contact on the level sensor contact. Usually fill tank following adding, run 2 tanks through it and its back to normal
sometimes is only a short term repair 1-2 years

 

[reco99]

Techron can be purchased at any Chevron gas station. I tried to get it at a parts store but they had no idea. Anyway I used a bottle in my car and always use the highest grade fuel too. My gauge goes to zero when it goes just below 1/4 tank. But sometimes shutting it off and restarting it will correct it, not always though. So far the Techron has not seemed to help.