99 C5 Fuel Problem
Thread Starter
Intermediate
Joined: Jun 2008
Posts: 28
Likes: 0
From: Columbia Missouri
99 C5 Fuel Problem
I filled up the tank this afternoon. While sitting in traffic the fuel gage drops from full to emtpy (about .1 sec elapsed), check gages light comes on and low fuel displays on D.I.C. I checked underneath for leaks saw none. Went to the nearest gas station tank is still full. Tried turning off the car and restarting, still comes up. Read the codes; zero present (no check eng light), fuel monitor status checks ok (according to the code reader). I called a friend at a local dealership, he said it might be the fuel sending units and that i would have to change them in both tanks. 
Any other ideas, or info on why both need changed? Thanks in advance.
Jamison
Any other ideas, or info on why both need changed? Thanks in advance.
Jamison
Pro
Joined: Jul 2008
Posts: 564
Likes: 1
From: Moyock NC
Mine does this from 3/4 to 1/2 tank its a common problem with our cars you can put some Techron fuel treatment that will help.
I also statred putting Shell gas in it only and it has only done it once with that gas in it I sure someone can add alot more about this but this what has happened to mine.
I also statred putting Shell gas in it only and it has only done it once with that gas in it I sure someone can add alot more about this but this what has happened to mine.
Safety Car
Joined: Apr 2003
Posts: 3,732
Likes: 21
From: Napa Ca
Very common C5 and other GM vehicles problem. You'll find tons of threads on this problem. Cause of the problem is the high sulfur content of some gasolines which cause deposits on the fuel sender sensors. Top Tier gas usually better than off-branded gas. If you have Chevron in your area try that along with a bottle of Chevron Techron Concentrate Plus Fuel System Cleaner (there's a similar looking bottle labled Pro-Guard Fuel Injector Cleaner also from Chevron - get the concentrate) available in most auto parts stores. Try several tanks of Chevron or something similar such as Shell along with an appropriate amount of Techron. Try not to let the gas level get too low or park the car for more than a few days with a low tank. Other products out there can help too...someone else is bound to reply to this thread and a search will turn up more answers than you will care to read.
Advanced
Joined: Feb 2001
Posts: 74
Likes: 0
From: Mississauga Ontario
I bought the Chevron Techron at Pep Boys on Saturday, $15.00 per bottle. Best results if poured into a near empty tank and let it sit / soak. Instructions are on the bottle and in many other threads.
Instructor
Joined: Jul 2005
Posts: 236
Likes: 0
From: CT
If Techron doesn't work try
Very common. My 97 was going through this and I tried the Techron but it didn't help my car. Then someone suggested Seafoam. Weird name but it is at Autozone, etc. This one did the trick for me after two cans. But more then likely it was probably all the Techron and then the Seafoam together. Whatever did the trick, I haven't had a problem in over two years. Yea.
I filled up the tank this afternoon. While sitting in traffic the fuel gage drops from full to emtpy (about .1 sec elapsed), check gages light comes on and low fuel displays on D.I.C. I checked underneath for leaks saw none. Went to the nearest gas station tank is still full. Tried turning off the car and restarting, still comes up. Read the codes; zero present (no check eng light), fuel monitor status checks ok (according to the code reader). I called a friend at a local dealership, he said it might be the fuel sending units and that i would have to change them in both tanks.
Any other ideas, or info on why both need changed? Thanks in advance.
Jamison
Any other ideas, or info on why both need changed? Thanks in advance.
Jamison
