The infamous GM fuel pumps ('98 and up)

[atomicpunk]

From searching around in this forum, I can see that many of you have experienced the common problems associated with the fuel "modules" used in GM light duty trucks from 1998 and up. However, I'm experiencing an additional problem that I'm hoping someone can help me with:

Vehicle: 1998 Chevy Silverado K1500, 350cid

I bought this truck used from my boss last November with 139K on it. The fuel gauge had stopped working several thousand miles prior to me buying it, and was always on "empty". Since the day my boss picked the truck up, the pump was loud as hell, and I knew when I bought the truck that I was on borrowed time with that original pump.

Almost two weeks ago, with the odometer now at 149K, the check engine light came on. Luckily, my Dad is a mechanic at an independant garage with A) 30+ years experience and B) a Snap-On Scan Tool. One of the codes was the EVAP, or "gas cap" code, and the other related to the voltage going to the fuel gauge (if I remember correctly). Hoping it was a random glitch, I cleared the codes. Once I started the truck after clearing the codes, the fuel gauge immediately shot to the "full" position, and was vibrating extremely fast while humming slightly. It stayed like this for a couple days, then fell back down to the "empty" position. Almost a week later, the check engine light came on again. I found that the same two codes triggered the light, and the same thing happened after I cleared the codes.

Figuring that was strike two, I didn't want to take any chances and end up getting stuck on the side of the road. We ordered a Delco pump from the GM dealer, which listed for $527, however I was able to get it through my Dad for $370 (thanks Pop!).

We changed the pump and fuel filter the following day. Removing the bed is probably the easiest way to change the pump in your driveway, but since I had access to a lift, we dropped the tank. Since I hadn't planned on changing the pump until the day prior, I still had half a tank of gas (13 gallons). The good thing was since the pump was still functioning, we disconnected the line at the fuel filter, and then jumpered the fuel pump at the relay to use the pump itself to empty the tank. My Dad said that he has probably changed 100 of these pumps over the last few years, and most all of them have had dead fuel gauges as well. (By comparison, he can't remember the last time he changed the fuel pump in a GM car...) The sending unit for the fuel gauge is part of the "fuel module", and can be replaced on it's own. I wouldn't recommend doing this though, since the fuel pump has to come out to access the gauge sending unit, you might as well bite the bullet and change the whole thing. Just like changing a water pump with a timing belt...

OK, Here's where it gets weird...after successfully installing the new pump, the fuel gauge now works- kinda. As you are turning the key to start the engine, the fuel gauge (none of the other gauges) voilently shoots to the "full" position and bounces around, then quickly settles "near" where it should be. I say "near" because it seems to be off by about a quarter of a tank- after filling the tank, the gauge only goes as high as about 3/4 full. In addition, under all driving conditions, the gauge needle is still vibrating extremely fast, so fast that you wouln't neccessarily notice it until you compared it with the other gauges.

My Dad has never seen this happen before. I've tried pulling the entire instrument cluster out, just to see if it might "reset" the gauges, but it didn't help. The only other thing I can think of is a bad ground, but I would expect different symptoms from the gauge if that was the case.

The trip odometer has been my best friend as I've learned to live with a disfunctional fuel gauge since I bought the truck, but I really hoped that the $370 module would solve all my problems.

Has anyone else experienced this problem?

(sorry if I was rambling...I'm kinda detail oriented!)

[brumleveb]

My boat's gauge does the same thing. For a second or two after turning the key to on, the fuel pump primes itself and the the needle in the gauge vibrates signifcantly. After that, the pump quits priming and the gauge settles down.

[rcb98chvy]

mine is doing the same thing with 317,523 miles guage shakes violently and goes from full to empty in a blink lol the pump is still going but is loud always has!?! my guage does react to movement at the break pedal and the column shift! crazy... love the trip meter though!

[atomicpunk]

HOLY CRAP! 317K, on the original pump?!!

What engine do you have in it, just out of curiosity?