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!)

[Rbraczyk]

I had to get it changed on my 94 deville. It just quit. 600 dollars later...

[Faze2183]

well my moms is doin the same thing but the fuel cap thing is the same thign we have and etc....and but ya her fuel gauge is funky too

[gmsmallblockguy]

Could be that someone had tride to fix it in the past and pinched a wire sending 12VDC into the fuel level sending unit and caused damage to the magnet and/or circutry that drives the needle.
Have you tride checking the harness for damage, a previously botched repair attempt, or evidence of a previously incorrect connection?

I'd probably start with checking voltages in the harness going to the tank. Or swapping the guage pannel with a known good one.

[atomicpunk]

Luckily, I know the entire history of the truck, and from that I know that nobody has done anything to the fuel pump or tank until I changed the pump.

Checking the voltage at the harness is a good suggestion, the cluster swap would be even better- if I can find a willing participant with another '98.

Do you know if there is a ground wire in the harness going to the pump? I haven't had a chance to mess with the ground strap that runs from the filler neck to the frame yet, but I don't know if that will even make a difference.

I'll have to see if I can get my hands on a good schematic...

[Karen512]

What did it take to fix your gas guage??? Mine is out on my 98 2500. It just flips back and forwards from E to F.

[atomicpunk]

I haven't fixed it yet- it's still off by about 1/4 tank, and it is still vibrating.

It sounds like your sending unit for your gauge is on it's way out. How many miles do you have on the truck?

[Karen512]

I have 180,000 miles on the truck. The gas gauge has been out for about 6 months.

[atomicpunk]

If you haven't replaced the fuel pump yet, I would probably do it before it quits on ya. When you buy the new pump, it will come complete with the fuel gauge sending unit- that should fix your gauge problem.

Be prepared...the Delco pump module is pretty pricey!

[Karen512]

Thanks for the advice. I just hate having to spend ass tons of money on dumb problems!!!!!!! Ya know. Oh well, I guess it needs to be fixed. (I ran out of gas last week on my way to work! Oops!)

[Karen512]

Check out my truck in my gallery if u want

[ecal533]

Had this problem with my 98 with the 4.3. I had intermitant fuel pump problems and the gauge always apeared to vibrate until it quit totaly. I choose the pull the bed off method. Very easy to do. I replaced the pump 3 times until I read where the harness goes bad often on these. I bought a GM harness for a buck 24 and the pump has run beautifully ever since. The bad news is that your gauge is just plain bad. I got a used Instrument cluster for $60 at a bone yard. When you put it in you are going to want to leave the dash apart, along with the clear lense. Fill your tank, and then pull the needle off the fuel gauge and position it right on full. This will give extra miles when you hit empty. Its all working great now.

[chebby uno ton]

Originally Posted by Karen512

What did it take to fix your gas guage??? Mine is out on my 98 2500. It just flips back and forwards from E to F.

My partner has a 99 2500 with the 6.0 in it. We had been driving all over the east coast to jobs and the gauge would flop around like that. Then we got some bad gas (mostly water) in N.C. and the fuel pump quit on the lonely stretches of interstate 81 in PA. After a very expensive new pump the gauge works fine. The new intank GM pumps SUCK!