1992 Silverado surging

biggene · August 12, 2005

Ok new guy here with a major question.

Our 92 silverado was running great, then I did a tune-up on it. I changed plugs, wires, rotor, cap, pcv valve, and air filter. Then we took a trip to Florida, maybe 400 miles. Since returning, the truck does not want to run when it is first started up in the morning. It acts like it has no power at all, but if you let it warm up for 10 minutes or so, it runs great for about an hour or so, then starts surging and running like crap again.

I thought it might be the fuel filter so we changed it, and it was pretty cruddy and stopped up. After that the truck ran great for about 3 days, then started doing the same thing all over again.

Now I am about at my wits end, I dont have any other ideas of what it could be. I think it could be the fuel pump, but if it was wouldn't it run like crap all of the time?

Any ideas?

Thanks for your time and effort,

Gene

dgood · August 12, 2005

Had a similar problem in a 91 Corsica where the little gasket that sat between the PCV valve and the housing got lost and caused a vacuum leak with the same symptoms. Not sure if the trucks had the same gasket, but it's worth a look. After replacing, it ran like a top.

Wingnut · August 12, 2005

Did you clean the throttle body?

biggene · August 12, 2005

Oops sorry, lol.

Yes, I did clean the throttle body, used 2 full cans of B-12 spray. We also ran a can of b-12 through the gas tank thinking that the injection system might be clogged up and need to be cleaned out.

Gene

71GMC_3/4T · August 12, 2005

Change the fuel filter again. Maybe you got a tank of crud from one of the gasoline suppliers. If it ran great for 3 days and took a dump again, I think I'd be trying another filter before I spent too much time on anything else.

On my 71GMC, it sat for who knows how many years. After I got it running, I was changing a fuel filter every week for several weeks until I got all the junk out of it. I also had the tank steam cleaned inside, which helped a lot, although yours shouldn't be that bad yet.

biggene · August 12, 2005

Ok, I am on the 3rd filter in about 6 weeks now and it just seems to be getting progressively worse. Im wondering if it could be the sock on the pump itself stopped up?, or maybe the pump is on its final legs before giving out. I need to have the fuel pressure tested, just not sure how to do this myself or if it is possible.

71GMC_3/4T · August 12, 2005

It does sound like the sock or the pump could very well be the problem. A brand new filter offers very little back pressure so it can flow much easier. Once it gets a little crap in it, the pump has to work against more back pressure and isn't happy any more.

I had a '92 Z-71 and it had 160K miles when I sold her early this year. Still on the original fuel pump and running strong though. I heard it's a lot easier to change the fuel pump by lifting the bed up on one side rather than trying to drop the tank. Glad I never got to experience that though...

biggene · August 12, 2005

Ok I guess this weekend I will try swapping out the fuel pump and sock. I will go ahead and install a new filter inline while I am at it, and I will post again next week if I am still having issues with the truck.

Gene

biggene · August 14, 2005

OK, Here is an update. I changed the fuel filter, and it ran somewhat better, but was still spitting and sputtering when you gave it gas. I went back to my manual and it said timing, so I checked the timing, it is dead on. Next it said to check the igniton system, so I checked the igniton module, coil, cap and rotor. The wires and plugs are pretty new. The coil I couldnt get a good test on, so I went ahead and changed it and the cap and rotor just to be on the safe side. Still no better. Then the manual went to the fuel system. I checked the TPS, MAP sensor, IAC, EGR, Coolant temp sensor (which was bad so I changed it out), and still nothing. I took the top off the TBI unit to check and make sure the injectors were not clogged up, and the pressure regulator underneath there was covered in GUNK from someone either using cheap oil or STP engine treatment. I also have an 88 sitting in my backyard with a broken crank, so I swapped out the injector top plate to the 92. This helped a little, but it still was spitting some, so we decided to swap out the injectors from the 88 to make sure they werent bad. Once again this helped a little, but the issue still isnt solved. I think it has to be either the fuel pump or the ECM itself, so I am going to swap ECM's between the 88 and the 92 (if they are the same manufacturer codes) and see if this helps the issue any.

Does anyone have any other ideas? I am just about at the end of my rope with this truck, and don't know much else to try and change out.

Gene

mcreyaufmiller · August 14, 2005

I know that you have changed the plugs and wires, however, double check them. If for some reason the wires are shorting out against the block, then it will cause the condition you described. Just my $.02.

biggene · August 15, 2005

OK we swapped out the ECM today and it was better for a bit, but it is still doing the same thing. My stepson is going to take the truck and have the fuel pressure tested tomorrow and I am going to install new plugs and wires again and see if this could possibly be the issue.

Gene

biggene · August 16, 2005

LMAO Ok I am a big enough guy to admit it, I should have listened to begin with!

After doing all of the above and nothing helping the issue, my stepson and I pulled the bed off, and swapped out the fuel pump. LO and behold, this has fixed the issue.

Thanks to all for the advice, I definitely appreciate it.

Gene

biggene · August 16, 2005

LMAO Ok I am a big enough guy to admit it, I should have listened to begin with!

After doing all of the above and nothing helping the issue, my stepson and I pulled the bed off, and swapped out the fuel pump. LO and behold, this has fixed the issue.

Thanks to all for the advice, I definitely appreciate it.

Gene

71GMC_3/4T · August 16, 2005

Glad to hear you got her fixed Gene!

So, how long did it take you to swap in a new pump?

biggene · August 16, 2005

Including the break for a cold drink of water (temp was aorund 102 yesterday afternoon here 100% humidity), around 3 hours from the time we took the first bolt out of the bed till we bolted the hitch back to the frame. It wasnt really as bad as I thought it would be taking the bed off.

Gene