98 Chevy Silverado Fuel Pump goes in and out. Also won't idle(tries to die)

[oregon712]

Hey everyone, I'm Sean. I have a 1998 Chevy Silverado K3500 4x4 7.4L with 106,500 miles on it. I bought it used in Texas(Had 95,000 miles on it when i picked it up). 1. The problrm is the Fuel pump won't work from time to time, it always works when the truck is running(doesn't cut out then), but when you let it sit for an hour or so, the fuel pump won't work. I took it to the dealer, but as usuall it won't act up for them. lol. 2. Another thing is she won't idle(tries to die but recovers, and repeats until finally dies or is warmed up) when it either sits for awhile(2 or so hours) or is cold. runs fine after warmed up. anyone have any ideas for either or both problems? Thanks in Advance, Sean P.S. feel free to just throw anything out! It'll help.

[2000CAYukon]

When you say it won't work, do you mean that you don't have the correct fuel pressure or if won't start?

Your symptoms sound more like a fuel pressure regulator to me. You should do a search on "fuel pressure regulator" in this forum (or Suburban and Tahoe) to see other posts on the subject.

//2000CAYukon

[oregon712]

The "won't work" is reffering to the fuel pump. The fuel pump itself won't turn on(i can normally hear the pump running). The crazy thing is, is it worked today, yesterday i drove it to work and went to lunch(everything was fine) came back, and then tried to leave an hour later, and the fuel pump wouldn't work. So I tried it again 4 hours later(turn the key to the on/run position, and off again(repeated 5 or 6 times)), still nothing. Then today tried it and it was fine(still has the idling problem). So tomorrow i'll see what it does. When I took it to the dealer a week ago they said the Fuel preasure was at 56 PSI, and that that was within specs. So i don't know. Thanks, Sean

[corning_d3]

Ever tried beating on the tank when it wouldn't start?

[oregon712]

No. LOL(laughing out loud). Next time the fuel pump won't come on, i'll try that. Thanks!. Anyone else have any ideas on the idling problem? -Sean

[profox02]

Had a '96 chevy vortech...have simular symptoms..and replace pump 3 times in two days...after it cut out and died ...without he bed on...we hit the top of the pump and it fired up...later found that the conections were the problem...now it runs fine..

[corning_d3]

My point exactly. C and K series pickups around that year had poor fuel pump connectors, which is why you get a new one with a new pump..

[oregon712]

Well, My Fuel Pump Is offically dead. And the warranty is replacing it. But i'm still looking for answers on my idle problem. When cold or sitting for a while, she idles (lobing, i guess) and tries to die, when it tries to back down from 1000 rpm. she runs great once warmed up, but when cold does not idle. Any Ideas? Thanks, Sean

[corning_d3]

The idle problem could be caused by low fuel pressure...

[oregon712]

the odd thing is that the pump was putting out the right preasure, but the pump would only work when it wanted to. and when you rev the engine up its fine. it only tries to die below 1000 rpm when cold or sitting for awhile. so i wouldn't think it'd be the fuel pump, but it is possible, so we'll see once the pump get replaced. but if you have any other ideas please say them. Thanks Sean

[corning_d3]

Ever checked the vacuum when it was idling rough?

[dr olds]

the fuel pressure was low, it is supposed to be within 60-65psi. i just had the same problem about 2 weeks ago. fuel pressure between 54-56 psi looses pressure when shut off. changed the fuel pump problem solved. truck runs like night and day now. the fuel pressure is now at 64psi and runs real strong. the hesitation is possibly from the low pressure but i doubt it. while the pump was failing my truck also did the hesitation-possible stalling problem. i knew it was electrical so i pulled the plugs...bingo #3 and #7 fouled. what happens is there was not enough fuel for some reason to those cylinders so the plugs fouled, cleaned them and now no hesitation, dead rock smooth idle and no stumbling. (the cap,rotor and wires were already changed 1 yr ago with delco parts), if you need a fuel pump go onto ebay there are 2 companies selling genuine delco pump assemblies for 135.00 with a guarantee(not a taillight guarantee)

[oregon712]

Originally Posted by dr olds

the fuel pressure was low, it is supposed to be within 60-65psi. i just had the same problem about 2 weeks ago. fuel pressure between 54-56 psi looses pressure when shut off. changed the fuel pump problem solved. truck runs like night and day now. the fuel pressure is now at 64psi and runs real strong. the hesitation is possibly from the low pressure but i doubt it. while the pump was failing my truck also did the hesitation-possible stalling problem. i knew it was electrical so i pulled the plugs...bingo #3 and #7 fouled. what happens is there was not enough fuel for some reason to those cylinders so the plugs fouled, cleaned them and now no hesitation, dead rock smooth idle and no stumbling. (the cap,rotor and wires were already changed 1 yr ago with delco parts), if you need a fuel pump go onto ebay there are 2 companies selling genuine delco pump assemblies for 135.00 with a guarantee(not a taillight guarantee)

A shop has replaced the fuel pump, with a new GM fuel pump. And I also had them do a tuneup on it. Had the Coolant temp sensor checked(they say it's fine). And a part(sorry, i don't remember what it was called) that normally puts out 5.0volts was only putting out 2.7 volts. But it still has a problem with cold starts, but still will not cold start idle correctly. anymore ideas? Thank!

[dnelms]

I have a '97 C1500, 140,000 miles. I'm on 3rd fuel pump. Friends with any '97 GM truck product have replaced theirs also.