95 K1500 350 - Miss/hesitation problems for past 2 months

[RHamill]

It's the plugs probably, my friend did a plug change in his 97' Bravada because MPG was dropping, then it started missing like a son of a *****, plugs were gaped correctly, just didn't go deep enough, or something of that sense.

He took it in, got some different plugs and it's ran fine ever since.

 

[95_1500]

Well guys i hate to bring this back from the dead...

The problem seemed to subside enough that it was tolerable. It still had some finicky stuff going on so I concentrated on my fuel, while checking fuel pressure I found with ignition on engine off that my pressure would drop from 12psi to 0psi about 10 seconds after the pump quit priming. Found i had a leaking injector. Replaced them and the regulator and it ran great, shifts smoother with no hesitation. Now if I start it cold it idles and drives off just fine. If I turn it off for 10-15 minutes and start it back up the idle will fluctuate from 800 down to 700 ish for a while and if I try to give it gas it feels like its missing. Once I get above 10 mph or so it smooths out and runs fine, come to a stop and it doesnt have the fluctuating idle. Started it today after about 45 minutes of getting home and the first time in 16 years it died right after cranking, started it again and it had the fluctuation but didnt die. Left work tonight and no problems.

Im thinking the off fuel mixture might have fouled one or more of my plugs and when theyre warm it affects it. Wanted to get some opinions before buying a new set of plugs but that is my starting point before I tear down the whole ignition system. Might replace the pick-up since its the only thing I havent replaced in the last 4 months. Starting with this before I drop into the ignition or fuel pump relay and eventually the fuel pump.

 

[MOBS]

Well, it is getting about time for your 100k mile tune(replace everything that makes it go vroom).

 

[95_1500]

Yeah I have practically covered that.. Tore down and checked the whole ignition system and all is good. Found an old forum post saying the screen in the fuel tank was badly clogged even though the pump was pushing 13psi like mine. Looks like im dropping the tank after work tomorrow. Even if it is just the screen I might as well replace the pump since this one is 16 years old

 

[Chris]

Sounds like the pump is dying. Mine did that for a month before finally quitting.

 

[sewlow]

16 yrs. out of a pump? Wow! I've had my '98 GMC 7 yrs., & have replaced the pump 2X in 230,000 K.'s. One lasted 60,000 K. The original went 140,000 K.

 

[MOBS]

Yeah, still had the stock one in my 95 when I started tearing down for redo....had 198k miles on it and still going strong.

 

[95_1500]

Well guys, I was hoping this would take care of it but the fuel pump did not change the issue. The truck sat for about a week due to me not having a lot of time to work on it and dropping the tank fought me the whole way and upon first start up it ran decently and took it for a drive. Got back home turned it off for a few minutes, started it again and its back.

Its been about 5 months since I last tested my EGR and I have since done a top engine fuel cleaner as well as the new injectors and regulator. Going to do the EGR vacuum line test within the next few days and see if it makes a difference.

My thought is that if my exhaust has a slight restriction like I suspect, a stuck EGR would cause a constant recirculation of high concentration exhaust emissions causing this stumble at idle but once up to speed the engine is able to push more of it out of the exhaust thus smoothing it out.

 

[shortchevy]

check your intake mani gasket... take a can of carb clean (has to be flammable) and spray it around the mating surface of the heads and intake manifold... pay attention to the idle, if it raises then your gaskets bad... its a shot in the dark but without seeing your truck run this is my 2 cents. the gaskets prolly fine but checking is cheap... also, did you replace the fuel filter?

 

[95_1500]

This has crossed my mind recently as I came across it in my research and I will go ahead and check for it. I replaced the fuel filter shortly after all of this started around January/February.. I am certain it is not a lack of fuel problem. If I dont make any headway checking the EGR and intake gasket I will go back to the sensors. I still have the stock IAC and CTS and I will do the voltage check for my MAP sensor although it was also replaced.

If none of these turn anything up my last resort will be the ECM, i've seen that when they start acting up it can cause issues like this without triggering the CEL.