Hi all.

New here. Got a 1995 K1500 4WD 5.7 liter I've owned for over 10 years.

Apologies if this is already in the forums somewhere but I figured it wouldn't hurt to see what advice y'all might have about an engine issue I've been having.

1. The engine seems to misfire occasionally at idle. It has always seemed to have a misfire problem but would get better whenever plugs, wires, distributor cap and rotor were replaced. I've seen oil on one or two of the plugs before. My brother helped me check compression when I first got it but I don't remember any problem from that.
2. The engine seems to do what I call hesitating or almost stalling during light throttle/low speeds (like through a parking lot or driveway) which might also be misfiring, I'm just not sure. It never stalls completely, just seems to sputter like its going to cut off but then it's like it finds some new fuel or air and keeps going.
3. I can hear a noise from the cab, somewhere inside the center of the dash or firewall that sounds almost like a wind-up toy running. That's the only way I know how to describe it. It's in time with the engine. Mainly noticeable during idle, I suppose driving engine noise drowns it out. Could this be a problem with the distributor or something? It hasn't always had this noise but I've had it probably for the last couple/few years.

No problems starting or accelerating normally.

What I've done so far:
1. Plugs, wires, distributor cap and rotor have been replaced within the last year or two, so I don't think that's a problem.
2. It recently sprung a huge vacuum leak with a loud whistle, throttle body gasket had hole in it, replaced.
3. New fuel filter due to being about 10 years old.
4. Replaced PCV valve and hose just due to condition and preventative maintenance.
(unrelated, just finished completely replacing the entire rear brakes, axle bearings, seals, and obviously diff cover gasket/fluid, due to axle grease leak onto the brakes)

My quick and dirty short term plan is to first:
1. Remove, test, and clean or replace the EGR valve, it looks pretty rough.
2. Run a bottle of Lucas fuel injector cleaner through a tank of gas. I don't think I've ever done that. No telling how much ethanol is gummed up in there.
3. I also think it might have a bad main ground cable somewhere (radio turns off and on.)

What else would you suspect or do besides checking compression? I have access to the Haynes Manual and eAuto Repair/Mitchell 1 DIY subscription.

Thanks! I love these trucks. Glad I got one when I did. Love working on it. I've had people ask to buy it, needs new paint though.

 

your manuals should provide all the info you need. The Haynes must have a section for misfiring.

Did you visually confirm good spark on each plug?

Have you measure fuel pressure and leakdown?

Dizzy caps can corrode quickly. I would check it again and make sure it didn't lose timing.

 

I don't think ethanol "gums". But failing injectors are a possibility.

A good diagnostic scanner can help you big time here. (presuming your truck is OBDII compatible)
It can give you a misfire count for each cylinder, which will help you narrow down the problem.
You could also run an injector balance test to see if any are bad.

 

Thanks. I'm not super knowledgable when it comes to fuel and whatnot. I was under the impression that ethanol in fuel can clog up the channels in throttle bodies and carburetors; just looked it up and I guess that's caused by ethanol dislodging existing deposits. I digress.

The 95 is only OBDI which will still throw some codes but I don't know if it can log misfires. (Haynes manual will know.) I will check the codes again but last time I checked the only code was a problem with the idle air control valve, which was probably due to the throttle body gasket having a hole in it right under the IAC, but I also already replaced the IAC before I found the gasket. (Haven't rechecked codes since.)

I just figured I would make this post to see if anyone out there has had direct experience with these symptoms while I'm waiting for the spare time to mess with it.

 

misfire is a common symptom, but has a huge variety of causes, so you just need to eliminate possibilities one by one.
Since the problems are most noticeable during idle, that makes me suspect more vacuum leaks.
See if your local part stores have loaner smoke machine. That will allow you to perform a very thorough test.

 

To clarify slightly, the biggest problem to me is the hesitation/near stall at low throttle/speed rather than the misfire at idle. I'm just assuming it may be related to the occasional idle misfire, but I'm not sure. Does that move the target any? Thanks for your help.