Misfire in a 99 4.8 Silverado

rally2 · August 27, 2003

I have a 99 Silverado that has a continuous misfire. It started off with not wanting to start. I read through past posts and found that the fuel pressure regulator can cause this. Sure enough it was bad. I changed it out and I now starts and runs fine but it is still misfiring. I can feel it at idle and then the SES light flashes when going down the road.

Things that have been replaced tracking down the starting problem were new fuel filter, plugs, cleaned injector, and replaced fuel pressure regulator. So I guess that leaves coil wires and coil packs. The wires appear to be fine and I see no arcing but who knows. The code was multiple misfires but it did not say which cylinder. I think they were using a cheap code reader so it didn't go down to enhanced code level. When I had pulled the plugs #4 was pretty nasty compared to the rest. The truck has 57,000 miles or so.

Any ideas would be a great help.

Thanks

rally2 · September 2, 2003

Uhh anyone anyone.

toddgotfish · September 3, 2003

may sound dumb but

check to make sure you got the right plugs

coil packs hardly ever go bad

wires would be cheapest next try

any bad ones could easily be seen at night

check to see if any metal has gotten into the plugs down around the ceramic

and last but not least

if you used ANY type starter fluid it will ruin these plugs

it seaps into the ceramic and will foul them out often

let us know how it comes out

Cyclic · September 3, 2003

My old truck (2001 4.8) did that also. Wound up being a bad ground/loose connection on the coil packs. Simple removed and unplugged them. Then lightly cleaned the bolt up points and treated all connections and grounding points with di-electric grease and reinstalled. No more problems.

rally2 · September 8, 2003

Thanks for the feedback.

I thought back to when the problem got really bad. When the regulator was bad it would do it now and then but after I replaced the plugs it got even worse. So I went and got the standard replacement AC Delco plugs and it runs like a champ now.

I guess the moral of the story is don't use cheap plugs.

Thanks again for the help