Looks like a great set of people offering input here. First post.
At my wits end with my 1999 GMC Yukon Denali 5.7L R code @ 215k miles. I am hoping for a simple solution.
Here is a quick and dirty, truck from Georgia great shape, rust free, got from a friend that did oil every 3-4k, and regular maintenance on time with records. It’s eating distributor caps every 2000-3000 miles. (have pic but couldn’t figure out how to post it yet) He had the same problem, I’ve owned it for about 3 years now and have changed cap and rotor about 6 or 7 times in 20k miles. Thankfully I have a lifetime cap and rotor from AutoZone but I’ve used several brands, including AC Delco, no change in results.
Here is what I’ve personally changed in the last 3 years related to misfiring, roughly in order, vacuum leaks, Fuel injector spider (Upgraded AC Delco unit, original was toast) AC Delco OEM iridium spark plugs, Billet distributor (didn’t realize it had already been changed to aftermarket distributor) Autozone gold spark plug wires 2X (replaced fairly new set of AC Delco wires that I think were better but trying to rule everything out) Autozone Gold Distributor Cap and Rotor 6X (lifetime) AC Delco coil (replacing a holley coil) and ignition module…still after a few months it starts misfiring and the cap looks like the pic.
Thinking there must be moisture getting in, I tried using a little RTV to seal the cap to distributor, tried coating inside of distributor cap very lightly WD 40, I’ve read every blog and posting about these old 5.7’s misfiring. P0300’s if I let it go, and sometimes it clears itself in a day or two but comes back so I just swap out the cap.
Short of changing the cap and rotor every few months which isn’t a deal breaker, I’m out of ideas. With each new cap it runs really great, smooth and strong @ 215k.
I am wondering if it could be an electrical issue….bad ground? Contamination into distributor?
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