For the last 8 months now I have been having a "phantom" misfire. Cylinder 5 will start misfiring, service light blinks...stays on. I have taken it to 2 different mechanics and they can never find anything and then a few days later it mysteriously goes away, only to return in about 2 months. Its a 99 5.3L. 88k miles Has anyone ever heard of this?

went back to stock plugs, wires,
hypertech pp3 (misfires with stock progarm also)

Thanks in advance.

 

You might want to get you ignition coil check out, could have a winding problem.

 

Unplug injector #5. Take the white plastic part out of the wire clip. The two metal contacts inside the plug need to be squeezed together. When you slide it back on the injector make sure it feels nice and tight. I had this same issue, SES codes, misfires, baffled mechanics. It was the damn electrical connection! The plug will show 12 volts and a ground but if it isn't making good contact with the injector, it misfires. Comes and goes with heat, or it did on mine. Helped a guy a few weeks ago on here with the same issue. Give it a shot, only takes 10 minutes and it's free.

 

Did you figure it out? Read this as well.

https://www.performancetrucks.net/fo...d.php?t=348369

 

1Slow has some good info.
One other thing if the injector checks out, the 99-00 Silvo's had issues with the knock sensor programming. The PCM would pick up harmonics that were translated as knock and trigger misfires and retard timing. I can't remember if there is a TB for it, most went to an 02+ program.

 

well i wish i could give you guys some more information. The miss solved it self between the post and replies. I checked the injector connection and was missing the little grey piece. Im guessing one of the mechanics must have checked this out. I tweaked the wires together and hopfully it wont come back. I have heard alot of bad things about the programs on these 99's. Where would I go to get a newer program? Thanks again.

in regards to the previous post I could deffinitly feel the miss.... then hits again all on its own. light stays on... eventually goes away and does not come back for awhile.

the only other code I have gotten other than a p0305 is the random cylinder misfire code only once.