01pewterz

ok i've been trying to figure this thing out with no avail, (for 84 silverado in sig) at around between 35 and about 50 mph, (could be others these are the speeds I run the most) it has stutters no while on the gas but when you hold it at speeds, you feel it kinda slightly bucking but can't hear a noticeable mis, then if I floor it, its fine til right before it shifts it starts mising and blows black smoke (obviously fuel). I know when my pcm was retuned it was set for 6000rpm shift. Any ideas, could possibly a bad cat be causing this? Or maybe a bad injector?

01pewterz

just pulled my plugs and checked em and the back 4 (5-6-7-8) plugs are black while the front 4 are still nice and clean, this is part of the same problem i've been having for the last couple of weeks, and within the last 2 weeks I changed plugs and rotated my injectors 4 front to back and vice versa to try to fix the issue along with changing both o2 sensors. Any ideas???? Could this be intake related or opti???

Z28Freak86

just to get you started in a direction, i would go over the ignition wires. off the opti, there is a ignition coil wire, and if that wire gets frayed or exposed in anyway, it could cause your symptoms. just an idea that doesnt hurt anything. but its weird that its located in the back 4 cylinders....

01pewterz

yea i thought so too, thinking it may be intake related but if I had an intake seal issue in the back i figured they would lean instead of richen and I went over the wires and they seem fine, checked for routing around headers (which could still be the issue) and looked for a light show at night and didn't see any arching. And since this is only about a month old build the opti was newish (replaced late last summer and only had a few miles on it when top end was rebuilt) and I did the opti prevention things (locktite rotor screws and rtv cap). So I don't think its opti? Kinda started leaning toward my msd box, any ideas???