TimmyZ28

I've been trying to diagnose and figure the problem out but still acting up. I've finally done some searches and all the threads I have seen, I've either diagnosed or replaced already. It's a 96 z28, m6, H/C/I, 30lb injectors, the usual. When it starts to warm up, it breaks up at low rpm under a load, but when I get on it, it seems to wake up. I also started to notice at 2800rpm or so, the exhaust note/tone changes and that's when it picks up.
-cap and rotor replaced 2 weeks ago with MSD since I broke my old one getting it off
-fuel pressure good at turn key, start up, idle, and under load
-fuel pump and fpr replaced last year (no fpr leaks at vacuum hose) granatelli pump
-all plugs look good, same gap, no abnormalities, also replaced last year, ngk
-all wires ohm out good, none burnt, all are wrapped with heat shield since I've burned way too many, replaced last year, Taylor wires
-icm and coil replaced last month, accel coil, GM icm, both spaced away from head
-injector spray patterns good, none seem to drip, replaced when build was done 2 years ago, accel 30lb
-wiring from PCM to icm ohm out good, opti wiring ohms out good as well
I'm just looking to see what people have run into and maybe can lead me in the right direction. I work on newer Chevy and Cadillac cars everyday and it may seem funny, but only being 22, it's alot easier diagnosing things on newer cars with more modules and electronics than older cars lol no CEL also

noice

It is your cap and rotor, I had the same problem. Car would buck and stumble at idle and off idle. Once above like 2500 it would come on strong. I put 104 octane in it and it seem to lessen the problem.

The real problem was the MSD Opti, the cap for whatever reason melted the traces that go to the back of the rotor. The front of the cap was melted a little and it was having to jump across a gap just to get to the rotor. The MSD unit was brand new $500 job. I think that it was either a piece of crap or I pulled too much vacuum into it and flexed the front cap into the rotor.

I pulled the old opti out and hooked it up to the car and spun it by hand and saw the spark sucked coming out of it. Hooked my other spare opti up and it ran great again.

TimmyZ28

I originally wanted to just pull the cap and rotor and clean the contacts, but I broke the vacuum tube off so I went ahead and bought the MSD cap and rotor. It's only 2 weeks old, the opti itself is about 4-5 years old. I have my old, old opti that came on the car when I bought it 6+ years ago. Maybe I'll pull that out and try it.

BALLSS

look VERY close for any arc at plug boot. if you can't see every inch of the plug boot you need to. jack up car and look from underneath also. in a dark enviroment.

this does not cost a dime and in many cases is the issue...even if you have replaced "plugs & wires"

TimmyZ28

I checked for arching with water while it was running. That's the trick I usually use but I'll do the dark environment as well. At this point, it doesn't hurt to check everything.

TimmyZ28

Update:

I think I may have figured it out, but not 100% until I perform the repair. After some brainstorming for a while, I realized that it seemed like the car would break up on the low end when in closed loop. So I unplugged both of my pre-cat O2s and drove the car in open loop for about 15-20 minutes. Not once did I hear it or feel it break up. It wasn't all there since it was running on a predetermined fuel trim being in open loop but it wasn't breaking up. I'm going to buy two O2s tomorrow and see how that goes.

TimmyZ28

Put the new O2s in and once it goes into closed loop, its still acting up. Good news is I'm buying a complete L92 6.2 out of a 2007 Escalade for $500 tomorrow. Finally, my long-awaited LS sway will finally happen!