Gurus - help me diagnose a no-code miss
I have an LT1 in a caprice wagon. New optispark, new wires, engine is not throwing ANY codes at all. However, I feel a distinct miss throughout all RPMs. At idle, under load - it doesn't matter. Car starts right up - within 1/2-1 rev of the starter. Idles with just a touch of a miss - every revolution without fail. Engine appears to idle well if you're looking at it, but if you put your hand on it, you can feel it.
I JUST bought the car so I am a little pissed.
Vac reads 18.5 at the manifold. All the plug leads are carrying spark. There were a few vac leaks at the mani that I took care of. Replaced the PCV. Tightened the manifold down - some of the nuts were borderline hand-tight. No ticking or knocking to speak of.
Initially, I thought it was a resonance/harmonics issue with the dual flowmasters not having any sort of h-pipe, coupled with the fact that the dolt who installed them didn't use isolation mounts on the rearmost section. However, at a very low cruise RPM, just strolling along at about 35 and in a high gear, you can feel it "chug, chug, chugging" along.
The miss is dead-on rhythmic. At this point, I am thinking it may be a fueling (injector) issue or bad plugs.
Thoughts? In the past, if I've borked up the firing order, a typical SBC will barf out of the intake or pop though the exhaust, so I don't think that is the problem. I'll be checking anyway when I re-do the plugs.
O' LT1 gurus of the forum, I seek your guidance...
Last edited by AtlantaDan; 10-11-2011 at 06:21 PM.