Turbo LT1 weak spark / ignition issues
Huge misfire issue under boost, tried lots of stuff, still no success, not sure what to do next. Sorry for the long post . . .
Car had been sitting for a couple weeks or so, when this problem just came on out of the wild blue sky. Prior to that, I had no apparent spark energy issues - she would hold strong at 14psi with water meth as well (stock lower end motor also!).
So, went to drive the car, find out that it misses badly etc at anything over 5psi. Pulled over, and car actually had trouble restarting at the time. Hmm odd. Car runs OK , maybe a slight miss detected, but mostly OK until misfires and carries on badly at about 5 psi, consistently. (also turned off water meth to see if that was operating improperly, and no effect was seen)
So decided not to go on the next day's roadmeet (bummer) and fix the system before it leaves me stranded somewhere.
Car already has upgraded MSD cap/rotor, stock OEM opti crazily enough, and upgraded MSD plug in coil, installed in Oct. 2018.
ALso new Taylor wires a few months ago.
Plugs are now gapped at like .021" I believe it is. Had to go there when I turned the boost up.
Got to really working on the car finally this weekend to see what's really wrong. Was thinking the cap/rotor was likely the issue, but decided to do more checking before blindly pulling the opti.
So I find that using my adjustable Lisle spark checker on the coil wire, that I only get 1/4" or so of spark, and it's not real consistent and looks kinda weak. Last year when I did the work originally, it had blue thunderbolts and an audible snap at over 1/2". Hmm. (opti isn't even in the loop at this point of course).
So, I seem to have weak spark from the coil. Go through the factory manual - checked the terminals at the ICM, and getting good ground, and also showing 11.5 volts at both the wires that come back from the coil. So all that checks out - and the manual basically says replace the ICM.
So I replace the ICM, and no real change, except that somewhere along the way of testing the MSD coil has failed to produce spark at even 1/4". Now that's odd, - so I try the old original LT1 coil (knew I saved that for a reason), and how bout that, I have spark again. I start to widen the gap on the spark tester, and was able to get to about .350" or so, not stellar by any means, but the spark looks better anyway. Still not a real great reading it seems. So I can't believe it, and swap back to the MSD coil, no spark again. Swap back to original - spark comes back. Ok, guess the MSD coil is dead, although the DVM says otherwise - no apparent open circuits in the coil - but there must be more to it to properly test I guess.
Also took the ground post nut loose, cleaned the nut and the ground lugs, and put that back. No change to spark energy.
So kinda decided that maybe the MSD coil had gotten weak - so test drove the car with the old original coil (knowing that the spark still doesn't look very good, especially when testing at the plug wires) and of course it has the same result. Will not run good at all above 5 psi.
I'm fairly sure it's a spark issue, kinda acts like when your plug gaps are too wide and starts blowing the spark out - I know what that feels like, and this seems to be close to that.
Checked voltage at ICM plugs, replace ICM, swap coil, clean grounds, problems still exist???
So - any thoughts out there?
91 Camaro Road Race American Iron car - The Menace
91 Camaro RS - '93 LT1/T56 swap project, 10.5:1, 224/224 @.050, 60lb Deka, home ported heads, 78mm Vs Racing, intercooled, 2 bar MAP tune on $DA3
Last edited by Jeremy Moen; 11-23-2019 at 02:15 PM.
Reason: add more stuff!