another egine miss

[Pvt Parts]

I changed motors in my Corvette once and had the same problems. Turned out that the main battery cable nut on the starter lug had not been tightened. All power for the vehicle, ign, etc came off of that terminal. Tightened the nut on the lug and fixed the problem.

[buzzinhalfdozen]

Randy I'm not familiar with the Mallory stuff, however I would assume that it would work . The "box" is simply looking for a trigger input. What is your battery voltage doing when it acts up? Is it stable, is it above 11.9 volts? BTW you stated that "the computer showed it" (the miss) how exactly did you see the miss? The fact that the tach jumps around when the miss is there would indicate that 1, the tach could be the trouble,2 the "box" is recieving undesired triggers, which causes it to lose track of when to trigger the coil. I would simply hook up my MSD tester to the crank trigger connector and spin it up, by doing so you can ensure the box and coil are OK. What sort of airgap do you have on the crank sensor? Too wide tends to cause issues, over .060 seems to be the limit, also crank wheel runout can cause the same thing, is the crank wheel running true? Please let us know what you find out, as we seem to have a few strange misses going on this forum with no fixes yet. Good luck Joe afew things to consider also, if you purchase a new crank sensor please consider getting the "shielded" sensor. This has fixed more than 1 car that I know of. Also is the miss RPM sensitive...does it start at a given RPM?

[FED 387]

1-some Mallory coils are not compatabile with MSD boxes
2-twist your pick up wires to avoid picking up RF signals in the area
3-get a shielded pick up
4-check for proper air gap on sensor to trigger wheel
5-check spark plug gap
6-check for a bad spark plug
7-check points gap in distributor if using points/check the points wire in the dist- shield it
8-double check MSD wiring make sure you do not have a wire incorrectly installed
9-check battery voltage
10-check all grounds
11-check spark plug wires for break/burns/loose terminals
these are things I would look at and not necessarily in this order either
seems like you checked all the mechanical possibilities so it might be electrical , not knowing what your setup is its hard for any of us to pinpoint what might be causing the misfire

[randy wilson]

Thanks guys, I"ll try to explain what's happening to the best of my ability. I'm electrically challenged in my ability to say the least. Plug gap,0.35, trigger gap, 0.48, new wires and plugs after first run, misses when you make the gear change in every gear, and starts missing again at the top end of fifth. Spikes on the printout is what I meant about computer showing it. I forgot I had a msd tester because I just used it once. Will drag it back out and see what I find. Never, ever, missed a stroke with 4 other engines, and it just caught me unprepared.

[randy wilson]

Also battery never dropped below 12, have 2 optimas in.

[Arnold Greene]

Have you checked/changed the high side chip? It may be hitting the rev limiter.

[randy wilson]

Arnold, it's on the low end of the gear change right after engagment, with a clucthless. From about 7,500 to 8,200.