another egine miss

[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.

[FED 387]

when u say trigger gap do you mean the wheel on the crank?? if so it should be at least(from what I've been told) .060 to .080-- the more gap you can run the better do not know why but what I always was told--- big block engines especially ,the cranks flex at higher rpms closing up that air gap !!!! have you tried twisting the wires on the pick up??? the full length this can help with RF interference

[buzzinhalfdozen]

Randy, yes get out your tester, lets look at the easiest stuff first. Though there is an almost unlimited list of things that could be causing your issue I like to start with the simplest things first. The tach and datalogger both showing eratic engine RPM in my mind indicates an ignition issue. Posts indicating interference are of interest, any signal getting into the box can cause problems. Have you changed the routing of any wires on this car? Alts. fans,coils ect. too close to the trigger wire can "leak" into the wires. Twisting the wires is a good idea though most are already twisted. Joe

[randy wilson]

Thanks guys, and will try all til I find it. Been busy with the business, and Steve just moved to a new house and farm, and has a beautiful shop on it, and that's where the car is sitting now. It's so hot, we don't feel like going to Eddyville, but when we do, will let you all know. Can't be that serious, but can sure be frustrating. Too hot to race. Heat never bothered me when I was young, but now it's a big deal.

[BlueOval Ralph]

Could either be lean or rich at that point in fuel curve , don't forget at the bottom of the gear change you have just had a big change in booster draw.

Originally Posted by 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.