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Wedge MSD6 in a TR8 question

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philman

philman

Jedi Knight
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Took my DHC out to the Muffler shop today. First time out of the shop for 3 1/2 years. At about 3k-3.5k RPM the tach zeros out and the engine starts missing. Runs great otherwise. I can idle for ever without any problems.

I am running MSD6 to a Mallory Unilite Dizzy. Is there a point in the RPM curve where the MSD box switches circuits? If so, could I have a bad high RPM circuit?

Otherwise, no bad noises or strange phenonema was noticed.
 
No, the MSD has only one "circuit." It is capacitive discharge with multiple sparks but honestly above 3k or so the plugs are firing fast enough that the multiple spark discharge doesn't do you much good.

When you get that kind of issue -- miss at higher rpm and the tach needle playing games with you -- my experience has been you either have a pickup (in the Unalite) going bad or you are grounding out somewhere. Last time it happened to me was the coil wire -- developed a crack in teh boot and was arcing to the hood. Check your wires and see if Mallory will sell you a new pickup for the distributor.

I bet it is the wires though.

philman said:
Took my DHC out to the Muffler shop today. First time out of the shop for 3 1/2 years. At about 3k-3.5k RPM the tach zeros out and the engine starts missing. Runs great otherwise. I can idle for ever without any problems.

I am running MSD6 to a Mallory Unilite Dizzy. Is there a point in the RPM curve where the MSD box switches circuits? If so, could I have a bad high RPM circuit?

Otherwise, no bad noises or strange phenonema was noticed.
Click to expand...
 
I have the MSD6 on mine and have been very pleased with it for the past 8 years. MSD has a policy that if it goes bad you mail it in and for I beleive $30 they fix and clean up the unit. I had to do that when I first got my 8 and they cleaned it up, fixed it and mailed it back in 2 weeks.
 
But when the MSD goes bad (simple test for it, you cross a wire and look for spark, but can't remember the actual sequence off hand), the car just ... does....not ....run.

Intermittent stuff, I bet you have a wire going bad, or the pickup module. Those have been the source of my irritating intermittent misses.
 
I wired the power to the MSD box through connectors; do you think that the connectors could be causing a problem at higher rpm's by limiting the current through the wires? Maybe I should be using power connectors as used in ham radio equipment instead of molex conectors.
 
I think the high rpm miss is a mis-adjustment of the distributor timing, and the tach issue is unrelated. I have a tach adapter, I just didn't install it; but after getting the exhaust system in I could hear myself and when the tach zeroed the engine was missing, not going dead. I adjusted the timing and this weekend will install the tach adapter. Now for a road test.
 
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