[73LeMans]

Originally Posted by Scott65

How is your shielding grounded? Or is it? Shielded cable should do what you need, but it needs to be grounded on one end (only).
And... are the grounds for everything else good, and to the battery or engine block/head?

No kiddin? Hmm, learn something new every day. Thanks! Shielding is definitely NOT grounded. I'll make that happen and report back. Rest is good - The ground circuit for the pump AND controller has 1.6 Ω resistance, connections are tight and all the crimps are good. Battery is new, ground cable is 1ga and is also new. Just to eliminate any question, I ran 10ga power and ground feeds direct to the battery for testing. What I've descried above happens with those wires in place, and slightly worse without.

Originally Posted by rod cole

Can u take the tack signal from the ground side of the coil ? Or at least watch it with a test light to see if it is stable there. I have never seen a good MSD box they all eventually do weird **** send them in. No problem found but the problem goes away for a while.

Tried to get a good signal from the distributor but couldn't find a good one. Agree, the little red box is a mystery! Hate to throw parts at it, but if its done doing what it needs to do, I'm OK with getting another, although I doubt they are made as good today.