I acquired a 1979 Minnie Winnie with a 440 in it.

The #7 cylinder is dead, despite having good compression (130) and fire.

The #5 cylinder has only 50 psi, but I've isolated that to a bad exhaust valve or seat. I'll know when I yank the head.

But this #7 cylinder really has me stumped. My mech diagnosed for hours and shook his head. He said he has never seen an engine with 40-45 degrees of dwell and he has not worked on a Mopar big block in a long time. His scope says fire is getting to the plug.

He says it could be the EGR, a vacuum leak or both. He says rebuild the Thermoquad, replace the intake manifold gasket, check all the vacuum lines and hope it works.

Any Mopar Masters out there know what is causing this?

The engine has 40K miles and this Minnie Winnie sat in the hot San Diego sun for 9 years. They all said it ran perfectly when it was parked. I believe them and the old spark plugs confirm their claim.

 

how do you know thers fire to the plug? doesnt a O-scope just tell you theres fire in the plug wire. what plugs are you running?
this is me. i have problems with ngk and champion fireing under compression
autolite has never failed me.

 

Autolite is precisely what I have in it. I took an old plug, broke off the electrode and started the engine. I lowered it to a bare metal spot I sanded on the valve cover. At 1 1/4 inches away it started snapping a blue and red arc.

My guess is that is sufficient juice for it to fire under compression.