MSD Coil Problems

[Tony1701]

New Holley 750 carb, jetting was at 72 primaries, been 69 to 74 with no improvement. Changed the carb with a brand new QFSS750, no better. The timing is at 36° total.
I've never seen a SBC that couldn't take anything in the 30° to 40° range total. It's been a slowly progressing issue since we put the 6AL-2 and new coil. HEI was not an issue and ran flawlessly.

UPDATE: New coil is here. It checks out completely different than the one that's suspect, so I'd have to assume that's the issue. Got to install and put this mess to bed. LOL.

[Gaz64]

Did you sacrifice a distributor cap with a large hole drilled in it to check rotor phasing with a timing light?
Digital MSD is more susceptible to rotor phasing, and may need an adjustable rotor.
Coil failure is more likely when the spark has to jump a large gap in the cap/rotor area, before it jumps the spark plug gap.
The HEI is a long duration spark, versus the CDI of MSD, which is a higher voltage, but shorter duration. Gary

[Danny Cabral]

Originally Posted by Danny Cabral Testing the MSD CD ignition box. Points Output - white wire & Magnetic Pickup - violet/green triggering: https://www.msdperformance.com/suppo...ng_techniques/ (Troubleshooting Info) Ensure the distributor's rotor-phasing is correct: http://documents.msdperformance.com/8644_tb.pdf (MSD Rotor-Phasing Document) MSD has a good video on why it's important: http://www.youtube.com/watch?v=aWMlNwGW0tM (MSD Tech Rotor-Phasing Video) For naturally aspirated engines, the rotor is usually phased halfway between minimum & maximum amount of timing advance used. For forced induction engines, the rotor is usually phased at maximum boost retard, because that's when cylinder pressure is the greatest.

[Tony1701]

Well after further inspection, the coils measure identical according to the owner. So I'll entertain checking the phasing next time I get a chance to work on it. Unreal that something so simple could be so complicated. I'm tempted to hot wire am Analog 6AL and see what happens as well. Keep you posted. Thanks everyone.

[Gaz64]

Yes, that's correct, sometimes so simple can be so complicated. Here's one: Flat spot on acceleration only when exiting a left hand corner. One would think carburetor related, but ended up being a ballast resistor broken, and would go open circuit on LH turns. Gary

[Tony1701]

Phase was perfect, distributor cap & rotor were a little funky, and inside the distributor was real rusty. How & why I don't know, as it's parked indoors and no washing of the engine compartment ever happens. Changed the cap, rotor & pickup and seems like the problem has disappeared for now.