MSD 6A ignition

[FastWoman]

(deleted duplicate post)

[70 Cam Guy]

I didn't know these came in different varieties. How do they differ from each other? Mine was a $16 part from CarQuest.

Honestly I don't know if there is a difference. Do the modules control dwell too? Maybe that can change but I wouldn't be surprised if they are all functionally the same. I was just highlighting how cheap you can get the modules for and you found one for super cheap! I really would carry a spare though. They don't normally give you any symptoms of impending failure. The engine cuts out and you're stuck.

My dad carried a spare for years and never needed it until a few months ago. His tool truck cut out in the Caldecot tunnel and he coasted to the exit and pulled off. He replaced it and was on his way like nothing happened.

[FastWoman]

I think I read that some of the modules have a longer dwell to better saturate the coil. I'm wondering if those would be better suited for lower RPMs, though.

Thanks for the advice about carrying a spare. I think I'll do that!

[alhbln]

This post is a bit too late to help but just for the record The EFI requires a single kickback impulse per spark from the inductive coil setup to trigger the fuel injection. The "kickback" impulse from the coil is the reinduction from the magnetic field, a peak with about 100-200 volts (depending on the coil ratio and setup). You can see this quite nicely with an scope connected to the primary side using a probe rated for 500 volts.

For setups with electronic capacitive discharge ignitions (such as the MSD 6A) there are adapters which turn the +12V square wave tacho trigger impulse from the MSD or ignition box into a high voltage kickback impulse by means of a small transformer. I believe the correct MSD part is 8910.

The primary coil impulse(s) from an MSD setup cannot be used as you have multiple sparks up to 3000 rpm which will not work with the EFI (which expects a single trigger impulse per spark).

[FastWoman]

Better late than never. Thanks!

FAIW, I think the MSD's multiple sparks occur in such rapid succession that they would not multiply trigger the ECU. At least that's my theory.