MSD minimum cranking rpm

bfunk · Jan 29, 2017

A friend of mine switched to a 6al and has no spark. If we pull the distributor and spin it by hand it makes spark. We have double checked everything and even swapped out module and distributor out of my 440.
This is a high compression hemi with stock starter.
My 440has a mini starter
I'm thinking the stock starter just doesn't spin fast enough. I've read other posts on this but nobody posted a fix.
Am I barking up tthe right tree?

bfunk · Jan 30, 2017

Nothing, I think we'll install a mini starter and see if,that works. I'll update post when fixed.

dieseldazzle · Jan 30, 2017

Is the distributor spinning when installed? You pulled the cap to make sure? Weird issue

Mike67 · Jan 30, 2017

I don't think the box cares what rpm the distributor spins... It discharges based on an open close signal from the pick up....
Maybe way out of time...???...definitely odd....

Jeremiah · Jan 30, 2017

What is the battery voltage when it's cranking? I don't think the starter is your issue here. Do you have spark at the plugs when it's turning over?

Did you tie the "start" and "run" circuits together with the little red wire to the MSD box? If you had one connected and not the other it will act like a bad ballast resistor (fires up in "start" key position and dies when key returns to "run") or it will have power to the MSD when the key is on (probably how you were testing when the dist. was pulled, eh?) and no power when cranking.

More or less you need to eliminate (or bridge) the ballast resistor if it is still in service.

bfunk · Jan 31, 2017

Thanks for the replies!
Cranking voltage is about 11 volts, checked for voltage to module during cranking, battery voltage. Checked for voltage to positive coil during cranking, ok, no pulse on negative side.
When I pull distributor and spin it, it won't spark when I turn at slower speed, which makes me think it may need cranking issue.

Ranger16 · Jan 31, 2017

bfunk said:
Cranking voltage is about 11 volts

Fran Blacker · Jan 31, 2017

Coil didn't cook ? Did you up grade to a MSD Blaster?

Jeremiah · Jan 31, 2017

Good question on the coil. I have cooked Napa brad coils with a MSD 6AL.

It sounds like you have enough cranking voltage that it should have spark.

The next test is to see if the box is triggering by unhooking the distributor pickup wires and while observing the coil wire near a good ground (key on, coil wire away from fuel/fumes!) touching the WHITE (points trigger) wire to ground should make the coil emit a spark. If this does not work you need to try a different coil, check the magnetic pickup, or try a different box.

Fran Blacker · Feb 3, 2017

bfunk said:
Thanks for the replies!
Cranking voltage is about 11 volts, checked for voltage to module during cranking, battery voltage. Checked for voltage to positive coil during cranking, ok, no pulse on negative side.
When I pull distributor and spin it, it won't spark when I turn at slower speed, which makes me think it may need cranking issue.

You get that puppy running?

dvw · Feb 5, 2017

Where is the box voltage being picked up? The blue wire for ignition goes dead in the crank posistion. You need to tie the dark brown and dk blue from the ballast feed together
Doug

bfunk · Feb 10, 2017

Its been too cold to work on it lately. We did hook heavy red and switched red directly to battery. And also hooked ground directly to battery. I haven't tried grounding the white wire yet. I will try that when it warms up. Thanks again!

bfunk · Jul 12, 2017

Just to update this post, we did install a mini starter and it fires up. I know of several mopars that the msd works fine with stock starter, unsure why this one is different. The original starter seemed to turn over normal speed.

MSD minimum cranking rpm

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