Hi all,

I'm hoping someone can diagnose my problem.

Background: 1971 Plymouth Satellite, big block. When I bought the car, it already had an MSD 6AL box, plus an MSD Adjustable Spark Timing Control box (controlled by a dial in the glove box). It has a re-curved (by FBO) Mopar Performance electronic distributor, with limited centrifugal advance (20 deg initial, 34 deg total, all in by 3,000 rpm). This was all done by the previous owner, and everything ran fine when I pulled the old motor in June 2016. In the meantime, I've had a new 440 built for it, and installed this same distributor in the new motor.

Today, the new motor was finally on the dyno stand, and they could not get it to run. The dyno owner also has an MSD 6AL box, to which he attached the two leads coming out of my distributor. They were able to get the motor to fire occasionally, but then the spark was very weak, and it wouldn't keep running. Since this same dyno/MSD setup just successfully ran a GM motor yesterday, the dyno owner and my builder believe the problem is with my distributor (I disagree). I connected a multi-meter to the two distributor leads, and I'm getting signals when I spin the shaft - that is, the magnetic pickup seems to be working correctly. Is this a definitive test? Or should there be a certain voltage running through the pickup? Is there a better test for it?

I'm not an ignition expert, but my understanding is that the magnetic pickup is basically an on/off switch that tells the computer when to fire the spark, correct? Is there any way a defective pickup could cause a weak spark?

Any suggestions or other thoughts as to what could be happening would be greatly appreciated. These are two experienced guys I'm dealing with, so I don't want to insult their intelligence - but at the same time, most of their experience is with Ford/GM stuff. Thanks.

Roger

Check the gap between the reluctor and the pickup, it should be .008". about the thickness of a matchbook cover. If it's too far away the signal gets weak, and no it's not on/off. The MSD may not be getting a strong enough signal to fire consistently, which sort makes sense with your comments. The signal is also polarity sensitive, swap the leads and it will not fire properly if at all.

A drawing to verify connections

Thanks, I forgot to mention that they did try switching the leads. I also verified that he checked the gap between reluctor and pickup.

On a side note not sure how much cranking can be done before the lobes need regooping. As said check/confirm connections (wired correctly & good continuity). I would use that dist out of the eng or a spare one (even a /6 one) & spin it by hand & see if you get good sparks out of the coil wire to confirm you are set to go.

Thank you, Robert. I am also concerned about all of this cranking - I wasn't there so I don't know exactly what went down.

I did find two additional methods to test the pickup:

1. Hooking an ohm meter to the leads should register between 150-900 on a Mopar electronic distributor. Mine reads 284.

2. In addition, grounding one of the leads against the distributor body, and the other to either pickup should show nothing registering - if it does, the pickup is bad. Mine showed nothing.

I'm beginning to lose faith in these guys not being able to diagnose a simple ignition problem, and am thinking about just bringing the motor home, installing it in my car, and doing the break-in there.

If you are worried about all the cranking...take the distributor out and spin it by hand until you start seeing sparks...

I dont know for sure how much cranking can be done safely & not wipe the lobes but cam failures are epidemic & I wouldn't have faith that they woulda stopped cranking to check their handiwork as opposed to continuing to crank (it'll fire any second now!) especially since the diagram Supercuda posted is widely available & you'd think they woulda checked all of that ahead of time (since an immediate fireup is critical).