MSD 6al troubleshooting

Guys, I have recently encountered what seems like a strange ignition issue.
I have a 6al and Msd ready to run distributor.
Car has seen about 600 street miles over the past month with zero issues.
After a short blast today, I was just pulling into my driveway and the car quit...stopped dead. It spins over, but no start.
So I left the car for a couple hours (had a a few things I needed to get done) , came back and tried starting it and boom, fired right up.
So I jumped out, looking around at engine I hear what sounds to me like header gasket leaking. So I go to grab a socket to tighten header, car quits again.
So I carry on and tighten header bolts..none are loose.
So I start looking for loose wires, grounds etc around ignition system, I notice the coil wire on the ditributor cap is not pushed down all the way.
So push it down, boom, car fires right up...no more header leak!!! So I'm thinking ok, maybe that was the whole issue.
Nope...as i'm siting in the car warming it up, it quits again. I fire it up and it runs but the tach starts jumping around sparadically, I have to rev it up to keep it running and every time the tach starts jumping , the engine pulls down and starts missing then clears up, then starts missing, then quits.
No start.
Leave it sit for 20 minutes, fires right up and runs good for 4-5 minutes, then repeats again.
Any body had this type thing happen?

If you didnt run a box i would have said module in distributor .
Had a similar issue on customer car last week , ended up it was the ignition coil . Was a blaster SS coil . Car would fire and run fine cold then as warmed up it would miss and backfire , even pop out exhaust . Initially thought box, but after checking everything tried a spare blaster II . All good

Tex

Thanks for the response Tex.
I am running a blaster 2 coil also. If nothing else, that wil be an easy place to start. I will borrow a buddy's today and see what happens.

As Tex said check the dist pick up also... I had
to change my coil now long ago.. it crapped out

where's the MSD box mounted? Conjures up thoughts of my Chrome box days when I had it mounted on the firewall. It would heat soak and not start. Extended the wires and mounted it to the front of the radiator support and problem solved.

Might Sputter & Die. My exp with MSD

I had problems with mine and it was the tach. Easy to check just disconnect one wire and see if problems go away.

Thanks for the ideas guys.
Mr.P, I will check the dist. pick up. Is there a method you could suggest?
J body, the 6al is mounted on the ds fender near the back close to the fire wall.
It does not get hot to the touch when the problem is occurring.
Second 70, I did try disconnecting the tach. Does not seem to help.

There is a spec for OEM pickup resistance. I can only assume that all aftermarket pickups would follow suit, so that they all work with all ignition systems. I think spec was around 900-1,100 ohms. Pickup air gap should be around .008-.010" if I remember correctly.

You might want to check the ignition rotor for burn-thru...all that resistance in the secondary coil circuit may have encouraged an easier path to ground...seen it before

Had a similar problem a couple years ago: MSD6, Blaster2. One day it just had no fire. Coil was mounted horizontally for years. Box on front surface of rad support, wired per MSD specs, MP electronic dist.
The MSD box tested bad using the MSDD on-car test procedure.
Called the guys at Westech in NC who work on these things for Cup teams, and they were surprised it lasted that long, because mounting oil-filled coils allows them to overheat, which kills the box. They recommended an epoxy-filled coil ('91 F150 302) from any local auto parts store for $31 that's the same output as MSD's $80 coil. I shipped them my box, which they quickly repaired & shipped back by Priority, for about $90.
I had to make a bracket for the coil and also bought a $20 pigtail for a clean installation.
Problem solved, and in fact that motor starts more quickly and runs more cleanly than ever.

Make sure both the power and ground wires from box is going direct to battery, had a issuse with mine not starting and as soon as I wired power right to battery problem went away.