MSD Ignition box question - inanimate object is getting the better of me.

[CarolinaColtCollector]

So, I consider myself a pretty stupid fella but this is making me feel really stupid. I feel like I need a sounding board or someone to say “yeah mine did that and it was XYZ” so I’ll feel a bit better.


My 84 Grand Wagoneer randomly loses spark when it’s up to temperature and normally when off the throttle or coming to a stop. I know it’s actually losing spark since I’ll hook a test light to the coil and after it sits for a few, it’ll regain it and fire back up, only to stall again a few minutes later.

I went through every connection on it earlier and moved a few wires around to make sure connections were good but she still stalled, albeit after a longer amount of time running (35 minutes or so)

Box is hooked to the battery, pickups are clear of the coil power wires, box should be getting 12v of power when the ignition is in the crank/run position. I’ve done the spark test with a paper clip to confirm what it should look like when working, but I need the bastard to actually cut off when warm so I can do the procedure and check for spark. If I can’t get spark when it’s acting up, I’m going to check for voltage at the ignition trigger wire, and if it has it, I’m going to assume the MSD box is getting hot or something internally and losing the spark signal.

Is there anything else I can check? Or anyone just had a MSD box go bad? I’ve tried a new coil, smacked the box a few times, jiggled wires, the ignition switch, etc. Nothing I have done as of yet has made it cut off unless it wants to.

Ignore the household wire nut, that was a previous owner thing and I’m trying to figure out what it goes to.

 

[Supermatch]

To answer your question, yes, it could be either. Yes, MSD boxes do just go bad. The newer ones much more so than the older ones, to the point where I won't run them in anything I own anymore. I have had multiple 6ALs, a 7AL, a Digital 6, and DOA 7531 boxes, along with several failed coils as well. One other test you can do is to check resistance across the magnetic pickup when warm. They have a tendency to fail open or with high resistance, I don't recall what the test value threshold is offhand though.

 

[CarolinaColtCollector]

To answer your question, yes, it could be either. Yes, MSD boxes do just go bad. The newer ones much more so than the older ones, to the point where I won't run them in anything I own anymore. I have had multiple 6ALs, a 7AL, a Digital 6, and DOA 7531 boxes, along with several failed coils as well. One other test you can do is to check resistance across the magnetic pickup when warm. They have a tendency to fail open or with high resistance, I don't recall what the test value threshold is offhand though.

I had actually changed the ignition pickup out with a new part wondering if that was the issue, that turned into a 3+ afternoon debacle trying to figure out what happened. It wouldn’t take fuel without backfiring out of the carb, and wouldn’t rev with the vacuum advance hooked up. Finally got that fixed and was welcomed back with the stalling issue.

Also managed to run the side of it down my engine stand trying to get it back in its parking spot, so that’s fun.

 

[Pogue]

In my experience, msd boxes don’t need a reason to fail. They just do. Is there any specific reason you run one on what appears to be a stock engine? Not trying to be rude, but I’ve been stranded in the side of the road asking myself the same question before.

 

[CarolinaColtCollector]

In my experience, msd boxes don’t need a reason to fail. They just do. Is there any specific reason you run one on what appears to be a stock engine? Not trying to be rude, but I’ve been stranded in the side of the road asking myself the same question before.

Not rude at all.

2 reasons I guess, it was that way when I got it with the engine that originally came in it, and it’s far from stock 😉

 

[Pogue]

Not rude at all.

2 reasons I guess, it was that way when I got it with the engine that originally came in it, and it’s far from stock 😉

Gotcha!! What secrets is that thing hiding?!

Try taking the box out of the equation and seeing if the problem persists. If not and you’re not blowing out your spark there’s no reason to replace it.

 

[CarolinaColtCollector]

Gotcha!! What secrets is that thing hiding?!

Try taking the box out of the equation and seeing if the problem persists. If not and you’re not blowing out your spark there’s no reason to replace it.

It’s a built/blueprinted 401 and 800cfm Edelbrock hiding under that air filter. It’s not the biggest engine out there, but it’s the biggest one that Jeep made and has about 170hp over factory.

How do you maintain spark while taking the box out of the equation?

 

[Pogue]

It’s a built/blueprinted 401 and 800cfm Edelbrock hiding under that air filter. It’s not the biggest engine out there, but it’s the biggest one that Jeep made and has about 170hp over factory.

How do you maintain spark while taking the box out of the equation?

I bet it’s enough to get that wagoneer moving!

Simple enough to bypass the box. Just reconnect the coil directly to the pickup in the distributor as it was from the factory.

 

[CarolinaColtCollector]

Box is bad, hunt begins for one!

 

[Supermatch]

May want to consider an HEI conversion in lieu of an MSD box. The MSD box won't gain you anything outside of more headaches.

 

[CarolinaColtCollector]

May want to consider an HEI conversion in lieu of an MSD box. The MSD box won't gain you anything outside of more headaches.

Here’s the part where y’all are gonna judge me. I have a brand new DUI distributor for AMC engines sitting with all my Jeep stuff, I was planning on using it for another project, but might just have to order a second one.

 

[Supermatch]

Here’s the part where y’all are gonna judge me. I have a brand new DUI distributor for AMC engines sitting with all my Jeep stuff, I was planning on using it for another project, but might just have to order a second one.

Do it. There's a lot to be said for being able to slap over the counter GM distributor parts in there to get moving again...