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Spark?

Hogback Fabrication

Hogback Fabrication

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Well, my truck's intermittently dropping spark again. Here's the story:

~6 months ago my truck randomly dropped spark to all cylinders. At one point, the truck wouldn't start so I was able to try and diagnose the problem. The distributor was getting 12V but wasn't throwing any spark. I figured the problem must be either the coil or ignition module. I replaced the coil with a known working one and the problem persisted, so I replaced the ignition module.

This fixed the problem until yesterday. The distributor is an MSD pro-billet HEI and is only a few years old. It really acts like the ignition module is bad again. I am going to send the module into MSD and see what they say, at least this one will be under warranty.

My question is this: Is there any way my truck is killing ignition modules? Or does MSD just suck at making them? My voltmeter hasn't been saying anything unusual.
 
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Modules are fairly prone to failure (at least stock ones that are still original lol) but the only other module killer is typically heat from not using the supplied grease. If MSD made your complete distributor, I'd think that not to be a problem.

Have you talked to MSD about the issue? Have you tested the module yourself to see if it IS bad? If it won't start at all now, that would be a good place to start. Obviously with electrical stuff, just because it test good when cold doesn't mean adding heat or vibration to the equation won't change things. :) This is why the parts store tests are marginally effective, at best.
 
The supplied grease (or thermalpaste type stuff) was on there stock and I cleaned up the mounting surface and reinstalled the grease when I replaced the module.

The truck runs perfect right now, it only drops spark sometimes. As I said before, the only way I could trace it to the module before is I had to wait until the truck wouldn't start. So as of right now, since the truck runs fine, I don't think I can check the module.
 
Does it actually die when it acts up, or are you just dealing with something that acts like a random misfire?

Since it's still random, I'd be checking the connections in the ignition system. From the fuse panel feed to the pick-up coil leads.

Any wires you can move while it's running can be checked as well.
 
The truck will randomly drop spark to all cylinders just for a second or two. You can watch the tach fall to 0, then jump back up when spark returns. It just started acting up on Saturday and I haven't had a chance to mess with it.

Again, I'm reasonably certain that the problem I had before was the ignition module. It really feels like the same thing. If it is, I was hoping someone could help me keep this from happening again. :dunno:
 
Had a similar problem once after rebuilding a motor and new distributor. The wire and/or where I was getting the power from wasn't able to carry enough current. The truck would run fine when I first started it up but after a while when the engine got warm the module would overheat and cause the thing to not idle and have no power. I ran a 10 ga. wire from the battery to a relay and 10 ga. from the relay to the distributor and no problems since. Just my .02:D
 
When I had a similar problem it was from the Tach wire grounding out where it went through the firewall. Unhook the tach wire and see what happens maybe?
 
Tominator II said:
When I had a similar problem it was from the Tach wire grounding out where it went through the firewall. Unhook the tach wire and see what happens maybe?
Click to expand...

I thought of the same thing the first time I had this problem. Didn't fix it. I would bet a lot of $$$ that the ignition module was bad the first time.
 
90v1500 said:
Had a similar problem once after rebuilding a motor and new distributor. The wire and/or where I was getting the power from wasn't able to carry enough current. The truck would run fine when I first started it up but after a while when the engine got warm the module would overheat and cause the thing to not idle and have no power. I ran a 10 ga. wire from the battery to a relay and 10 ga. from the relay to the distributor and no problems since. Just my .02:D
Click to expand...

The truck ran perfectly for the first 12,000 miles or so on this ignition setup. I doubt anything was wrong from the beginning.
 
I had the same problem in my old Toyota it was a bad ground strap from the motor to the firewall I put a new one one and problem was solved.
 
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