Anyone know how to test for a blown ignition module?

Hi guys, so I got my new engine fired up about a month ago and have put about 500km of break in on it. And then yesterday I tried starting it to move it out of some bad weather and no joy. I have subsequently checked everything I could think of. Cleaned the spark plugs, checked fuel to the carb, fuel pump operation, checked if there was current between the coil and the distributor and there was plenty.

Then I checked if there was current in the plug wires-nothing. So I opened up the distributor and everything looks fine, including the carbon. It had been raining all week and the car hadn't moved so I was wondering if it was humidity. I used a blow-dryer on the distributor with the cap removed and then put the cap back on and still no spark at the plugs. I'm thinking the ignition module might be blown, but the distributor is brand new! It's a Mallory 4248201 magnetic.

Does anyone know what might be wrong or how to test the module?

Thanks!

Yep, magnetic pickup died. They do that with no warning. Best to carry a spare in the trunk even if you never need it.

wow, does Mallory replace them under warranty? Cuz from what I've seen they're 100$ a piece. I bought the distributor 2 months ago

So to conclude this little saga, it turns out that Mallory and Summit racing have excellent customer support and warranties. They replaced my ignition module free of charge because it was still within the first 90 days after purchasing my distributor. I checked all my wiring as well as the voltage regulator to make sure there was no voltage sparks that could fry the module. Car ran great for 500 kilos and then I went for a drive, and came back home. When I was about to go out again....the car wouldn't start....again..... I got frustrated and went to bed, the next morning I tried it again and it started right up, meaning that the new problem was not with the module.

I then proceeded to chase electrical gremlins for the next two weeks, eventually isolating the problem to either the ballast resistor or the coil. The car would refuse to start whenever hot (no current going to the distributor) and would have no problems when cold. Once started it would run for as long as I wanted without any issues. In the end Summit replaced both my coil and ballast resistor under warranty. I swapped them out today, went for a drive, turned the engine off and back on, and so far everything looks great!

I don't know what could happen to a coil or ballast to cause such a weird on and off problem but at least it seems to be working correctly now.

Aaaaaaaannndddddd..........the electrical problem is back

Car starts fine when cold, runs fine, doesn't start when hot. Module has been changed, coil has been changed, ballast resistor has been changed, wiring has been checked, harness connectors have been checked. No current exiting coil during cranking, spark discharge after key is turned back to off. Any ideas?

David Have you checked your ignition switch? If the ignition side of the switch is getting worn, it could be making intermittent contact.

Holy crap you're right! What would be the best way to test it in your opinion? never had one fail on me. Do I have to take the whole column assembly apart? But how would an ignition switch problem be related to how hot the engine is/how long the car has been running in the previous hours? Also, the on and off/hot-cold problem only started after I changed the module, could I have somehow done something wrong in the module installation that could cause this?

Thank you for your wisdom Hotrod

If you have the GM column with the key on the side, the switch is actually located about halfway down on the top of the tube and operated by a rod from the lock.  My car is pretty tight under the dash, so you might have to drop the column down to get to it.  

I have seen them fail and do strange things.  The contacts may be worn down and heating up due to being smaller and/or not making good contact.  

I would hook a multitester or test light up to the ignition 12V + lead and get someone to work the switch back and forth.  You may be able to see the circuit opening. If you do have to drop the column, I would just replace it. Way to hard to get to if yours is like mine.

I haven't bought one of the switches in a long time, but I don't remember them being very expensive.  If you do replace it, check the replacement against your original.  The tilt columns use a switch that operates in the opposite direction from the non-tilt columns, but looks very close to the other.

Also, check the +12V wire all the way from the switch to the coil.  You may have some bad splices that are heating up or making bad contacts.

Hope some of this helps.

Mike

BTW - Your statement that you got a spark when you moved to the off position is what got me to thinking. If you have a bad contact in the switch, it would probably make an intermittent contact as it was being moved. The ignition circuit might see something like old time points opening and produce a spark. Just my 2 cents.