Mopar Action On-line – Tech Questions


Tech Question

David Buchanan, Hillsobor, OR, 1968 Dodge A108 318

Thanks for all the help you provide to your readers. You are an awesomeresource. I have a problem with my 1968 Dodge van. It has a 318, Auto withelectronic ignition. I rebuilt the engine and transmission a couple of yearsago and it’s run fine with no problems. A couple of weeks ago I drove it tothe store and when I returned from shopping about a half hour later, itwould not start. I’ve never had this kind of problem. I didn’t have thatmany tools and did a rudimentary check for spark by holding the coil wireaway from ground to check spark. Nothing. Popped the cap and the rotor isturning. I got a ride back to my shop and pulled an old module, ballastresistor, coil and coil wire and drove back over to my van. Each of theparts had worked in the past and were replaced when I would upgrade my otherMopars (MSD, MOPAR performance.) I usually don’t try and just throw parts ata project, but it was cold, rainy and I didn’t want to leave the rigovernight. I replaced the coil plug wire, no go. Switched out the coil, nogo. Swapped out the module still no go. Odd thing was that when I crank it,there is nothing, but when I release the key from the start to run positionbefore going to off, it almost sounds like it’s going to start. Just a splitsecond. I know there is always the dreaded bulk head disconnect, but thisdoesn’t have one that I’m aware of. The fuse block is a little rusty but myvolt meter doesn’t indicate an open circuit. Any recommendations? I did getthe van towed back to my shop but I’m kind of baffled.

Thanks again for your great tech and restoration articles. – David


I will assume you have converted to stock-style ’72-up Mopar electronicignition, and that you have a 4-pin ECU.

I don’t have an A-100 FSM handy as I write this, but, obviously, the wiresneed to go through the firewall somehow, so I’d look there first — once youfind and inspect the connector, and problem is usually obvious.

Then you’ll need to do some real, actual troubleshooting, although it soundslike you wanna keep just throwing parts at it, so I’ll mention that youhaven’t swapped the ignition switch and the pickup coil. The easy way to trythe pickup coil is to simply hang another distributor nearby, plug in itsconnector, turn on the ignition, and twirl the second dist’s shaft whilechecking for spark as you describe.

The first step in troubleshooting is to use a DMM and measure the voltage onthe coil’s positive lug. With the key in the run position, it should be inthe vicinity of 8 to 9 volts, and, during cranking, a bit higher. If itfails the first test, suspect the ballast and / or the “ign run” wiring /switch, if NG during cranking, the “ign start” wiring / switch.

It is also conceivable, but unusual, that your (original) coil is shorted,toasting both ECUs, assuming that you tried the ECU first.

Also, be aware that the ECU needs a good ground to function.

There’s a whole procedure to troubleshoot this “by the book”, but usuallythe above will get you going.



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