Electronic ignition woes what am I missing??

[70RT4SPD]

This will seem to be a bit lengthy and yes it’s on a truck but it’s the same ignition setup as my coronet also I’ll try not to ramble on…

75 D350 dodge dump truck. 318 2bbl with a getrag 4 speed. Cab was rotten so it’s been changed to an 87 D250 cab and front clip. The truck has sat for many years but when it ran it ran great. The problem is I have no spark until you turn the key to off and it gives it a “poof” fire or momentary spark on key off not released from key start to run. Replaced the balast, no luck. Bypassed the balast with a jumper wire, no luck. Replaced the ECU (well grounded) no luck. Replaced the pickup coil… no luck. Checked the bulkhead for anything fried all looks good. Also replaced the coil, the starter relay and the ignition switch in the column and you guessed it still same problem. I noticed I was only getting about 9.5 to 10 volts to the positive coil when cranking which isn’t enough to fire it. At this point I’m at a loss and I don’t want to keep firing the parts cannon at it. I’m thinking I’m missing something obvious but can’t figure out what. The 87 cab was an automatic that had a 360 4bbl with a dual pickup coil so there is extra wiring that’s not hooked up. I tried an extra electronic ignition harness that I had from a parts lot to attempt to seperate the ignition system from the truck that was powered by a direct 12v battery operated switch to see if it would make a difference and it didn’t. At this point I have all extra testing wiring and switches removed and hooked back up from the 87 truck harness. Any input as far as testing procedure would be helpful as I keep spinning my wheels on this one. Thanks!

 

[Beechwood45789]

I had a different but similar problem where the car would run if I held it in the start position but would die when I let off. Checked and changed everything that you did. See what your voltage is doing at the turn signal switch connector. Run and start are two different paths, I had voltage in start but nothing in run. I cleaned the connector and it fixed it.

 

[WileERobby]

You get a schematic, and you trace the entire ignition primary circuit with your multimeter.

 

[Kern Dog]

I have this exact same condition in my 75 Power Wagon. It is intermittent though.
Most of the time, it fires when it should. Other times, it cranks and cranks but won't start, then as I release the key from the spring loaded "start" position, it tries to start. Wiggling the wires to the ballast resistor usually gets it to start correctly but not always. I don't drive this truck that often so it hasn't motivated me enough to fully solve the issue. I did have this same thing happen on other Mopars with the factory electronic ignition. My '70 Charger used to have an occasional no-spark condition that mostly happened here at home when I first wanted to start it to go somewhere. It only failed twice out on the road. The last time I changed the coil, ballast and ECM before it fired up. The time before it, simply replacing the coil was enough. In fact, I almost though the damn thing was voodoo or possessed because it seemed to defy common sense and only start when IT wanted to. In reality, it probably was a matter of a dirty or loose connection somewhere.

 

[Geoff 2]

10V to the coil while cranking would be normal. I would look elsewhere.

 

[451Mopar]

I had that problem, bad battery cables.
Also, check the reluctor to pickup gap.

 

[Demonic]

Get some alligator clips for your voltmeter, so you can see voltage from the key at various points. I'd start testing the ignition switch - repeatedly.

 

[HALIFAXHOPS]

You need to troubleshoot the "start" circuit. It is probably something simple like a dirty connection. Remember a voltmeter is great but if the connection is dirty, it will pass the voltage and not the amperage. Load light is your friend here.

 

[blue69runner]

Is the motor ground good. Sometimes you find that you do not have a good ground. Found this in many applications. Lawn mower-Tractor and other motor driven applications. Wish you luck. Know it will drive you crazy!!!!!!!

 

[dvw]

The ignition switch has 2 feeds. One feeds in ignition on. Usually a blue wire. It feeds to the ignition key side of the ballast. It goes dead during crank. The second feed is hot in crank only. Dead in run. It is usally brown and bypasses the ballast to the coil +. It can be attached to the coil side of the ballast. They both feed to the coil + cicuit. This way you will have + voltage in crank and run at the coil. My bet is you are missing the + crank feed.
Doug

 

[Dragon Slayer]

I agree 10V plenty at coil. The ECU will fire once when you stop cranking. Had this once when someone redid the connector on the harness to distributor and it was reversed, so the ECU was seeing a different pulse.

If you had another car, you can move the ECU to it and see if it works. Same with coil. I would also look at the strength of the spark at the plug wire. If not strong, I have seen ECU fail that will spark, but just real weak.

 

[Master Gunner]

There should be a wire running from the starter relay terminal marked BAL to the brown wire (coil feed) at the ballast resistor. This is to provide more power for easier starting, then going back to 8V in the run position. If the wire isn't there just make a jumper to serve the same purpose.

Mark

 

[70RT4SPD]

Thanks everyone for all the feedback I will definitely be poking around at it this weekend if the weather holds up!