Help! Strange ignition problem continues 1971 440 4 speed

[mbc0724]

Next time you go for a drive, take an old spark plug with you. When the problem occurs, remove a plug lead & hook up the lead to the old plug & lay it on the engine. Crank to see if get spark...

Thanks--did that and no spark. Fortunately, the problem occurs when the car comes back and is in the driveway!

 

[Ron H]

Check all electrical connections and harness(s). Yes ok, seems obvious, but don’t make assumptions; check if they’re TIGHT and look closely at the contact area for possible indication of heat damage. This may not be the hassle, but I toss it out having had a problem with a poor connection inside a new harness…it caused overheating and loose connection with a wire in the harness. Didn’t notice it until seeing the damage and gently pushing in the harness wire finding it loose.

 

[WileE]

Again.... he already said, he's got fuel. Again... he already said, no spark at the coil. So... see post #13. Is the coil getting voltage ? >you trace the ignition primary circuit. See posts #17 and #22, as Ron says it could be that simple.

 

[mbc0724]

Again.... he already said, he's got fuel. Again... he already said, no spark at the coil. So... see post #13. Is the coil getting voltage ? >you trace the ignition primary circuit. See posts #17 and #22, as Ron says it could be that simple.

Thanks guys--I'm not real good at this electrical tracing stuff. I need to figure out how to trace the ignition primary circuit. It all makes sense.

 

[WileE]

The FSM has a schematic. The primary circuit is the low voltage circuit up to the coil. It the two small wires connected to the coil. The coil "transforms" magnetically the low voltage to high voltage which is what comes out of the coil into the spark plug cables, the secondary ignition circuit. Since you say there's no spark, first question is, does the coil get voltage at the time of the symptom ? A simple multimeter will help you along the circuit.

 

[RJRENTON]

magnetic pick up in the distributor - a most common failure but overlooked by the rocket scientists on all the forums

connect an ohm meter to the 2 terminals and spin the distributor. The ohm meter will change state from a reading in ohms to open circuit as the reluctor passes the pick up.

The ohm meter reading will read resistance of the pick up coil. When in operation, "spinning" of the distributor will result in a average voltage generated by the reluctor and the pick up coil...that triggers the ECU, to produce the spark......and as you noted, ohm meters will provide a false readings due to the meter's circuitry......not indicative of a faulty pick up coil......1000 rocket scientist's can't be wrong......most likely it's the coil or ECU that is/has failed.......just my opinion.....
BOB RENTON

 

[mbc0724]

The ohm meter reading will read resistance of the pick up coil. When in operation, "spinning" of the distributor will result in a average voltage generated by the reluctor and the pick up coil...that triggers the ECU, to produce the spark......and as you noted, ohm meters will provide a false readings due to the meter's circuitry......not indicative of a faulty pick up coil......1000 rocket scientist's can't be wrong......most likely it's the coil or ECU that is/has failed.......just my opinion.....
BOB RENTON

Thank you Bob. I replaced both and no change. But it's possible the new coil isn't good...I will be checking.

 

[mbc0724]

The FSM has a schematic. The primary circuit is the low voltage circuit up to the coil. It the two small wires connected to the coil. The coil "transforms" magnetically the low voltage to high voltage which is what comes out of the coil into the spark plug cables, the secondary ignition circuit. Since you say there's no spark, first question is, does the coil get voltage at the time of the symptom ? A simple multimeter will help you along the circuit.

Great advice--will try to get to it in the next day or two. Pesky job is getting in the way!

 

[mbc0724]

Check all electrical connections and harness(s). Yes ok, seems obvious, but don’t make assumptions; check if they’re TIGHT and look closely at the contact area for possible indication of heat damage. This may not be the hassle, but I toss it out having had a problem with a poor connection inside a new harness…it caused overheating and loose connection with a wire in the harness. Didn’t notice it until seeing the damage and gently pushing in the harness wire finding it loose.

Thanks!

 

[mbc0724]

magnetic pick up in the distributor - a most common failure but overlooked by the rocket scientists on all the forums

connect an ohm meter to the 2 terminals and spin the distributor. The ohm meter will change state from a reading in ohms to open circuit as the reluctor passes the pick up.

On my list--thank you

 

[69-73RR]

Thanks for all of the comments since my last post a week or two ago. But the problem persists. Quick recap: Car starts cold perfectly, runs very well, idles fine, drives without any issues whatsoever. Get to destination and turn off the car; wait 10 minutes; the car will not start again. It just cranks and cranks and cranks. However, wait a few hours, and the car starts right up and drives fine again. No issues. Repeat like clockwork--will not start after driving it around until it is fully cold again.

I have changed the ECU, coil, cap & rotor and ballast resistor. Have searched for bad wires and found nothing. No change in the pattern. I have been assuming this is a spark or electrical issue. But have not ruled out fuel. Yet the car runs and starts from cold so perfectly, and runs so well afterwards, that I cannot see a fuel issue. It seems to be heat-related, since the problem only occurs with a hot motor. But who knows.

Any suggestions to finding the gremlin responsible for this strange problem?

Thanks!

Had the same problem on my 69 RR 440 MSD ignition. Eventually wouldn't start at all. Turned out to be ground wire from MSD box at
negative terminal. It was completely corroded under MSD ground wire connection and was not visible because of connector cover. Found by accident when I cut terminal at cover. It was completely covered white inside. I went through a lot of pain and cost with this problem.

 

[Marks69Bee]

Next time you go for a drive, take an old spark plug with you. When the problem occurs, remove a plug lead & hook up the lead to the old plug & lay it on the engine. Crank to see if get spark...

Thats a good idea Geoff.

 

[Darryl Tilton]

Had the same problem a couple of years ago. Checked for spark and had none. Replaced the relatively new orange Mopar ECU with a spare black Standard box, no problems since. Now I carry a spare ECU with my extra ballast resistor in the glove box in both Mopars.