I have a 2002 Ram Van 1500 with the 3.9 V-6. Twice now in the last month or so the coil has failed, leaving me stranded. The coils tested out with 10-11k resistance, but would not run the van. Replacing the coil, it fired right up. Anyone have any ideas what is going on here? I've had an intermittent CEL for misfires, but have not been able to track anything down. I replaced the wires and plugs, and isolated the wires extremely well so they can't crossfire or short. I'm open to any other suggestions.

 

It may be the 12V plug that supplies power to the coil. Try cleaning the connector and also apply some silicone grease before reassembling.

 

How would this be making the coil fail? I can't see any issues with the wiring.

 

Well, if there is no 12V power source to the coil it fails.



Seriously though, when you changed coils you moved the power supply plug around, possibly into a position where it was making good contact, therefore making the coil work.

If the coil tests out on the bench it should work in the vehicle. Only variable would seem to be the power connector.

 

Have you previously upgraded to 8mm or larger performance ignition wires? How about performance spark plugs? If one or both have been done, the extra energy load will take out a coil gradually until it totally fails. Have you had issues of hard and long starting?

 

There is nothing wrong with the power plug that is obvious, it fits tight. The plug wires are stock type, 7mm I think, though I'm not sure what that would have to do with it. Performance wires usually have less resistance, not more. The van ran for 100,000 miles before it started having this issue, so I tend to think it's the coils themselves, but it's odd that two would fail quickly when they are a quality brand not known for issues, and not purchased at the same place. I've never heard of certain wires or plugs making a coil fail. The van has always started instantly.

 

I think my '94 van's problem is very similar to yours.

Using an oscilloscope to monitor the coil's lowside driver and other signals at the PCM, I have discovered that 12 Volts is present at the PCM side of the coil primary when the engine dies and also when it won't restart. That means:
(1) the coil's primary winding is connected to the 12 Volts that's supplied by the ASD relay contact and
(2) the coil's primary winding is not open-circuited.

Also, the PCM is activating the fuel injectors but not the coil when the engine won't restart. Given all the above, I believe my van's problem is a failure in the coil driver circuit; i.e., there should be no combinations of inputs to the PCM that would result in the PCM purposely driving the injectors but not driving the coil.

I believe the culprit is either an intermittent connection (or wire crimp) at the PCM pin or it's an intermittent inside the PCM itself.

Tonight, I disconnected the PCM connector. I visually inspected the pins but didn't see any problems such as bent or corroded pins. I did see some white material on the pins, which I believe is silicone grease.

I'll go back and do some continuity tests between the wire harness pin (pin 19 on the large connector that mates with the PCM jack) and the wire leading to the coil. I'll do the same with the power and signal ground pins.

If those pins test good, the PCM is the only thing left to repair or replace.

Did you resolve your van's problem?

Thanks,

Jeff

 

The van quit on me again and I had it diagnosed at a Dodge dealer, they said it was a defective PCM, not driving the coil. I replaced the PCM and it worked, but still has codes for misfires. I've never been able to solve that problem.

 

I wonder how your PCM detects a misfire. Maybe it senses dc current during the time when the coil is grounded by the PCM's coil driver. Can you tell if your van is actually misfiring (running rough)? Also, with later model PCM's (~98 and on), I read that the dealer has to program (or flash) the PCM. Did the dealer program the PCM based on your van's VIN?

I see your van is a lot newer. Not sure my 94 van's PCM has codes for misfires.

Concerning my van...........

I've checked 4 key pins at the connector that mates with the PCM: the coil driver, 2 power grounds, and 1 signal ground. I disconnected the mating connector at the PCM. I then used an insulation-piercing probe to connect to each wire and tested continuity from that point to each applicable socket on the mating connector. I tugged the wire-under-test while checking continuity, looking for a possible bad crimp in the factory wiring harness pin. All 4 pins were rock solid. I also checked continuity between the grounds and the van chassis and the negative battery post; all were good. While I had the connector off, I did a visual on the PCM's pins; all looked good, just a little silicone grease there.

Last night, I removed the coil. I connected the DMM and measured continuity of primary and secondary windings while I heated the coil with a hairdryer. Also, I rapped it a few times with a small hammer. Continuity readings were in-spec and solid, varying only slightly due to the temperature rise from the hairdryer.

Therefore, I think my next move is to repair or replace the PCM. I doubt that the PCM is repairable but I'll take it off and try to open it anyway. Looking at the oscilloscope waveforms I've collected over the last 2 months, it's possible I'll be able to find the intermittent connection in the PCM's coil driver circuit. Also, I can hope that the final stage of the coil driver is a common component that I could replace if I feel that's the problem (e.g., an intermittent at the internal connections to the silicon in the power transistor).

I'll post results when I have the solution.

Thanks,

Jeff

 

There's a notch on the flywheel corresponding to each cylinder. As each of these notches pass the crank sensor it sends a signal to the PCM which triggers the coil. If the PCM detects more than 40 thousands of a second difference between two notch triggers it is counted as a misfire.