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318 V8 ignition coil - major problem


Old 06-29-2011, 02:28 PM
FDSJr is offline
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Default 318 V8 ignition coil - major problem

I have a 1993 B250 Ram Van with a 318 V8. The PCM was acting up (no signal to #5 injector), so the dealer replaced it with a new PCM. This was on June 17 and all seemed to be fine.
Then, on June 22, the OEM ignition coil failed. This was after 1 1/2 hours of driving since the new PCM was installed.
The dealer installed an aftermarket ignition coil to replace the failed one.
On June 27 the new coil failed.
Since I was on vacation and about 200 miles from home, I had it towed to a different dealer. That dealer installed an identical aftermarket coil.
After about 2 hours of driving, that coil also failed.
The vehicle was then towed back to the original dealer. They installed an OEM coil this time, but I have no confidence that it will last very long until it is also killed.
I have had 4 ignition coils fail in the 10 days since the PCM was replaced.
The dealer claims it can't possibly be the PCM that is causing it. I tend to disagree since the replacement of the PCM was the only thing that was done before this all started to happen.
Does anyone have any thoughts on this mystery?
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Old 06-29-2011, 07:21 PM
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Welcome to DF. First, before anything else, please read this.

I will move this to the Ram Van section for you.
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Old 06-30-2011, 12:09 AM
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The PCM regulates alternator power. If the new PCM isn't doing so, there could be too much power going into the ignition coil and burning it up. The first step would be to take volt reads at the coil's primary wires both at idle and at 1500-2000 RPMs.
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Old 06-30-2011, 01:31 AM
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And to replace the ignition coil, it only takes a few turns on the wrench and pop off the wire. Having a dealer do this is costly. The coil is in an easy place to get at too.

Alloro is correct, the PCM does control the alternator voltage. Go back to the first dealer, take with wisdom and get the PCM replaced with one that works. Also see if they will ocver the coils that burned up too.
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Old 06-30-2011, 01:22 PM
FDSJr is offline
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Thanks to Alloro and Stev. The service tech at the second dealer was very helpful. He took me into the shop and showed me exactly where the coil was located, how to get at it, and how to replace it. I am not sure that his bosses would appreciate him passing on that money saving tip....but, I appreciated it.
The coils (after the first failure) have been replaced at no cost to me, other than the aggravation of having to wait to be towed to the dealer and wait for the repair to be completed (but, towing costs were paid in full by AAA).
I will check the voltage at the primary leads of the coil and see if that tells me anything.
Thanks again to both of you.
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Old 07-04-2011, 03:16 PM
FDSJr is offline
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I have a little more information and want to see if anyone has additional insight.
The dealer is still reluctant to to look at the PCM as the culprit since the latest coil hasn't failed (yet). I also haven't driven the van much since the latest coil replacement, but I am sure that it will eventually fail.
During this latest coil replacement, the dealer said that they found the resistance on the battery negative cable to be a little high and claimed that this could be the cause. Maybe I am missing something here, but it would seem that a high resistance would reduce the voltage and power rather than increase it and cause the coil to burn up.
I have not been able to check the voltage at the coil primary leads, yet, but I did check the alternator voltage at the battery. It is no higher than 14.28 volts, even at very high rpm.
When I am able to check the coil primary voltage, what value should I expect to see if things are operating normally?
Thanks again for any help that you can give.
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