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Can spark-plug-coil-misfire kill the PCM?

5 messages,  Last post on Mar 13, 2009 at 7:02 AM

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#1 of 5 Can spark-plug-coil-misfire kill the PCM? by vic777 Mar 14, 2008 (3:22 am)
Hi everyone,     Please help. I have the 05 Tribute V6 with 59000 mi. on it. It has been running fine and smooth until last week. It refused to start. We towed it to the dealer. After a day, the dealer informed us the PCM was bad and they would replace it under warranty. We were so happy but not for long. The next day, they called us and said all 6 spark-plugs-coils misfired. And that's what killed the PCM. We have to replace them all before they give us the new PCM. The cost is $987 plus tax.     Do you guys think the dealer is correct in their diagnostic? Can spark-plug-coil-misfire kill the PCM? We have the car for 3 and half years. I have never experienced any misfire. The car has alway run very smooth averaging 21mi./gal in mix driving (70% highway, 30% city). Although, I've always thought this Tribute was harder to start than average. I have to turn and hold the key for 2 or 3 seconds to start it. My other cars take 1 second.     Thank you in advance for your opinions.      Vic
#2 of 5 Naive Diagnostics by tveilleux Mar 14, 2008 (5:16 am)
I think your dealer is being very naive about the cause/effect relationship here. The misfire errors are common with older vehicles (the plugs should last for at least 75,000 miles) and usually point to plug/wire replacement of the cylinder that is indicated in the error message. For all 6 to be failing is really pointing to an ignition component that is common to all 6 cylinders.   Were the misfires in the computer error memory before of after the PCM was replaced? If before, then whatever caused that set of messages to be logged in could have caused a PCM failure. However, if the error messages were logged in after the PCM was replaced then the problem could be the new PCM.   Is the dealer certain that the original PCM is faulty, especially in light of the misfire error?   The vehicle computer modules are robust devices and do no break that often.
#3 of 5 Re: Naive Diagnostics by vic777 Mar 15, 2008 (12:49 am)
Thanks for your reply. I don't think the misfire kill the PCM either. But Mazda will not pay for the new PCM unless we change all 6 coils. So, we paid and the car was fixed. They told us the old PCM was dead. They could not read anything out of it. After the new one was put in, they started the car and hooked it up to their diagnostic system. The system showed misfire on all 6 of the coils randomly, intermittently. But the worst and the most consistent is from #2 and #4. They changed out the 6 coils, test drove and hooked it back up to their system. The misfires were gone.   When we get the Tribute back, it starts immediately (1 second) instead of 2 or 3 seconds as always before. And it feel a little stronger and smoother than before.   I think the old PCM has always had a small defect from the start from the factory. It just finally died after 3.5 years. And the misfires were just a common problem with this model. But that is hard to prove.   Again, thank you for your reply. Replies to this message: bhut (May 20, 2008 6:29 pm)
#4 of 5 Re: Naive Diagnostics [vic777] by bhut May 20, 2008 (6:29 pm)
Replying to: vic777 (Mar 15, 2008 12:49 am) My wife and I just picked up her 05 V6 Tribute from the dealer tonight for this exact problem, but luckily it was repaired under warranty (43K miles). We were told a TSB exists on the spark plugs which can cause the coil packs to malfunction, ultimately this led to the PCM dying. At least that's the theory. Our Tribute has always been slower to start in my opinion, pretty much matching your experience prior to the repair. Our truck has never performed well in the mileage department, so I am hoping this improves that end of it. I've been working on vehicles as a shade tree mechanic (for fun no less) for the better part of 20 years, and had never heard of spark plugs causing PCM failure. On the other hand, I spent 8 years working in electronics and saw how sensitive some components can be, particularly to operation outside of their intended range. In my opinion, either the plant got a really bad batch of plugs in 2005, or the coil packs are too sensitive to impedance/load variations. Whatever the case, you may be able to petition Mazda about the coil costs, since a TSB apparently exists for the spark plugs and their potential for damage to the coils.
#5 of 5 Check engine light by beargiel Mar 13, 2009 (7:02 am)
My 2002 Tribute will spit and sputter, not accelerate like it should and check engine light comes on ONLY when it is wet outside. Once it sits in a dry location/weather for a day, it runs fine. Do you know?

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