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Discussion Starter · #1 · (Edited)
Engine 2006 GTP 3800SC series III engine. Problem: Misfire and DTC P0300 that appeared suddenly while driving. The code is random misfire and could be the result of a defective coilpack, ignition module, crank position sensor, injector or vacuum leak. I suspected an erratic spark problem as the exhaust smelled rich
After testing the spark with a timing light on each plug wire, we were not getting a steady spark output from the 2 and 5 center coil pack. The coil tested good so I assumed it was most likely the ignition module. I removed all the coils and ignition module. I noticed a bit of corrosion on the bottom of the ignition module and on the plate that it attaches to. On a whim I sanded the ignition module bottom and the mounting plate clean with fine emery cloth paper. Then applied a film of Conductive heat sink grease. Put it all back together and started the engine. The miss was completely gone, the code went away and a test drive showed really excellent performance. Total labor was under 60 minutes.
Conclusion: The coil pack gets its ground from its surface mount (bottom) to the mounting plate. If moisture gets in there corrosion can develop and it did. Corrosion is an insulator and it prevented the module from making good contact. This is not always a solution for finding the cause of the dreaded P0300 random misfire code but it did work on this repair. We have all the parts needed for a repair but in this case none were needed.
 
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