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Dave Moore

PCM replacement

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Returning to slip after idling in for approx. 10 min.  Eng. died. 454 Merc Mag.  2004  Called tech and had him come out today. Hooked up computer but would not interface with PCM  He thinks need new PCM.  Even if PCM was bad wouldn't he still get a reading?

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The 496 uses the PCM-555 and it uses a unique patch cable. I'd have another tech attempt a scan with a different scan tool before I'd spring for a new ECM as a failure there is very rare. To access the data stream, the helm station feed gets unplugged at the ECM branch connector and the scan tool gets plugged in there. Always a possibility that there is an issue with that short cable also. If the ECM has failed, the next question is why. Not good to plug in a new ECM and fry it because a IAC has gone to ground or something similar. W

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