[Power Hungry]

So here's the problem....

On the early EEC-V 88K and 112K PCMs, we've experienced what is called "timing drift". This is when the clock circuit (the crystal and related capacitors) age and the generated clock frequency starts to drift.

Since all the internal circuits run from the same clock signal, this does not have any effect on the operation of the PCM and the vehicle will start and run just fine. However, timing drift also controls the communications BAUD rate, as this is directly related to the clock signal.

The scan tool functions on its own clock signal to generate a BAUD rate that is comparable to the one that is SUPPOSED to be generated but the PCM. If the PCM is running a tad slow then the BAUD rate between the two devices won't match. In minor cases of timing drift, the communications can still function correctly. However, if the BAUD rate is off by more than 1.5%, the scan tool or other external device will not be able to reliably communicate with the PCM.

This communications issue is something I've seen as far back as 2004 and seems to be unique to the DPC-2xx and DPC-3x (88K and 112K, respectively) PCMs. To date, I've not experienced this with any of the DPC-4xx (216K) PCMs.

One thing you can try is to thoroughly clean the grease and silicone coating from the J3 connector. You can also use a brass brush to clean the silicone from around the Flash ROM. I can't explain it, but I've found that this has actually helped clear up the communications issues. All I can assume is that the coating created some sort of draw that slows down the clock. I've done this on the bench with PCMs that would otherwise not communicate and they suddenly worked afterwards.

If all else fails... Put a chip in it. That'll at least get you a good tune on the PCM.

Let me know if any of this helps.