PCM hardware questions regarding reflash

[cleatus12r]

Are the REALLY old EEC-V 7.3L processors unable to be reflashed?

The reason I ask is because I have in the shop a 6/94 build Powerstroke with a BEG8 PCM. I have no communication on the 16-pin connector under the dash (powers a scan tool fine) and therefore cannot flash through the DLC. I also have an off-board adapter and it works just fine on other DPC-203 PCMs around here but will not do anything with this very early-bird. It will not "wake up". The vehicle runs fine other than being here for a set of injectors but I can't do any diagnostic routines or get live data. I was hoping to flash it to a VDAB0_02 but I can't even do it on a bench. Replacing the stock PCM with another DPC-203 proves that the DLC wiring and diagnostic systems are functional.

Do I have a faulty PCM here or a PCM with different hardware that will not work with my flash tool? I can read it through the J3 port all day and "chip it" but anything "front door" is no bueno and I don't want to waste a chip (or charge for one) just to put a later stock calibration on it that would allow for a datastream.

[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.

[cleatus12r]

WOW! Thank you, Bill! That anomaly escaped me completely.

Here's another weird thing about it....which may be related to the internal clock thing: The idle is fast. It has a warm idle of around 800 give or take based on the tachometer (since no data) but when a functionally good PCM is in it, it's normal. When a minute isn't quite a minute, this would make sense.

The guy isn't worried about it as it's a worn-out ranch pickup. I just wanted to do some computer-based diagnostics on it even though it was an obvious injector issue once all mechanical possibilities were ruled out.