16197427 PCM woes......

[billygoat]

The wire bundle moved over and laid on top of the EGR base and became 1 big cooked together mess - yes my error for not running them/securing them correctly.

So I set up my bench test, powers/grounds ALDL connector and a CEL, and my 2 units, plus my 2 replacements that showed up all tested out ok???? - truck heal theyself???

So I put a new unit in the truck and turned on the key - code reader showed map error, understandable with it unplugged, old unit, same thing...plug in the map, same thing, ok switch out the map, no error.
So WTH, with the old unit I put the fuel pump fuse back in (I always pull it when I am going to cycle the key on/off a bunch) and fired the truck up - cel on solid, no connection with tool.
So after a few tries, I figured out, no fuel pump fuse, all was ok, with the fuse my old unit would become unreadable, a new unit was fine, so I grabbed my motes adapter (the unit I was using has a socket soldered in the MCAL) and put a new MCAL in an old PCM, and presto - truck started up, no CEL, and data was flowing.

Time for a little happy dance...

So I guess I fried 2 MCALS (something JeepandGuns suggested on the other forum) and the MAP sensor.
What I don't get is what did the bench test do.. the flickering CEL situation is gone, no load and the PCM and all is good, ask it to do something and the MCAL goes bye bye, but limp home mode still works, and yes I was using the same chips I had in during the melt down - however I probably will carry another one on a test drive JIC.

[dave w]

The bench test was to figure out what was working and what was not working. The logic behind troubleshooting, figure out what is good, and suspect anything that can not proven good. Troubleshooting requires doing stuff, trying stuff, often doing stuff that seems unconventional. The WTH moment is often the "I figured it out" moment.

Good Job!

dave w

[billygoat]

By "what did the bench test do" I mean, why did I have a flickering CEL in the truck, but after the bench test, that was gone, it was either on or off... although it does not sound like electronics, could it have been on the edge of working, and some kind of internal protect was kicking in, and on the bench with no load it let it die the rest of the way???

[JeepsAndGuns]

the unit I was using has a socket soldered in the MCAL

So with the memcal that has a socket sodered in place of the stock prom doesnt work, but a stock un modded memcal works? I would inspect the soder joints on the socket.

[EagleMark]

By "what did the bench test do" I mean, why did I have a flickering CEL in the truck, but after the bench test, that was gone, it was either on or off... although it does not sound like electronics, could it have been on the edge of working, and some kind of internal protect was kicking in, and on the bench with no load it let it die the rest of the way???

To test PCM. But should have tested memcal too.

You found the issue in last post. Everyone was pointing to a prom error with the flickering CEL. Then you...
"(the unit I was using has a socket soldered in the MCAL) and put a new MCAL in an old PCM, and presto - truck started up, no CEL, and data was flowing."
So is it the memcal change or something loose? Was the old PCM tested good?

[1project2many]

And there's a very good chance that this problem isn't related to the MAP wiring issue at all. There's very little chance that faulty MAP wiring can burn up a memcal so the ecm has a problem when the fuel pump fuse is installed. It's kind of like saying "The tire blew then I noticed the headlight was out but the light turns on whenever I switch on high beam so how did the tire mess up the lights??"

[billygoat]

I did more comparison testing last night.
Both Memcals in the 2 proms I had connected with the fried wiring will not work when the system has to "do something" no matter which PCM I put them in.
If I leave the pump fuse out it is ok, but unplug another sensor so it should kick up an error, and I lose everything.
I can even leave the pump fuse out and unplug the pump relay, that will kick up an error on a good memcal, but on either frier I get the lost in space result.
I also tried both new memcals in both old pcm both with the moates adapter and without, and everything seemed ok - keep in mind these are just key on test both with everything ok, and with something unplugged to kick up an error.
Actually driving the truck may show something different, I figure that is more a daylight activity.

The only thing nagging at me is the fact that I don't get the flickering CEL, even with no communications the CEL is on solid.
I had swapped MEMCALs on the 2 bad units the night before the bench test, and was getting the flicker on both in any combo, and now I don't, the only thing that changed was the bench test.

[1project2many]

Troubleshooting electronics and computers requires some very exact descriptions. 10,000 lines of programming can be made into garbage by one extra letter.



This assembly is a memcal. The arrow is pointing to the sticker on the EPROM. Often the eprom is removed and a socket is installed in its place like this:



Once the socket is installed you can plug in a programmed eprom or an eprom emulator.

Both Memcals in the 2 proms

Are you trying to say you tried two different eproms in a socketed memcal?

I also tried both new memcals in both old pcm both with the moates adapter and without, and everything seemed ok - keep in mind these are just key on test both with everything ok, and with something unplugged to kick up an error.

Is this the adapter?

If there is no eprom (also known as "chip") plugged into the socket on the left or if the eprom that's plugged in is blank or not programmed properly or plugged in backwards then the ecm will turn the check engine light on and keep it on steady with the key on.

[billygoat]

Passed the road test, even the memcal that that I put in after the melt down came back??
But when I was testing I think I misseated that one, so it seems only the one in the truck when the wires went was effected.
Should it have? - sound like not, but it is used in unknown condition, so I figure it must have been on it's last leg from previous stress and this was the last straw, not sure, truck is running good, and I have spare PCM's so I am figure this a closed issue.