Well, my disaster of the last week and a half seems to be over (knock on wood). I thought I might share as I haven't seen other threads with the same issue through the searches I have tried.

My truck dropped 4 cylinders the other day about a 1/4 mile from my house. Just all of the sudden 4,5,6,and 8 died. I pulled over because it just started running so bad. Barely idling with nothing visibly wrong I limped back to the house. The converter was extremely hot. I have to leave it sitting to catch a flight.

When I got back from my trip I started testing things and looking for answers. The codes showed the COPS not firing so I bought one new one and it made no difference. After getting a friend over we traced it back to the PCM. He went back to some program he has and found that the 4 pins that operate those cylinders are all in a line and on the bottom of the PCM connector plug. Certainly seems like we had a fried PCM. WE checked continuity in the wires from the plug to the COPS and it was good so I set out after a PCM.

Found one in a junkyard and spent 3 hours riding up and back on my motorcycle (cold it was!). Replaced it and the truck turned over but wouldn't start at all. So, I bought one from NAPA. Turns out it has to be "flashed" so I checked with the dealer to see if they could do it. Got up early, picked up the PCM from NAPA rode the bike (REALLY cold) to the dealer where they informed me it "had to be in the truck!" Duh? If the truck ran, I wouldn't need it flashed! So, back to NAPA where it was sent away to be programmed.

Got back from another trip and installed the computer last night. Truck wouldn't start. But, it occurred to me, from some posts on here, that maybe the PATS system wasn't coded correctly with a new PCM. So, got a locksmith out today and he cleared both the PCM and the cluster and then re-coded to my keys, and, wallah! it runs again. Re-installed my Diablo tune and it runs like a top. As the truck just turned 200k, I changed all the plugs in the process and hopefully it will be good to go for a long time to come. I also have a spare PCM now if I ever need another one. No use returning it to the junkyard - the gas alone is about as much as they charged me for the part.

I do hate electrical problems.

 

This is good info to know, and if I ever meet ya I'll buy you a beer for going through the trouble for the rest of us to learn from, lol.

So what you're saying is that you think the junkyard one would have worked if you would have got it coded for the PATS system?

 

Just this evening, my truck developed the same fault type losing cylinders 1,2,3 and 7 all at the same time.
The codes are P0351, 0352, 0353 and 0357.
When it happened the CEL did not come on while running but once turned off and restarted the CEL lamp came on.
My on Dash monitor was able to read the codes and verfied by a good scanner.
Cylinder 7 trapped the fault and stored the info when it happened..
A look at the service disc shows all these cylinders coils are harnessed through the same cable.
The others are harnessed through a different cable.
My suspision is also a PCM fault.
I will do some testing to verfiy this is the case.
Will have the truck hauled to the dealer monday for the replacment and programming unless they find it less than a faulty PCM.
Happens to the best of us.
Good to hear you got squared away but with a learning curve.
The problem you had was the VID block has to be programed in any replacment PCM and Keys/Pats to match.
Good luck.

 

so the problem is INSIDE the PCM. You dont see anything wrong with the plug or harness end ???

 

Yes, definitely inside the PCM. I actually took it apart and couldn't see anything "burned" in the circuitry, but I am no expert in that area. We did continuity checks on the wires from the PCM to the coils and everything checked fine. They are hot all the time and the PCM becomes the "ground" to make them fire, I guess.

It sounds like Bluegrass has the exact same problem on different cylinders and I suspect (from reading his posts) that he will give a much better analysis of the situation.

 

Yeah, I think it would have worked and am probably just going to keep it. It would cost me almost as much to return it as it actually cost, so having an extra might not be a bad idea. The locksmith only charged me $60 to re-program the keys so it would be worth it to hang on to the PCM in case it every happens again - better not though!

 

Here is how to test the PCM switches.
Cut the connector off an old coil and solder leads on the exposed area.
Connect the coil plug to the test lead.
With a volt meter, look at the red lead to ground with the ignition on. It should read the battery voltage if the fuse is good or there is no open circuit.
On the other lead, measure the resistance looking back at the PCM switch for that cylinder. It must read an open or very high resistance. If a very low resistance, the switch in the PCM for that cylinder is shorted.
A second issue that could happen is the switch is not being controlled.
In that case, disable the fuel pump then crank the motor over to see if you can see the switch supplying ground when the fire order comes around to that cylinder.
So far in my problem, a coil was blown apart and the switch is shorted on cylinder 3. The code for it is 0353.
I think the switch short in the PCM burned the coil from excessive constant current.
It has yet to be fully worked out.
Seems when I get a problem it's a dilly.

 

I really have no problem admitting that the previous information is significantly over my electrical understanding and ability. I do appreciate people like you being in the world and on this forum. I'm just glad mine is running like a top again and I wish you the very best in figuring yours out. I'd be throwin parts at it by this point.