OK so here's the problem. The van will just shut off, completely randomly. I could be driving down the road or just idling in my yard and it will shut off. It could be a cold start, or warm start. There is no spuddering, dying sound, nothing. Just shuts off. It started a couple months ago and back then it would run for like 3 days straight without any problems, over time it got worse. Its to the point where it stalls now, at least 6 times a day, lasting only a few minutes each time....
1997 ford e150 5.4 triton. Mileage is around 130k. Here is a list of things we have already done to it:
Replaced-
Battery
Altinator
Crank shaft sensor
Cam shaft sensor
Throttle positioning sensor
PCM relay
Fuel pump relay
PCM diode
Had aftermarket security system, which we disconnected and replaced original wiring
Ignition in column replaced
Replaced PCM itself

When the van shuts down there is no power to the pcm. We put scanner on it and only got a code for the egr valve so we left it running with the scanner on it and waited for the van to shut down, and when it did shut off, the scanner got no power. Also, the fuse which goes through the cigarette lighter does not pop which runs the power port where the scanner plugs in under the dash, and when I turn off the key and turn it back on the scanner comes back on with no codes and the van starts back up.

 

Newer that my era, But, first thought.........

Bad grounds, from battery to engine/body.

You mentioned that you replaced the 'Ignition in column' the key switch or the ignition switch on the lower end of the steering column?

Still, if you loosing power to the ECM (what your calling the PCM) that would indicate a bad ground wire, the battery (which every thing runs off of) is loosing connection, shutting down the engine, and as you wrote, turning off the power to your OBD scanner.

What condition was the ECM connector??

 

In the steering column we replaced the connector (plugin) under the column. And the PCM connector was in good condition, no frayed wiring or exposed wiring. We actually set up a hot-wire to the main power and ground to the PCM to make sure it was getting the power it needed, and still did not solve the issue.

 

I've been through the same thing with a Car......You have a dead short in in the harness or connectors for anything in the PCM system. The PCM will turn itself off if a short is detected (anywhere) and without codes, and if it's a vibration related short it should restart right back up like nothing happened.

 

So what exactly do you suggest I do?

 

Also I have moved the wires around on the harness while the van was running before, and there was no change.

 

For some reason the idea of a failing ECM strikes me about all this. There are capacitors inside the case that can and do go bad which has the possibility of leaking onto the PCB and creating more problems.

Since this failure causes an inability to read the ECM that's a strong suggestion its internal to that device rather than interconnecting wiring being an issue.

 

Agree, But, OP wrote -"Replaced PCM itself"

Unless.........it's a Used EMC??? Then your spot on.

 

Anything that has a (Sensor) is fair game for a short........on that car it was a Oxygen Senor wire shorting on a Trans Bracket under the car. Another car had a Power Antenna that would go up and down by itself just setting there, the Main Harness Block was loose at the Firewall. I had a car that rusted off just one pin on the Temp Sensor and would Idle at 3000 RPMs hot......sure scared the Wife....LOL

 

And clean your MAF sensor, Throttle plate, and EGR passages while your in there, assuming it's had plugs and coils changed already at 100,000