If there is no sign of chafing from the shield on the wires, there was a TSB issued for this, then you are looking at a bad computer given the stated symptoms.

To double check the chafing issue I would disconnect the ICM and computer connectors, then use a DVM set to ohms on the SPOUT signal wire. Reference the meter to ground. Start wiggling the wires leading to the ICM and then on to the computer to verify the shield is not pulling a signal to ground intermittently. If that is good, do the same for the PIP signal. Replacing parts gets old, frustrating and expensive. Testing to find something empirical at least may save some sanity.

 

This thread summary might help https://www.ford-trucks.com/forums/1...xperience.html

 

You asked about a PIP tester.

This is what I cobbled together from a diagram on site.

You don't need the plug, alligator clips will work.

 

Will do, I will run through the harness and ohm them out. Saving my sanity is a must here lol.

 

That is extremely helpful, thank you so much.

 

I believe that one is for the remote mounded module, I am sorry I should have specified that it is the distributor mounted module.

 

Principal is the same. Maybe some one will post the test connections needed.

 

Sounds good I will look into preforming the test. Thank you.

 

Best diagram I have for the ignition system on a 1991:

 

Sorry for my horrific hand writing lol, I was in a super big hurry. I just copied what the scope was reading for a second and jotted it down.

The O scope came in the mail today and I was able to run some quick tests, I will upload some pictures of the O scope its self later as I don't have them. But I believe I may have pinned it down. The signal from the PIP doesn't look right at all. It looks like the computer is recognizing the signal and is giving a signal back to the TFI to fire the coil.

I am thinking that the PIP may be failing or there is something physically wrong with the dizzy itself, ie shaft play or the vane is magnetized.

 

Thank you.

 

Alright update.
Turns out my idea that the pip was the cause of this was wrong, the connector to the o scope had trash in it so I wasn't getting an accurate reading. I spent several hours again on it tonight, the PIP signal looks fantastic now the connectors are not being interfered with, when the truck is stalled it is still there and looks good. The spout signal is working great too,even in the stalled state, referenced them on the same graph and they line up. Checked the voltage into the TFI and it checks out, checked the start voltage to it when it is being started and it checks out as well. Everything pertaining to the ignition system is good except the coil negative or the IDM. When the truck stalls it won't start back up unless the key is cycled off and then back on again. When the truck stalls the coil negative is gone completely, its not at the coil, and its not at the output of the TFI. This leads me to suspect the TFI is grounding this signal, but I have gone through several of them, even a motorcraft one, none of them have fixed this issue. I did a sanity check on the harness and found nothing. I did find out that the IDM circuit works because it gave me a good shock, its just when the truck dies the signal is gone.

I am going focus on all the other electrical systems of the truck itself. I am going to check the entire computer, I am going to trace out all the wires that involve the ignition system to the eec and see if there is anything going on inside it, I replaced the caps that leak back in November of last year, maybe one of them blew up or something and I need to check capacitance of the caps themselves. I also have also ohmed out all the grounds for the entire truck. I am also going to check the wiring inside the dash I have some other minor issues that lead me to believe something is funny inside there. Also I don't have a great way of ruling out the distributor itself, I am sick of throwing money at it, so I want to confirm there is something wrong with the distributor before I buy a new one.

The only things that are effected by the key that are somewhat related to the ignition system are the TFI module, and the computer. I can throw my other computer that I have, although it doesn't work worth a damn, in it and see if it stops the stalling. Although the stalling did get a lot worse after I swapped the old computer back in it compared to when it was in it before the new computer was switched in.

The battery is brand new, the ignition switch is brand new, the starter relay and connections are all new, the grounds are cleaned, the alternator was just replaced earlier this year, the only electrical faults are this intermittent stalling, windows, windshield wipers and a handful of other minor things.

I am at a complete loss, everything should be working correctly and 99% of it does but there is a reason that it just dies and won't start back up and it won't fire the coil negative. There is nothing that currently points to a failure of the ignition system that I can measure with a DMM or an O-scope. I am gonna lose it with this truck one of these days, I hope this is the problem to end all problems and once I get it figured out it will be smooth sailing. Thank you guys for yalls help, I know we can get it figured out.

 

I have read this forum summery a couple of times, which is extremely helpful but I revisited it today and I am having all the same problems that OP has. I did order this motorcraft TFI from rockauto maybe the discrepancy is the motorcraft module from RA. I did swap a TFI in from local parts store, it was a standard ignition. That's what's in it right now.

Is there any way to bench test it, there is a resistance measurement test in the haynes manual, but it isn't in depth. Any thoughts?

 

Test #5: Ford EEC-IV/TFI-IV Electronic Engine Control Troubleshooting

 

There are pinpoint tests for code 212 in the PCED
Boils down to wiggle testing the harness with a Super Star II tester, after doing a few pinpoint wiring tests
I have those pinpoint tests if you want me to post them