Hi every one I have installed the replacement ECM/ECU my truck runs great.

Thank you.

Although I still cannot figure out way I only have 6 volts in my PIP wire and 4 volts in my last wire.

I was told that I should have full 12 volts on my PIP wire and no volts on my bottom wire.

does anybody know? (should I start a new thread for this matter?)

 

I hooked up a Ignition test setup on the bench today like you have on your truck.
The PIP wire (top wire) was one volt below power supply voltage and the ground wire (bottom wire) was at zero volts. Distributo not turning.

Note I did not have this hooked to a Computer and was rotating the distributor by hand and had good spark.

I will put the distributor in a Sun Distrib-U-Scope to spin it in the morning and see what wave forms I get on the Tektronix scope. I will let you know what voltages I get also.

 

Right on!!

this is what I found, I had unplugged, my gray plug at the finder wheel well that goes to my ICM, I did a continuity test between ICM and the opposite end, all wires good no short.

I Tested the plug to the computer Key off continuity was good but when I have KOEO it shows a short on the ground wire. So I was thinking it could be my ignition switch

I have taken my ignition off and found that their was a short in the switch, I pulled the other ignition switch from my parts truck, it tested good (no short). I haven't installed it, because I am having a B**ch of a time getting my steering cover off to replace my actuator rod. I'm about to pull the whole steering Colum out That would be a lot easer then replacing the actuator rod, I have a good steering Colum in my parts truck.

 

Is your ICM/TFI mounted on the distributor or on the drivers front fender?

 

On my distributor.

so I tested between the ICM/TFI plug too where it plugs in the computer harness

 

After installing the new ignition switch, I still have the 4.30 Volts in my bottom wire, I also have only 4 volts in my top wire.

I am going to pull my ECU/ECM plug to see what happens.

I am going cuckoo over this.

 

OK I cut my bottom wire of the TFI/ICM that is supposed to be ground wire, and grounded it to the negative post on the battery, it did not start, I hooked up the wire back to the original wire and it starts fine.

using my voltage meter, running from the positive post of the battery to the bottom wire I get 7 volts, but if I go from the negative post of the battery I get 4.3 volts.

 

Update:

After reconnecting my ground wire on the ICM/TFI, I started my truck, then tested the negative wire, there was no volts on it. after it starts the high voltage changes to negative volts.

I don't know if that's right or not but it sure is different.

 

Maybe these two diagrams below will help.





/

 

Yes that helps, I want books like that, that's great information thank you Subford.

where can I get books like that?

 

Ebay or Helm.inc.
The images are from the 1990 Ford Truck Electrical & Vacuum Trouble-Shooting Manual but your 1991 should be the same.
Get the 1991 if you can for yours.

 

I drove my truck to town, ran great.

I am still puzzled why I get 4 volts KOEO and 0 volts KOER.

Thank you for all your time, getting me through this pragmatic issues