Hey All, happy St. Patty's day,

During a recent issue (TFI mod failure) I attempted the EEC self test to get the trouble codes. I followed the directions for the self test from the Haynes manual, it told me to connect the test light to the POS side of the battery.

If memory serves (hindsight) it was supposed to be the NEG side, and web sight research have backed that thought up.

It sparked a bit when I connected to wire to the battery (from the EEC self test connector) I did not think much of it. I hopped in the cab and the check eng light was on, with no key in..... I put key in, waited for the codes, nothing. Check eng light just stayed on. Then I smelt "burnt electronics" got out of and unhooked the wire.

Now I have no Check eng light, Cruse control does not work, truck bogs down when I hit the accelerator. I fear I killed the Comp. It had full 12 volts running through it for 2 minutes or so.

Has anyone done the self test like the Haynes 87-95 F-series and Bronco before and had this issue? Or is the a way to test that the ECM still works without the EEC or check eng light. I am a bit over my head on this.

I understand the ECM is only 2 bolts and a wiring harness, But if I get one at a junk yard I will need to confirm it works and well, and I don't like bolt and pray mechanics. If some one has a "Pin Voltage Chart" for my truck it would be greatly appreciated.

1990 F-150 XLT 4X4 300 IL6 manual.

Thanks, God Bless,
Stan

 

It was supposed to be hooked to the positive side. The pcm is a ground side switched system. That means all sensors have voltage all the time, and the pcm just provides the ground signal to make things work. You have shorted something, try checking the pcm relay, fuses, fusible links, etc. By the way, easiest way to check codes on the EEC IV is to connect a ground wire to the little gray pigtail at the self test connector, turn on the key, and count the check engine light flashes. If you get a pcm from a junkyard, it has to come from a truck with the same engine/trans combo as yours.

 

Thanks bigbronc,

Where is the pcm relay box, I don't know how I keep overlooking the thing. It is 4 X 12 or so right? I checked the fuse panel and all were good (I used the Digital MM).

Thanks,
Stan

 

You do not ground any pins from the self-test connector. To run the self-test only ground the single (1) wire STI plug to run the self-test like bigbronc said.

Location of the PCM Computer:
http://i54.photobucket.com/albums/g9...CMlocation.jpg

The PCM PLUG:
http://i54.photobucket.com/albums/g9...995PCMPLug.jpg


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Also you have to match the ECM to your VIN #. There are like 13 or 14 different ECM's for these trucks. I got a rebuilt one for my 93 from here www.autocomputerexchange.com. You can get a re-man one or have yours rebuilt. I have dealt with them before with my truck and a friends PT Cruiser the service is fast and they are reasonable.
Kenny

 

The pcm for a 90 truck only has to match the engine/trans combo to the truck that it is going into. You lucked out, 6 cyl man trans 4x4. As long as the pcm is for a 6 cyl man trans, you'll be fine. Doesn't matter whether it is 4x4 or not. I would get a used one to start with. Make sure the numbers match what you have, and it doesn't have a similar "smell". Just plug it in, self test it, then see if it will run. I wouldn't mount it in place until it is all good.