Can't connect to PCM
09-16-2010, 07:19 PM
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Can't connect to PCM
I've been through 2 computers now, suspecting that Amateur Zone may have given me a defective unit. I have power to the PCM relay and it energizes, I have checked the Ground on pin 25 of the harness as well as the positive on pins 55, 71, 97 (they all check out). Checked the diode, and still can't connect to the computer with a code reader. I get no spark unless I disconnect the SPOUT, no Fuel pump (unless I bypass the relay), and no injectors fire.I suspect a wiring harness problem but, I don't know where to start looking. Thanks in advance for any ideas....
1996 Ford F150 5.0
1996 Ford F150 5.0
Last edited by Robert Fortner; 09-16-2010 at 07:20 PM. Reason: Forgot to include make and model
09-19-2010, 02:17 PM
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still no luck
Tried the ignition switch...Still no luck, although I now know how to hotwire my truck....I didn't think it was the ignition since everything else works. (still turns over, radio works, ect..) I seem to have a ghost in the machine, this all started when it started to run rough, would idle fine forever (not in gear) or run at WOT in gear but nothing else. This was with the original computer that autozone returned. I had a mechanic look at it and all the injectors were firing randomly after turning it over (with the engine not turning over anymore) That led me to believe that the computer was bad in the first place, now I have no idea where to look as I can't seem to connect to the computer and I doubt I could have gotten two bad replacements in a row....
09-22-2010, 07:23 PM
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Does the fuel pump relay pull in? Does the PCM relay next to it pull in? They should both click initially when key is in the on position. The PCM relay first, which triggers the fuel pump relay. Almost instantaneous, but the PCM relay must function for the Fuel pump relay to.
09-22-2010, 08:08 PM
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Does the fuel pump relay pull in? Does the PCM relay next to it pull in? They should both click initially when key is in the on position. The PCM relay first, which triggers the fuel pump relay. Almost instantaneous, but the PCM relay must function for the Fuel pump relay to.
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09-22-2010, 08:47 PM
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Fuel Pump Relay doesn't click but will turn on if I bypass it. PCM relay clicks and power is going to the pins that I stated in the first post.....I consider myself a decent shade tree mechanic and I'm in wayyy over my head. Thanks in advance if you can think of anything else I could check!
09-27-2010, 08:39 PM
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You nailed it....the light bulb was burned out! However, I have replaced it and it still doesn't come on...I get brake, ABS, but no check engine light. Is there no way to test a computer to see if it's good? Can't find a friend with 1996 f-150 to swap computers...Thinking at this point I need to beg a running truck off Craigslist! I have checked all the + and - points on the harness to the computer and they all seem to check out....I used this diagram as the link on Ford Fuel injection only seems to go to 1995....