Technical help needed

Discussion in 'Engine & Performance' started by Rider48, Jun 14, 2015.

  1. Rider48

    Rider48 Junior Member

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    Jun 14, 2015
    I am new to the forum but after struggling for over a week (evenings and weekends) to fix my truck, I need a little help from others.
    Long story short, 1998 F150XL 4.6 auto 2wd, non-PATS, non-COP (125,000 miles), died suddenly while driving without prior symptoms. Threw codes for failed coil pack A and D. Metered coils as per manual and proved within spec. Swapped in new coils to see, no difference. Trying to start it seemed more a fuel issue, sometimes starting with terrible idle, and never running longer than a few seconds. Not understanding how 1/2 of each coil pack could fail simultaneously, I tested fuel system as precaution, good pressure that holds, filter changed. Went back to chasing ignition/electrical. All fuses good. Power at both coil packs as it should be on center pin. Here is where it finally makes some sense; testing reference signal for coil packs while cranking with LED test light. Unplugged pass-side to test: A-good, B-good, then when unplugged other coil to test while cranking, truck started and idled (rough) while testing C which was ok. Testing D shows no reference signal, in fact short to ground. Disconnected harness at PCM to prove reference wire, no shorts or ground, indicating trouble in PCM. Removed reference wire for coil D from harness plug at coil at connected. Truck starts, runs, drives, even idles with a slight lope on 6 cylinders. The only code it throws is for failed coil D. In my opinion I have proved PCM as problem. Ford does not sell replacements but lists it as reprogrammable
    My questions are as follows.
    1. Would flashing existing PCM solve this or is replacement required?
    2. When sourcing wrecker part, would PCM from truck with same options plug-and-play or require flash?
    3. If not from truck with same options, and requiring flash, what PCM will work? I have read that the donor part must come from vehicle with same trans, and elsewhere that 5.4 and 4.6 are interchangeable to some degree. If flashing, how much of this is true? More specifically, I have a parts truck with 4.2 V6, same auto trans, but it's '99 so it also has PATS. Would this PCM be able to be flashed and work for me? Or am I relegated to finding pre-PATS, 4.6, auto PCM only?
    4. Is Ford able to flash PCM on bench, not in/with truck? Truck is some 40 miles from dealer. Installing new PCM would cripple it, requiring a tow, or I would have to drive it on 6 as is, and install new PCM in parking lot before flash; the alternative, paying them to install.
    Has anyone experienced this?

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