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Troubleshooting PCM - 97 F-250 cali emissions.

Discussion in '7.3L Powerstroke Diesels' started by Macrobb, May 26, 2019.

  1. Macrobb

    Macrobb Full Access Member

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    A good friend of mine picked up a '97 F-250 2x4 E4OD with 500K miles on it. Ran pretty darn well, really.

    He convinced a friend of his to loan him an Edge Evolution tuner(94-03 7.3 PSD model). Connect it up, program to race mode... tons of power!

    He then shuts the truck off, switches the programmer to extreme mode. Programs fine, but it won't start anymore.
    Tries to program it back to stock... won't program. Can't figure it out, has it towed home.

    Now, this is where I came in.
    What I saw is:
    1. with key on, EBPV(or something else near the bottom of the turbo) is constantly clicking. Just click-click-click-click.
    2. Unplug PCM relay, the IDM relay now constantly clicks with key on.
    3. Unplug IDM relay and PCM relay - No noise, "check engine" light "pulsing" at a high speed.
    4. Plug PCM relay in, IDM relay not connected - EBPV clicks slower and more inconsistent - like 1 click/second average.

    With PCM relay in, no IDM relay, and another truck connected with heavy jumper cables(for higher voltage), I was able to connect the edge evolution again, and after 3 tries, it finally connected enough to program back to stock. When the edge connected and got the PCM into "program mode", the EBPV stopped clicking and everything went smoothly after that.
    (Note: after programming back to stock, no change. Still clicks fast with both relays in).

    Now, to me, this strikes me as being a PCM power issue of some sort. Either it's not getting enough power, or something the PCM is trying to output is shorting it out, dropping the voltage below it's "reset" voltage, and repeat.

    I've tried:
    1. Checking all fuses with a multimeter.
    2. Found primary power wires to PCM(pins 71 and 97 - both red wires), stripped them back a little, and connected multimeter to them(12.2V or so).
    3. Connected both PCM power wires to the battery using my multimeter's 10A current setting(in parallel with existing circuit). One wire drew .25A, the other nothing. So, the PCM is definitely drawing some power, but again, no change.
    4. One ground wire from the PCM grounds out on the fender just above the PCM. Checked that with multimeter - 0V to battery negative - so we have a good connection there I think.


    Now... what should I check next?
     
  2. trackspeeder

    trackspeeder Stone crusher.

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    Most likely the PCM has fried. Try another PCM.
     
  3. 79jasper

    79jasper Chickenhawk

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    Real common for those cheap tuners to fry a pcm.
    Also pull the idm off and give it a good shake. See if you hear water.
    Once it's back to running and he wants tunes, tell him to get a hydra.

    Sent from my SM-N960U using Tapatalk
     
  4. greenskeeper

    greenskeeper Full Access Member

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    fuel bowl heater disconnected? I forget what fuse is for the PCM/fuel heater on the OBS trucks....I believe it is under the hood maxi fuse.

    Are you getting the "wait to start" light when turning the key to on?
     
  5. Macrobb

    Macrobb Full Access Member

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    Haven't unplugged anything, but did check all fuses throughly.
    Yes. It never goes out. GP relay does not turn on though.
     
  6. 79jasper

    79jasper Chickenhawk

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    That's a sign of no power to pcm. Go ahead and unplug the fuel heater.

    Sent from my SM-N960U using Tapatalk
     
  7. Macrobb

    Macrobb Full Access Member

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    So, followup:
    Contact edge. They ask for model year etc. After they hear it's a '97 cali truck, they go "Oh, yeah, we have issues with that".
    They ask for the code on the computer itself. Once provided with the part codes, Edge ships out a "tune to stock"-programmed computer.
    We had to try it a couple of times to make it work, putting the truck on the charger to keep the voltage up in the 13.5V range, disconnecting the IDM relay(reduces output drain on the PCM), and... it programmed back to stock!

    Crank, and 10 seconds later she fires right up.

    After that, we did(with charger on this time) tune it again, twice in fact. And it tuned just fine. Looks like "low voltage" causes issues with this particular PCM and tuning,and "low voltage" for this PCM is around 13V.
     
  8. Powerstrokin350

    Powerstrokin350 Full Access Member

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    Glad to hear it worked out.
     
  9. bbjordan

    bbjordan Snow Monkey

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    Amazing! :eek:o_O

    Good stuff to know for future reference.

    I don't know if that is what you call "Tech worthy", but it's something I'd like to find in a Tech section, if I were having that problem.
     
  10. Oledirtypearl86

    Oledirtypearl86 Full Access Member

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    I just changed jobs and at the shop I work at we have had this issue with deleting the newer trucks so I started putting a charger on all trucks at 10 amps for a few min before tuni g and after tuning the dodges will really freak out if there isbt a sturdy 13v the whole time
     

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