CALLING ALL PCM MASTER MINDS - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

 
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post #1 of 7 (permalink) Old 10-21-2018, 10:26 AM Thread Starter
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CALLING ALL PCM MASTER MINDS

96’ bone stock F250. Been having what I would consider typical CPS problems (quick cut outs, and died a couple times but restarted no problem). Then Tuesday ran great for a couple hours then went to leave again a few hours later and NO START. Fired up once for a split second but that was it. No tach so swaped in a spare CPS and exact same thing. One fire up out of a bunch of attempts. Paying more attention to the tach notice it works some crankings and not at all on others. Assuming wiring prob now I test CPS pigtail, ground-good, 5V-good, next wire is different every time 6v 4v 3v 5v. Checked my 99’ and found it’s supposed to be battery voltage. Googled wiring diagrams to help find the trouble spot. Found that diagrams are slightly wrong, they say the green wire in question goes through pin #39 in the 42 pin connector and ends at pin #21 at the PCM. The #39part is right but it ends at pin #49 at the PCM, not #21,21 is an empty hole. That one Ohm’d out perfect but ironically the other two wires were high at 25 Ohm’s. Jumpered a wire from the battery + to the unplugged #49 PCM connector and got perfect battery voltage at the CPS connector.

So do I assume PCM is not putting out the Battery + its supposed to at Pin #49 ??? =New PCM

Is there a way to very carefully “hotwire” the PCM (with it unplugged) on the proper pins to check/verify the voltage coming out of pin #49 ???

Would the PCM out of my 99’ work in the 96’ just to see if it will run, without blowing something up ???

Could I run a wire from the battery+ and splice it into this wire to supply the needed voltage ??? If so would I need to cut the wire going into pin #49 to keep from back feeding the PCM and causing more damage ???

ANY help is greatly appreciated. I NEED THIS TRUCK RUNNING.
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post #2 of 7 (permalink) Old 10-21-2018, 11:53 AM
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What PCM is in it (DPC-202 or DPC-203)? What diagram are you referencing? PCM pin 21 for the CPS Dark Green wire would be for a 97 California splitshot OBS that is running a DPC-311 or 312 PCM. PCM pin 49 would be the correct pin for a 96 OBS truck. I would start with the CPS and PCM disconnected and see if you get any shorts to ground, power, or open circuits by jostling the harness and 42=pin connector. The 99 PCM will not work at all (pinouts would be completely different). Cheers!

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Last edited by Patrick Feeley; 10-21-2018 at 10:13 PM. Reason: Should have been DPC-203
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post #3 of 7 (permalink) Old 10-21-2018, 03:18 PM Thread Starter
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Not sure on the 202 or 203, have to pull it out to see right? I dont know what the diagram went to (your probably right) the image was "protected" so I couldn't read the top. Jostled and did more testing, dreadfully I think the wiring is all good.

Last edited by QKE-F250; 10-21-2018 at 09:49 PM.
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post #4 of 7 (permalink) Old 10-21-2018, 10:30 PM
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Just so you know, the Dark Green wire is the CPS signal wire and won't simply have 12V on it. The signal that comes from the CPS will be a digital frequency and not a constant 12V. Cheers!

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post #5 of 7 (permalink) Old 10-22-2018, 09:37 PM Thread Starter
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I'd seen references to signal wire and square waves but couldn't and still don't make sense of it. Feal like giving the 411 for dummies on that subject? To possibly explain myself a little better at one time I put the black lead to battery - and the red lead to CPS connector (green wire) and voltage is JUMPING around between 4.5 and 5.5. Does that at all sound right? What's your next step advice?
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post #6 of 7 (permalink) Old 10-23-2018, 09:17 PM
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See the attached. If you are using a DVOM, it'll basically try to average the voltage since it is not steady. Cheers!
Attached Files
File Type: pdf CPS Description.pdf (386.5 KB, 21 views)

97 F250 SC 4x4 (CA model), E4OD, 4.10 LS,
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post #7 of 7 (permalink) Old 11-18-2018, 11:13 PM Thread Starter
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Sorry for the late update. Picked up a pcm at a pick-&-pull and problem solved. Bonus was it smoothed out the hard shifting that I thought was just the norm. Thank you Patrick for help
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