PCM/ECM issue No Voltage at CPS - 1993 W350 5-Speed Help

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PCM/ECM issue No Voltage at CPS - 1993 W350 5-Speed Help

Postby closefan » Sun Nov 03, 2019 6:40 pm

Hey Everyone,

I've done the required 50 hours of research but still cannot figure out whats wrong with my new purchase of an old 1993 W350 4x4 5-Speed Flatbed. I got this at auction so I don't know much.

What I do know:
Most, if not all the wiring is stock. There is no External Voltage Regulator. When I jump the car, it starts right up, but the battery gets no charge. Inside the cab there is a warning buzz and I see the ABS light quickly go on and off and a few other lights, but the Wait to start does NOT shine up. I do live in So.California so it may just be because its not cold. I also don't think this odometer has works since 174k because I drove it around and it doesn't have Speedometer and Odometer doesn't work. I am not sure if the issue was the reason the last owner got rid of this truck. Seems like it was a farm truck and by the Carfax, only had one owner. Could be that the PCM went out and he just decided to write it off. Anyway...

Current Symptoms/Problem/Issue:
I have no charge at my battery. Before you say CPS, or Alternator, I can tell you that I've checked my fusible links and I even removed the stock plastic that was covering each side, they check out fine. I get power all the way to the Alternator. I checked and cleaned all the major grounds. I checked the CPS as best as I could. I basically unplugged the CPS cable on top of the intake and checked Black/blue tracer (ground wire.) OHMs read close to zero to the battery ground. Seems the Tan/yellow tracer is not getting proper voltage. It reads like .05 Volts when the car is on. I went ahead and checked the resistance all the way to the PCM and it read 0. On the PCM I Checked pin #3 (unswitched) and pin #9 (switched) for power and they have power from the battery. I checked pins # 11 &12 for good grounds and they are fine too. I've gone around and checked the wiring as best as I could and didn't find any issues.

Is it the PCM? I have no Full Fielded the Alternator because I do not know how and after reading every forum everywhere, its still not absolutely clear how to do so... at least to me.

This is absolutely super frustrating because I don't know why the CPS does not get that 8 volts it needs from the PCM. It could only mean the PCM is bad. Unless you guys can help me figure this out.

Please, I don't wish to mickey mouse it to an External Voltage reg if I don't have to , and would love to first find out what else could it be if it isn't the CPS.


smoke screw?
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Re: PCM/ECM issue No Voltage at CPS - 1993 W350 5-Speed Help

Postby boomer » Fri Jul 24, 2020 10:56 pm

If you're not getting voltage on cps input...it could be com related but cpm varies voltages. No resistance on cps is a bigy...it should not be near zero...rather very high resistance. But check that on outer pins...in both directions because it behaves like a diode and you will get a reading in one direction but not the other.
fuel screw!!!!
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