moparman13045

Im not sure whats going on but in my 1992 W250 I had been having what seemed like symptoms of a bad pcm or Crank position sensor. I have no overdrive, no a/c, no alternator charging, and no heater grids at startup. I ordered a replacement PCM, installed that with no change at all, I then replaced the crankshaft sensor as well, twice, to rule out a faulty one from the parts store, and no change again, what gives? I even tried swapping the ASD and A/C relays with no luck either. I just don't know what to try next? I need some ideas please, and thank you in advance!
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Onemoparnut

Did you test for power like it says to do in the sticky?

moparman13045

yes and some of the values aren't correct on my truck

Onemoparnut

Have you checked the fusable links?

JimmieD

Single most common problem in electrical and electronic systems: bad grounds. Where any component or device is mounted to a body panel for ground the panel has to have ground continuity back to engine block and battery ground. Sometimes necessary to run ground jumper wires panel to panel, and of large enough wire to carry the load, at least 12 ga, 10 ga is better.

tacoAGGIE

Where did you order your new PCM?

thrashingcows

Did you try replacing the 3 relays on your drivers side inner fender. One if for the A/C, one is for Charging, and the last is a relay for the starter system.

There might be other systems they control as well???

moparman13045

Thanks guys I bought the PCM on rock auto. Ill have to clean some of the grounds up some more or add auxiliary ones. When I tested the PCM, I got no voltage at the #3 terminal which is constant feed. With the key on I did have 12v at the #9 terminal. At grounds 11 and 12 terminal I had .4 and .3 ohms.

I did switch the relays but I haven't replaced them ever. Thanks in advance

gyman98

Check for wire breaks/continuity on CPS wiring as already mentioned, bad grounds and fusible links. All else fails just keep tracing wires, you'll find the problem. Is the CPS set properly? Bulkhead at firewall and PCM clean and secure?

j_martin

With no voltage at #3, the PCM will not operate. What's the mystery?

Bad fusible link or wire.