Erratic voltmeter and speedometer

[btrexler]

Have just replaced the PCM on 92 w-250 after the original let the alternator quit charging, would not let overdrive engage, and all dash lights would occasionally stay on then go out. I replaced it with a remanufactured unit and after a day and probably 25 miles thinking that everything was ok, the voltmeter has started going from normal at times to around 10v and the speedometer stays at 0 then jumps to actual speed and then back to 0. Everything else including overdrive works fine. Have checked all ground circuits and they appear to be OK. I'm thinking I probably got a "remanufactured" unit with a problem.

 

[Firstgenfanantic]

You might want to check your cps (crank position sensor). This item has a specified "gap" distance that must be maintained. Often this sensor gets bumped or loosened, therefore causing charging issues and other electrical items to act up.

 

[PToombs]

The gap for the CPS is . 050. Check the plug going to it, just below the head on the front of the engine. Sometimes they get corroded.

 

[btrexler]

Pcm

Removed the Crankshaft Position Sensor and cleaned all parts and re-installed setting at the proper gap. No change. Finally called the parts house where I got this replacement, and they agreed to get another PCM after some serious discussion. I put the 2nd replacement on, and finally, everything works like it is suppose to. I'm not sure about the intake heaters though since it hasn't been below 45 degrees, and they haven't cycled yet. On the previous PCM's, it seemed like they cycled some at about 45 degrees. I'll know in the next few days. I'm not happy even with the "good" replacement, because it doesn't hardly qualify for a rebuilt unit in my book. After removing the cover, it appears that part of the rubber like covering that covers the PC board is removed and new componets soldered to the PC board, then covered with silicone. Not all componets are replaced, and most of the remaining rubber like substance has cracks that are consistant with age and heat, possibly allowing moisture to access the PC board. This unit has a limited lifetime warranty (1 year). After searching the web, I've located a place in Florida that has a replacement (lifetime) for only about $50 more that what I paid for what I have now.