right now my alternator, AC and cruse all are not working. All are ran off the computer. i thought the the computer gets its signal from the crankshaft position sensor which is also the tach sensor for our trucks. am i correct there?
my tach sensor/crank sensor is not working and disconnected right now which i thought was my problem for the computer not functioning but 94cummins12v said he unplugged his sensor completely and his computer was working just fine his AC worked and his alternator still pumped out 13.8v at idle.

what im needing to know is if the computer is sensing it off that tach sensor or is it something diffrent and i have a short or broken wire or maybe my computer is just toast?

 

I'd say you need a PCM , but you might check the grounds on it. Some had external ground leads, some did not. Each componet that the PCM controls is independent of the next. While connected in the power source and ground source and voltage regulation circuts tach signal has NO effect what so ever over the other componets. It does control Instrument panel functions and such.

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PS it will prevent AC from kicking at a low RPM (starting conditions)

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Again ,
If you've got your crank sensor plug in your hand (sensor Side, Top pin in triangle facing left) , the top pin in the triangle should be Red or white, This is your power source for the sensor .5V IIRC, the pin on the bottom should be black ,This is your signal wire to the pcm, light blue should be on the top, this is your sensor ground. Match all wire colors and see what you get!

 

well on the sensor side the plug was ripped out. the sensors wires are all black no differentiation but on the harness side there is an orange which is the center wire/pin and then the ground is black with a white stripe but im not sure which side it goes to on the sensor. the other wire is white with a black stripe.

so are you saying the tach controls the AC and thats why it wont turn on? if that is what your saying then how does 94cummins12v AC work when he unplugged his tach?

 

Okay, Well the best route is to put a new sensor on it.
The PCM controls the AC clutch with the Crank sensor ONLY for the first 60 seconds of opperation according to the manual.

 

hmmm well my ac wouldnt work when i turned it on and it was definatly after the first 60 seconds of running. after i get a sensor im gonna probably have to try a new PCM. if i can find someone around here that will let me plug in there computer ill be trying that before buying one but if not ill just have to buy one and hope it was the problem.

my only other guess is a short/cut wire but it was running fine before pulling the head other then the cruse started freaking out. after i set it then it would randomly turn off and i would reset it and it would do the same thing.