Update

S

six_wheeler

New member
Ok, just yesterday the electrician finally found the culprit: One of the three wires on the (modified) connector of the MAP sensor was shorted out.
After the new computer arrived and all the sensors (TPS, MAP, IAT...) had been replaced, the new computer still gave fault codes on all of them. The truck idled rough with lots of black smoke and no revving up (this is before and after having rebuilt the engine last week.) Yesterday he showed it to me: grounding one of the wires made the engine idle perfectly and rev up nicely. Now he's gonna trace the wire through the harness and see what the heck is wrong with it. Then we're gonna run another code scan.

Shady
 
VermontTy

VermontTy

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Re: Update

Ask what wire it was; location and color. I rebuilt my entire truck harness from scratch using only wiring diagrams. I might be able to help out.
 
VermontTy

VermontTy

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Re: Update

Most likely its the black...MAP has 3 lines; gray, black and light green.

Gray = 5-volt reference line, outputs 5V from the ECM.
Light Green = MAP signal, ECM reads this to determine manifold pressure
Black = MAP ground, this is shared with the black wire on the coolant temp sensor on the front of the intake manifold.

A quick sanity check for your electrician is to ohm out between the black on the MAP, and the black on that coolant temp sensor. If they are not tied together, that is your issue. Both of those grounds run back to the ECM to provide the reference ground for both MAP and CTS signals.

So you have reference 5V, reference GND, and the signal. Most likely if he grounds one and it runs like a champ, its the black one....
 
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