04.5 ECM not communicating with scanner
 

My truck runs and there is no loss of power but it has a little rough idle and blowing a little blackish white smoke. My mechanic used 4 different scan tools on it and the doesn't communicate with the computer. We bought a new ECM and doesn't communicate with that one either. Any ideas would be greatly appreciated.

You'll have to find a wiring diagram for the truck's diagnostic connector and test the circuits. Verify that it has 12 volts and ground at the proper pins, and check the bus high and low circuits back to where they originate with an ohmmeter. With power off, I believe they should have 60 ohms resistance between the two, at the diagnostic connector.