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Key on engine off, sensor output connected and not connected to ecm voltage is at 4.8V
engine running, sensor output disconnected from ECM- sensor output voltage is at 2.2V
Engine running, sensor output connected to ecm- sensor output voltage is at 0.02V
This is the reason for the P0107 code which is set when the sensor output is below either 0.2V or 0.5v depending on what you read. Lets find out if its a supply problem, the lack of the ability for the sensor to drive the ECM load or the ECM.
When you get 0,02V sensor output with the sensor connected to the ECM, what do you measure as reference voltage between the two reference wires (5V ref and 5v return)?
What is that same measurement when you disconnect the sensor from the ECM?
OK, you don't have a 5V ref circuit problem. At this point the way to test the pcm is to use a fused jumper wire to disconnect the MAP sensor plug and jumper from 5V ref (+) to the signal output slot and then look on your scan tool to see if the PCM reports the 5V level and/or to see if the fuse blows. If the fuse stays intact and the PCM is reporting 5V then the MAP sensor has failed.
Do you know for sure that you cannot see live MAP data?
Actually if you can see live MAP values in your scan tool we may need to be clever and supply the sensor input to the ECM with a normal idle voltage of 1.0-2.5V because I don't know what the engine will do trying to start with a 5V MAP input which is WOT since the truck needs to run to reproduce the fault. If you cant read MAP values in your scanner we might be able to still use this tailored voltage method because if the truck starts and runs better than its the MAP, if it still runs like crap then its the ECM. If its inconclusive and you are trying to stay away from a big parts price tag then we can move on to your other codes because if you get similar problems with the sensor connected to the ECM then it might be the ECM.
If there is a way to see the MAP values on my scanner, then I can't seem to find it.
Anyway I ran a fused jumper across 5v ref and sensor output. I started the engine and it will actually idle on its own now with out having to give it any throttle to keep it running.
Maybe the ground fault in the original sensor output wire was made the 3 MAP sensors go bad. I should also say it's definitely not running perfect but it is at least staying running. The ecm must not like the full 5v on the sensor output when it's at idle.
The truck has killed three MAP sensors? That's why you always verify all the circuits before you just replace the sensor. There can be shorts to gnd or power, shorts to other signal wires, breaks, poor voltage or grounds, etc.
