I have 1990 D 150 with a 318. If I plug in the Map sensor, I lose power to the coil, fuel pump and the check engine light will not come on. If I unplug the Map sensor, Coil turns on, fuel pump and engine light come on. The truck will then start but runs poorly. As soon as i plug in the Map it dies. I have replaced the Map sensor, same result. I also pulled the computer and put it in my '91, it ran just fine, so not a computer issue. I don't know what else to check. Anyone have any ideas?

 

When you say "plug in map sensor" you are talking about the electrical connector correct?
There could be a short somewhere in map sensor wiring.
Is the vaccum line to it hooked up and not leaking?

Dave

 

Correct, I mean the connector. I've tried a different harness as well. It all started after getting the heads rebuilt. The truck ran great, just smoked. Pulled her in the garage took the heads off had them rebuilt, put it back togther. That's when the problem started. I had no spark no fuel. The ASD would not turn anything on. Replaced the Hall effect, still nothing. We took the wiring harness off, the half from the engine to the right inner fender well where in connects to the other half. That's when we figured out that now the ASD would turn things on. We started plugging in connectors one at a time then turn the key on to make sure we still had spark and fuel. Everything keep working until we plugged in the Map. Not only is there no spark, the check engine wont even come on. The harness is grounded to the intake, the intake is grounded to the firewall, do I need to add one from the Battery to the engine? I'm just out of ideas of what to try next. This is my first Dodge, bought it for my son, he turns 16 next week.

 

There should be about 6 gauge cable running from the negative post of battry to the engine block.
Have you check that harness that the map sensor harness plugs into going to the computer to see if anything is shorted or melted together?

Dave

 

Yes, plus I tried a different harness. The first thing we did before we took the engine apart was disconnect the Battery. Very frustrating.

 

I am out of Ideas.
Seems like there is a short somewhere.

Dave