MAP NOT WORKING?

[MUDWHISTLE]

I want to see if my map sensor was working correctly cause I don't think it is. I connected to the ground and the signal wire from the map sensor with my fluke meter and ran it through the pass window and drove it. As I was driving it The signal voltage never changed from 2.35 volts give or take. Even at idle this is what I had. It did not change even as the boost climbed to 25 lbs. I'm now wondering if my map sensor is not working. Anyone got any ideas.?

 

[DaveBen]

It is working because your engine is running. This is one of those items that if it isn't working, the engine will not run. Sorry to spoil your theory. BUT if I am off base someone will jump in me big time.

Dave

 

[Patrick Feeley]

If I'm not mistaken, the MAP sensor outputs a variable frequency signal (vice voltage) that corresponds to the boost. Have you tried running with the electrical connection to the MAP disconnected? It will set a CEL, but if it runs better unhooked, your sensor could be bad. Cheers!

 

[MUDWHISTLE]

It runs the same when it is unhooked, I am curious as to what the computer uses to see that the boost is rising if the voltage doesn't change to deliver more fuel to the engine as it increases. I have tricked the boost sensor on a cat engine and made the computer see 22 lbs of boost at idle and it will deliver full fuel from idle an up when accelerating. Makes alot of black smoke but does take off faster from a stop light. Does someone have a link to how the map sensor works?

 

[DaveBen]

Well, I stand corrected. Sorry.

Dave

 

[Patrick Feeley]

Straight out of the service manuals:

"The manifold absolute pressure sensor (MAP sensor) (9F479) is used on some applications. The MAP sensor measures the pressure in the intake manifold (9424) and provides this information as a variable frequency signal to the powertrain control module (PCM) (12A650). With the Ignition Switch in the KEY ON/ENGINE OFF position, the manifold absolute pressure sensor will indicate the barometric pressure in the intake manifold. The MAP sensor is used to indicate boost pressure on the diesel engine."

Hope that explains it better than my previous description! Cheers!

 

[MUDWHISTLE]

I see thanks for the information.