I have a 1986 2.8l v6. The voltage going to my map sensor is 5v, good ground (at least I think) When the car is at idle it reads 1.9v at the b terminal on the map. When I go to WOT (wide open throttle) it drops to .6v. ITS BASS ACKWORDS. I know the voltage coming from the Map to the ecm (b terminal) is supposed to increase when throttle increases, it's doing the exact opposite. What would cause that?

Thanks,

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Um, it's bad?
My guess would be it's not actually trying to go backwards, just voltage drop or gremlins are sucking some juice at WOT. Maybe there's a short or something..
(I have no idea what I'm talking about )

Are you sure you have a map and not a vac (from a carb'd car)? They work backwards. Otherwise, the ground is bad or the +5V from the ECM is being sucked down.

Did you verify the wiring from the map to the ECM? Could someone have rewired it for some diabolical reason?

I checked the power to it while running and it had 5v. Just the volts going out of it was haywire. My next option would be to jumper a wire from the 5v to map and ground to map. This would leave the center terminal open and I can test the map isolated from the system and see if it's still doing the same.

No rewiring was done. I know I asked for a map sensor when I was at the auto parts store (all 4 times), and it fit perfect. There shouldn't be an ADV off a carbed car on mine it looks just like a MAP.

To read MAP voltage you must measure between pin B and ground with the wire (B) disconnected from the ECM or the reading will not be accurate.

The MAP and TPS share the same signal voltage so if the TPS is bad or shorting out there is your problem.

I think it's time for you to take this to a shop you trust and have them hook it up to a scanner and see what the REAL voltage is at the map at idle and at WOT. You've been thru enough maps. I've got a feeling that you have a bad ground or a degraded 5v signal to the map. Time to stop the BS and get the sucker fixed. Glad to help in any way I can dude!

Phil

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GTDude
OVER 25 years GM experience

Well, if the connector fit, it's probably the right one. I agree with GTDude, you need an independent view of the problem at this point. Sometimes you get into a loop and overlook the obvious.

You should definitely be able to read the map output with the ECM connected.

Bill's got a point there about the TPS. What does the +5V read at WOT? Maybe it *is* dragging the +5V down.

[This message has been edited by terryk (edited 07-03-2002).]