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Hey guys, I'm at my witt's end trying to get my car to fire and get the dam MAP sensor working.

Car is a 94 mustng GT procharged 363, with and AEM PLUG n' PLAY ECU. I have removed the MAF sensor and installed a GM 3 bar map sensor.

MAP pin out should be:

A-- Sensor Ground
B-- Map output (dedicated on the AEM box on a seperate plug)
C-- 5+ volt refrence

I used the existing wiring from the MAF sensor for the new MAP.

I used these Pins of the MAf connector:

B-- sensor ground (black wire)
D-- 5+ volt signal (light blue w/ a red stripe.

I have checked continuity on all wires and they're good. once the map is plugged in, it just reads -12.4 to -12.8 psi on my laptop screen. even if I put vacuum pump on the MAP, OR blow in it (pressure) my MAp reading does no change. I have tried 4 different MAP sensors. all are the same.

The only thing I can find that seems funny is with the map sensor unplugged, key on; I have 4.78 volts on the 5+ volt refrence wire.

BUT*** once I plug in the MAP sensor to the harness, all I can get is .03-.08 volts.

I'm lost, any input would be greatly appreciated. The car fires up for about 2-3 seconds then dies. Fuel pressure is good. we checked spark, MSD system and distributor phasing. everything seems to be functioning properly.


703 Posts
That's because a MAP sensor reading actual atmospheric pressure in PSI.

At standard sea level the pressure is 14.7 psi or 1 atmosphere (1 bar). At higher altitudes, the pressure is lower. It's not a pressure gage like the type you mount in the dash. That style has equal pressure on both sides and will read zero until pressure or a vacuum is applied to the port.

To use a MAP sensor in a data logger, you need to see what pressure it's reading with the engine off then let it record it's data. You then need to subtract the readings from the original pressure to see how much vacuum or pressure was created.

A 3 BAR sensor needs a different calibration than a 1 BAR sensor. All transducers work off a 0-5v (0.5-4.5v) reference but they're not all calibrated the same. You can do a google search to find the voltage reference for a 3 Bar GM MAP sensor.
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