MAP (Manifold Absolute Pressure) Sensor

Hi Bill,

Seems like you're looking at an area that is unlikely to solve your problem. If the MAP sensor tests bad, please report back, will be the first one mentioned. Just a simple pressure transducer at the end of a long vacuum line. Little chance for contamination or malfunction. The hot wire sensors in the intake stream (V-6 model) are a different matter - can be contaminated by oil residue from foam aftermarket air filters for example. Basically, you're looking for a linear progression from the MAP sensor. The FSM graph is a straight line beginning at 4" mercury and .4 volts and rising to 2 volts at 20" mercury. The factory manual recommends testing in five increments and lists the following values rounded to the nearest inch Hg. and +/- .1 volt:

Thanks for the info.... After checking further, I found the oxygen sensor voltage is all over the place when cold and when I rev the engine and stabilize the RPM, the voltage is very very erratic....I think that the O2 sensor is the probable cause.

O2 sensor doesn't emit voltage until hot - something like 600 deg. F. IIRC. Connect a voltmeter from the OX1 underhood data port to ground with a voltmeter set on the lowest scale, and count number of swings past zero in ten seconds at 2500 rpm to confirm condition. If you're going to be checking this kind of stuff, get the factory service manual and just follow their step by step procedures. That way you know you're checking things correctly. Plus you'll find many helpful pointers when doing routine maintenance and repair. Small items that are important and otherwise overlooked. As far as "erratic" O2 sensor readings - when it is working correctly, the voltage will swing past zero in alternate directions - the more often the better. That means oxygen is being monitored and adjusted by the ECM. If the O2 sensor is coated with carbon, it could become "lazy"

- perhaps less "erratic" in your terminology - for O2 sensors frequent fluctuations are a good thing demonstrating proper sensitivity to oxygen concentrations. Here's another idea. Some of the sensors you're checking are quite sensitive. If you connect an ohm meter to one that should not be checked in that manner, you can instantly damage an otherwise good component.

THanks....I'll get the Factory Service Manual for future work. I checked the sensor in the way you stated. I checked the engine early this morning after the car sat all night. I had a voltage reading (minimal as it was