MAP Diagnosis

[FTA1995]

I think my MAP is toast.

Its giving me a 96 kPa read-out, key on engine off throttle open with a 29.89" outside(from the high school 2 miles away).

96.47kPa=13.99 PSI=28.49" HG

The BAR reading of the MAP is off by more than 1 inch of mercury, enough to goof the timing a little, etc.

Thoughts?

[SeanC]

I was getting kind of weird readings with my MAP recently, but nothing like yours. At idle, your suppose to get somewhere around 9.4"Hg. If its a constant wrong reading, I would think that the sensor is bad. If it was more intermittent, I would look towards the wiring. How do the connections look on the sensor itself? How does the wiring harness plug look? Is it corroded?

Sorry I can't help that much buddy, but I figured I might as well try since I had a similar problem.

[FTA1995]

Where do you live? How far above sea level? these are important to ask yourself about this sensors data... I get a value of about 15-17 kPa, but i have a bigger cam than stock (and possibly a bad sensor). With a barometer of 30, you should see between 9-10 kPa on a mostly stock LT1. Yours is probably fine. you need to check it like I did, engine off, key on, see what the barometer is outside, record your sensor data and see how accurate it is. as long as your Idle MAP is less than or equal to 1/3 of the BAR, you shouldn't have a problem.
MY problem would be different, I can't relate my sensor output to the actual conditions of the atmosphere like it should.

[FTA1995]

To add more to it,
the pigtail to the plug is broke ant the lock, but ive got a good connection at the terminals.

[Injuneer]

At sea level, a stock LT1 will see 9.5-10.0"Hg at idle. That's about 20-20.5"Hg vacuum. You should be seeing something in the range of 30-35 kPa at idle. 17 kPa at idle will set the code for low voltage on the MAP (irrationally high vacuum). An LT4 HOT cam might produce closer to 50 kPa at idle.

The MAP sensor harness connector is well know for crumbling with age and making poor contact. Check for a full 5.0V reference at the connector as well.

[FTA1995]

Thanks I'll check it out.

[FTA1995]

checked everything and the connection is good, although I did break the clip lock some time ago, it plugs up solid and stays where it should.

Still getting the same off reading, anywhere from 1-1.5 inches of mercury off the actual pressure outside. on a 30.03" day it doesn't even hit 100 kilo pascals.... I'm pretty sure its the sensor, when they get old the little sealed vacuum or pressure constant chamber breaks open or leaks a little, rendering the MAP useless and inaccurate.