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Do Manifold Pressure Sensors (MAP) go bad?

lazyxj

NAXJA Member #1310
Location
Los Angeles
Over the past 11 years, every sensor on my 2001 XJ has been changed with the exception of the manifold pressure sensor (MAP).
Can't remember ever seeing anyone posting about a MAP problem.
What symptoms would a bad MAP display?
Anyway of testing one?
 
You should be able to measure the DC voltage output. You can find a table that gives you outputs based upon pressure. Just disco the vacuum line, look up your altitude in the table and go for it.
 
What symptoms would a bad MAP display?
Anyway of testing one?

more often than not, the MAP fails when it no longer holds vacuum. It senses pressure (or vacuum) in the intake and uses what it sees to vary output back to the ECU. This, in turn, is used by the ECU to adjust fuel mixture to match engine demands and atmospheric pressure.

When the MAP looses it's ability to hold vacuum, it returns a false "low vacuum" reading to the ECU which results in a very rich mixture (black sooty exhaust) It will sometimes be masked at idle if the vacuum leak allows enough air to enter the intake, but the sooty tailpipe will give it away soon enough.

As stated previously, an output check at varying levels of vacuum will determine both it's ability to hold vacuum and it's ability to return the correct signal.
 
You should be able to measure the DC voltage output. You can find a table that gives you outputs based upon pressure. Just disco the vacuum line, look up your altitude in the table and go for it.
Thanks for the response and suggestion to find a table.
Found the following thread and chart.
http://www.naxja.org/forum/showthread.php?t=1085671&highlight=manifold+absolute+pressure

http://www.fastfieros.com/tech/map_sensors_and_how_they_work.htm

While setting up a box of spares, I'm making a list of showing each sensor and its correct voltage or resistance measurements. It should help speed trailside diagnostics and repairs. The MAP is the only sensor I have not dealt with before.
Guess I need an altimeter (or a barometric gauge) and a voltmeter to check the MAP sensor.
 
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