MAP (Manifold Absolute Pressure) Sensor

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Old 22 Jan 2005, 09:00 pm   #1 (permalink)
BillRaft
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Default MAP (Manifold Absolute Pressure) Sensor

1995 4 cylinder Camry, Can anyone out there tell me what voltage reading
one should get from the MAP Sensor when drving through a range of RPM? The
book says that there is a 5 volt input and with 25hg vacuum you should get
5 to 1.5 volts reading on the PIM side of the connector plug. Thanks

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Old 23 Jan 2005, 07:51 am   #2 (permalink)
Daniel
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Default Re: 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:
4:.4, 8:.8, 12:1.2, 16:1.6, 16:1.6, 20:2.0

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Old 23 Jan 2005, 08:11 pm   #3 (permalink)
BillRaft
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Default Re: MAP (Manifold Absolute Pressure) Sensor

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.



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Old 24 Jan 2005, 07:58 am   #4 (permalink)
Daniel
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Default Re: MAP (Manifold Absolute Pressure) Sensor

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.

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Old 24 Jan 2005, 01:18 pm   #5 (permalink)
BillRaft
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Default Re: MAP (Manifold Absolute Pressure) Sensor

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
087 volts)with the ignition key to on. When I started the car, the
voltage went up past .1 volts. After it warmed up it registed fluctuations
between .1 & .9. SOme instances it registered below .1.

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