Can some give me a detail explanation of the function of the MAP sensor?


How with the car react when it is not functioning correctly

Thanks

 

Jim:

It's the key sensor in selecting the operating points on the fuel and timing maps. The sensor measures the "manifold absolute pressure". MAP = the operating air pressure in the intake manifold, referenced to a perfect vacuum. If there is no air flow in the system MAP = the pressure of the surrounding atmosphere... or "barometric pressure" (BAR). At sea level, barometric pressure is typically 29.9"Hg or 103kPa. When you start the engine, you develop a vacuum in the intake.... at idle with a stock cam, you will see MAP = about 9.5"Hg (33kPa). As you open the throttle, there is less pressure lost in the throttle blades, and MAP starts to rise, approaching BAR at WOT. If you want to figure the manifold vacuum, it = BAR - MAP. 29.9 - 9.5 = 20.4"Hg vacuum.

In a speed-density system, the MAP is (one of the factors) used to calculate the mass of air entering the engine, so the PCM can add the required amount of fuel. In a mass-air system, it is not used for this purpose. What it is used for in both systems is as a measure of "engine load"..... the PCM interprets high MAP values as high engine load. It uses MAP (along with RPM) to determine which long-term fuel correction cell to use. It uses MAP (along with RPM) to select the timing advance. It uses MAP to determine how much to richen the mixture when it sees the throttle opening.

So.... if your MAP sensor if FUBAR, the engine will be trying to fuel for the incorrect conditions.... But, there are codes that will be set if the readings are outside of reality..... and the PCM will default to other sensors and fixed values. In any case, the engine isn't going to run like it should. With a blower, things get even more confused..... because now the MAP sensor is seeing the effects of boost. MAP sensors seem extremely resiliant, and seldom fail. The connectors will age and crumble though.... leading to wire contact problems.

 

Thanks Fred,
When you provide a detailed answer (to even a basic question), you help a lot of us to further clarify our own understanding of the subject.

Bob Bishop

 

Hi Fred,
Thanks for your explanation. The reason why I posted this up is because I am experiencing problems getting the car to idle correctly... After I sucking in all that water about two weeks ago. I have gone through and check everything including removing the throttle body and cleaning out the IAC sensor. Even after checking everything I am still getting a funky idle and it will stall out sometimes. According to the scanner I am running really rich but strange enough It seems to be running allot better on the top end of the rpm spectrum (am not showing any more knock retard) . (I am showing about 969 on the o2's where before it was running around 880-900) so I am not sure what's going on. Here are the codes I am showing … remember I no longer have the EGR, air pump or cats on the car so I am pretty sure some of the codes will show that. Can you tell me what these codes mean?

Thanks Jim


PO100
PO103
PO122
PO335
PO336
PO400
PO420
P1121
P1122
P1641
P1642

also my block learns were around 128

 

AutoTap has a code lookup site:

AUTOTAP OBD-II CODE LOOKUP

You need to pick "GM" on the top field, and then enter the FULL code in the lower field.... e.g. P 0 4 0 0.

PO100 = MAF insufficient activity
PO103 = MAF high frequency
PO122 = TPS volts low
PO335 = CKP sensor circuit
PO336 = CKP sensor perfromance
PO400 = EGR
PO420 = Bank 1 cat efficiency
P1121 = TPS intermittent high volts
P1122 = TPS intermittent low volts
P1641 = Fan relay #1
P1642 = Fan relay #2

Sounds like you have a major wiring problem, blown fuse, water in a lot of the sensors, or some combo of these. The MAP sensor seems to be the only one that is OK.....

 

Hi Fred,
Yes i know i have allot of codes but some of them are due to the modifications of the car

PO100 = MAF insufficient activity
PO103 = MAF high frequency
PO122 = TPS volts low
PO335 = CKP sensor circuit
PO336 = CKP sensor perfromance
P1121 = TPS intermittent high volts
P1122 = TPS intermittent low volts


Codes P1641 = Fan relay #1 & P1642 = Fan relay #2 , I tapped intot the line to override the fans (for better cooling ) when i turn them on manulally it casues this code.

But for the other codes like po100 and po103 would the erratic idle cause this type of problem ?

I have gone through everything with a fine tooth comb but i am not sure what direction to go.

Also What is the CKP sensor.

The one thing that really bogglesw my mind is that the car would run fine the all of a sudden the car will not want to idle run rich etc then it would run fine again it seem like it can't make up it's mind

 

maldo, did you ever determine what the problem was with your car? I am having a very similar issue with mine. Getting these codes..

PO100 = MAF insufficient activity
PO122 = TPS volts low
P1121 = TPS intermittent high volts
P1122 = TPS intermittent low volts

 

He hasn't posted in about 1.5 years.

 

that explanation was great, it helped me to understand the mas sensor

Here a late tnx to you!