JAFO1994

The MAP is a sensor I don't hear much about and the only one I really don't know what effects it has on engine performance. Could somebody enlighten me on function and what info it sends to the PCM. I believe it regulates intake pressure's. What are signs of it being bad or or common problems if any of it? I was going to remove it and clean it this weekend. It's about the only sensor I haven't replaced. Thanks

n2ceptor

Manifold Absolute Pressure sensor (MAP)--- Monitors the intake manifold pressure changes resulting from changes in engine load and speed, and converts the info into a voltage output for the ECM/PCM to control fuel delivery and ignition timing.....

Scanning codes are 33 or 34....


I had a rough idle and a small miss from 900-2000 RPMs... I changed out the MAP and it cured the prob, even though it wasnt throwing a code....

93Z Will

Blue96z28

TTT

i would also like to know the functions of this sensor more in detail and any stories people may have about problems/cures with the sensor.......i've been getting bad gas mlg lately, could this be the culpruit?

shoebox

n2ceptor described it right out of the book. Simply, it is a vacuum sensor. It does not control anything. Gas mileage and performance will be affected by a bad one.

Injuneer

But the MAP sensor affects key items like fuel and timing. The speed-density setup (93) requires it to calculate the density of the incoming air, then to look up volumetric efficiency and calcualte air mass flow. Then it adds the fuel to match the air.

In the mass-air 94 and up cars, it isn't used that way.... air mass flow is measured directly by the MAF sensor.

But timing is controlled almost totally by MAP..... the timing table is a grid, with RPM on one axis and MAP on the other.... MAP is treated as a measure of "engine load".... higher the MAP, the higher load the engine is under.

MAP is also used to define which long term fuel correction "cell" should be used for the fuel calculations... again a grid with RPM on one axis and MAP on the other.

MAP stands for "manifold absolute pressure" and can be thought of as the "opposite" of manifold vacuum. A "total" vacuum would be 30"Hg (at sea level). The corresponding MAP would be "0". Typical idle vacuum with a stock cam is 20"Hg. Corresponding MAP would be 10"Hg (or 30-35kPa). When the throttle is wide open, manifold vacuum drops to near "0". Corresponding MAP would be 29-30"Hg (100-105kPa).

When you turn on the key, before the engine starts to crank, the PCM looks at the MAP sensor and reads the barometric pressure, and saves it. If you have a scan and you want to convert the MAP readings to vacuum, you subtract....

BAR - MAP = vacuum.

Just remember to keep the "units" consistant.... the English system uses "inches of mercury" ("Hg) and the metric system uses kiloPascals (kPa).

The MAP sensor is extremely reliable and seldom fails. It is basically a "strain gage", where the thin metal diaphragm "stretches" and contracts in response to the manifold pressure, and the system measures the changes in resistance.

shoebox

What I meant by not controlling anything was, that it does not exert a physical change to something, like say the IAC. I was trying to show to the original poster that it did not "regulate intake pressure", as he put it. It is only a sensor. Obviously, the pcm uses all the sensors to make calculations to "control" the engine.



Fred always has the in depth explanation.

Blue96z28

thanks guys for your excellent responses