map sensor

screamer69 · Post by **screamer69** » Mon May 15, 2006 3:07 pm

i dont no if theres anything wrong with my map sensor or not but with it plugged in i get 102 kpa before i even switch my engine on ??

the car runs ok and boosts as it should ive had to ajust the fueling a bit but onther than that its fine

im useing the rs autosports 4bar map sensor

i took mine out and replaced it with another one and i get the same reading

should i worrie about this or is there something wrong it vorks fine just an odd reading to start with but its a bit harder to setup due to boost gauge saying one thing and m/s saying another

evolotion · Post by **evolotion** » Mon May 15, 2006 3:33 pm

that sounds right too me, the boost gauge is measuring "gauge" pressure and the map sensor is measurign absolute pressure. i.e. there will always be a difference of ~100kpa between the two.

screamer69 · Post by **screamer69** » Mon May 15, 2006 3:37 pm

ok thanx

at full chat im running just under 10 psi boost and m/s is saying 165 kpa is that right then ???

i carnt get my head around kpa !!

thanx again

evolotion · Post by **evolotion** » Mon May 15, 2006 3:50 pm

well 65 kilopascal = 9.427 452 97 pound/square inch

so 165kpa = atmosphere+ approx 10psi.

if you do a quick search on google for a description of gauge(or gage if your american) and absolute pressures it should all become clear.

screamer69 · Post by **screamer69** » Mon May 15, 2006 3:52 pm

many thanx

after all that i think ive got it round my thick head !!

i can build a bloody engine and m/s unit but couldnt get my head around it

thanx again im on the right track now !!

evolotion · Post by **evolotion** » Mon May 15, 2006 3:53 pm

just found this snippet, explaisn it quite well

dont worry, i rmember covering it in uni and it took a while for everyone to click what was going on

Absolute pressure vs. gauge pressure

Pressure gauges can be further classified into those reading absolute pressure and those reading gauge pressure. Absolute gauges measure the pressure of a fluid referenced against a vacuum. Aneroid barometers and altimeters are good examples, and the Manifold Absolute Pressure (MAP) sensor used in the engine control systems of modern fuel-injected automobiles is another. Gauge-pressure gauges measure the pressure of a fluid referenced against ambient air pressure. The Bourdon tube gauge discussed above is an example. The displayed reading of such a gauge will vary as local atmospheric pressure changes. However, if the gauge is designed to read pressures of many atmospheres, the error between gauge pressure and absolute pressure is usually so small as to be negligible.

A differential pressure gauge is a special case of gauge-pressure measuring instrument, designed to display the difference in pressure between two points. A liquid-column manometer is one example of such a gauge. Such instruments have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator to watch two separate gauges and mentally determine the difference in readings.