Flucuating MAP at WOT
05-25-2007, 01:51 PM
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I looked at a log from my 1999 Z28 on the dyno yesterday. I saw MAP readings flucuate from 95-101 kPa. The stability of the MAP sensor seemed to get worse the higher the engine rev'd.
05-25-2007, 01:56 PM
#5
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There are a couple of possibilities. Electrical, some kind of
induced noise on the MAP sensor output or bled through
from the supply). Or maybe there is some motor issue like a
sparse misfire, changing cylinder filling, or a valvetrain thing
like resonance.
My MAP readings are pretty stable historically because I was
not "challenging" the intake tract by motor pumping. Have a
good cam and exhaust setup and you draw down harder and
any irregularity is then visible. Wimp cam, always see max or
max less a point.
In reality the manifold pressure is very not-stable and a big
cam makes bigger pulses. Depending on how the sensor filters
the pressure transducer output, and how the PCM samples
it, you can catch a crest or valley and the phasing between
sample and actual can give the illusion of stability where none
really exists.
induced noise on the MAP sensor output or bled through
from the supply). Or maybe there is some motor issue like a
sparse misfire, changing cylinder filling, or a valvetrain thing
like resonance.
My MAP readings are pretty stable historically because I was
not "challenging" the intake tract by motor pumping. Have a
good cam and exhaust setup and you draw down harder and
any irregularity is then visible. Wimp cam, always see max or
max less a point.
In reality the manifold pressure is very not-stable and a big
cam makes bigger pulses. Depending on how the sensor filters
the pressure transducer output, and how the PCM samples
it, you can catch a crest or valley and the phasing between
sample and actual can give the illusion of stability where none
really exists.