At 08:28 PM 5/21/01 -0400, you wrote:
>So that was your scan tool reading that. When I hook my scanner up, the
>MAP is only sensing 12" of vacuum. I got the 15" reading directly off the
>intake manifold. Could I have a bad MAP? Doug Myers
Hi, Doug
All the readings that I sent were from a scanner. The 2nd set was done on
the driveway just before emailing it.
I would personally test the sensor first. I see that Shane has sent a test
procedure (just a wee bit different from what I've seen but it looks good).
I'm assuming that you were taking a reading with a vacuum gauge from
the intake manifold. I've found that most vacuum gauges are not very
accurate but, regardless, a digital volt-ohm meter hooked onto the MAP
sensor is the more accurate way to measure the engine vacuum because
it is the input voltage signal that the PCM monitors.
I don't know if this is true with our type of setup but I've read that even a
scanner MAP readout can be tricky when using it as the sole diagnostic input.
Apparently, under some circumstances, some computers can substitute a
default figure (stored in its nonvolatile memory) for a MAP readout which will,
in turn, result in a false vacuum figure.
Bob
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