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Old 07-09-2009, 07:08 PM   #1
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Default intake manifold pressure

Can anyone tell me what I should be reading for "intake manifold pressure" at idle for NA 2002 3.8 as seen on a scanner ? I'm reading about 10" and that seems low.

Also, with key on, no start, my MAF is reading .2, .9 at start and idle.. don't know how significant that is (the non-zero value at no start condition)
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Old 07-09-2009, 08:03 PM   #2
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Sounds about right..

The .2 is technically the amount of heat it takes to keep the maf at the specified temp. That'* how it reads..it somehow tells how much power it takes to keep a wire at a constant temp. Could be normal.

Got any symptoms you are trying to diagnose or just checking things out with a scanner?
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Old 07-09-2009, 08:13 PM   #3
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The manifold pressure sounds about right. Because your NA you have a vacuum, not pressure. Subtract 14.7 for normal air pressure and you have the amount of vacuum.
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Old 07-10-2009, 08:31 AM   #4
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It'* the same for a supercharged car since we are talking idle. You have vacuum on both.
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Old 07-10-2009, 09:36 AM   #5
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broke this question away from the "another stall issue" thread since it was a quick and dirty.. I see the scale is reversed for vacuum from what I"m used to .. 30" was perfect vac.. with this 0" must be perfect vac, since it'* at 29.9" with key on no start.

Still following the path that leads to PCM replacement..
So far have eliminated (by swapping or replacing):
ICM, plugs, wires, crank sensor, cam sensor, coils,MAF,IAC,TPS,EGR.

about the only things left are O2 and pcm.. and since it happens on startup (cranks, fires up immediately, then quickly dies) the O2 shouldn't be in the loop yet. Was going down the contaminated gas route for a while there, but that seems remote, especially with all the ethanol in todays fuel, shouldn't have a water issue.

only have a couple hundred in it so far, about what I would expect to pay for a good class on electronic control systems for the 3.8 engine
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