High vacuum.

Howling Mad

Active Member
Joined
Aug 23, 2010
My car normally runs about 18 in of vacuum but will driving today it dropped to 30 on the gauge, power logger showed 34. Any ideas?
 
Could it be the map sensor just lost power or ground? Cut / loose wire, plug, bad connection? Something like this?
 
On the page where you can load tunes and logs you can adjust the offsets of the map sensors aswell as anyother sensor hooked up . What sensor are you using ? I’m curious about the limits in vacuum of a stock style 3 bar . Because if it can read 3bar of Boost which I believe is 30ish does that mean it reads 30 hg of vacuum aswell ?
 
I doubt it. I've never taken apart a GM MAP, but there's no rule that says atmospheric has to be in the middle of the range. Then again 99% of GM cars that use a MAP sensor never see boost, so the highest they can read is just shy of atmospheric.

1 Bar is a little over 14PSI, so 3bars is 43.5 pounds of boost.

An inch is right at 1/2 a pound (that's why the FP only drops a few pounds when you reconnect the vac line at idle)
 
Sounds like you may have a 2 bar MAP with a 3 bar selection on PL?
Make sure the MAP selection is correct on the PL console, and go from there.
 
It's a 3 bar map, I was thinking maybe a voltage issue, it did it yesterday when the car was hot, but not since?
 
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