Fuel Check valve / 0.0 bar / faulty ECU pressure sensor

Henry A Harper III hah at alumni.rice.edu
Mon Jun 3 13:04:24 EDT 2002

I would suspect an electrical anomaly with the display unit long before an
actual intermittent significant *increase* in vacuum (decrease in manifold
pressure). A "vacuum leak" lets air *in* to the area under (partial) vacuum
thereby increasing the manifold pressure if anything. Your display would
read higher if there were a leak - up to 1.0bar @ sea level, no vacuum at
all, atmospheric pressure in the intake manifold, when the throttle plate
is wide open (for a non-pressurized/non-turbo engine, your positive
manifold pressure/smileage may vary with a turbo engine) because that is a
giant vacuum leak. The display would only read lower if there were a
"normal" leak that was sometimes sealing to pull a harder vacuum. That
seems unlikely since most people's cars show 0.3bar under deceleration.

Henry Harper
http://www.henry-harper.com  hah at alumni.rice.edu
1991 200 quattro, 116k, dash display showed ~2 mpg increase after cleaning
out air filter @oil change
1988 GTI 16v, 227k, wonder when that a/c compressor seal kit is going to

On Monday, June 03, 2002 11:26 AM, SuffolkD at aol.com [SMTP:SuffolkD at aol.com]
> --
> [ Picked text/plain from multipart/alternative ]
> LISTERS & Mihnea:
> Thanks for the reply.  The 0.0 and 0.1 happened while engine running,
> driving, during lift throttle while going down hill in NJ.  Original post
> April 7 & 8 2002.  (not in Archives under my e-mail or 0.0 bar)
> That's where I thought the fuel injector seals leaking allowed air to get
> sucked in to the vaccuum area where the vaccuum guage displays 0.0 and
> numbers in bar on the dash.  My guess is that while fuel injectors go
> directly into the cylinder for combustion, but when the valves are open
> the intake stroke could this "leak source" cause the vaccuum area in the
> manifold to be affected?..... Showing a 0.0 or 0.1 under lift
> that's a wild guess.
> You say check fuel pump check valve?
> -Scott in BOSTON curious as hell..............................
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