Re: RE: belly pan gasket

From: Shane Moseley (smoseley@ix.netcom.com)
Date: Sat Mar 03 2001 - 12:24:29 EST


bernd@texas.net wrote:

> Vacuum leak.
>
> > Bernd,
> > Ok, you have to explain this one to me. If the pan gasket is leaking, the
> > only effect is in the crankcase recirculation. The airway from the TB,
> > through the intake and heads, into the cylinders has not been compromised.
> > Everything is metering normally. How can a lean condition occur?

Anyone with an A/F gauge (it really don't apply to everyone else because they are
guessing) - do this simple test: While warm and idling (gauge oscillating) pull
off one of your main TB vacuums and leave it open (massive vacuum leak). Watch
the gauge - what happens? You get a very temporary lean condition but shortly
thereafter - the PCM compensates by pumping more fuel - then the PCM realizes this
is now a higher rpm than requested (idle) so it adjusts the IAC by closing that
orifice (IAC is simply a controlled air bleed or in other words: a controlled
vacuum leak) until the desired/scheduled rpm is reached. Guess what the A/F gauge
is doing now? Oscillating around Stoich (14.7) as if a normal situation (albeit
pretty jumpy due to the lack of a more precision "control" orifice. If the vacuum
leak is so big that the IAC plunger closes completely before the desired/scheduled
rpm is reached, a MIL is set.

Think about it.

Latr,

Shane

--
'96 IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/MPComp/HookerSuperComps/CompTAs
'96 IndyRam-HerIndy-numbered(#142)"Track Truck"
'74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle
'68 Black Corvette Convertible 427 (For Sale)



This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:59:55 EDT