Re: fuel economy theory

["Ian Overholt" <ioverholt@hotmail.com>]

How about this theory?  Your mixture was adjusted on the rich side to 
compensate for the vacuum leak.  Now that you've plugged the vacuum leak, 
you are running too rich and are getting poor mileage.  Do you see a lot of 
carbon on the back of your car?  Blackish smoke?  I would just take the car 
to a mechanic who can adjust the mixture while checking the CO.  If you 
continue to run too rich, your cat will not last very long.

Ian Overholt
'88 16v
'78 Champagne Edition


----Original Message Follows----
From: Oliver Seiler <oseiler@acm.org>

My theory is that the ECU thinks the engine is
running lean (dead oxygen sensor) so it tries to richen the mixture. With
the vacuum leaks, however, air flow through the air flow sensor would be
reduced, meaning that the extra fuel the ECU is trying to provide
(changing the duty cycle on the frequency valve) isn't actually getting to
the injectors, so it sort of balances itself out (in my case, the mileage
was around 19 MPG before I started mucking about). Plugging the vacuum
leaks increases air flow through the sensor, which increases the amount of
fuel to the injectors, which causes my mileage to get worse. I wonder if a
previous owner just started unplugging things until he passed emissions
tests...

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com


--
Email problems to: scirocco-l-probs@scirocco.org  To unsubscibe send
"unsubscribe scirocco-l" in the message to majordomo@scirocco.org