[Shotimes] Why does the CE light go on if the gas cap isn't tight on OBD II cars?

[Dave Kegel]

Here in IL they still pressure test the gas cap.  In fact, the cap on our
'98 Sable did not pass this past summer.  I had to go buy a new one in order
to pass emissions.  Never got a check engine light though.  According to the
emissions place, the Ford gas caps seem to fail quite regularly.

Dave Kegel
----- Original Message -----
From: "Jim and Debbie Leyden" <jndleyden@mindspring.com>
To: "Paul L Fisher" <sho@paul-fisher.com>; "SHOtimes"
<shotimes@autox.team.net>; "V8 SHO" <v8sho@v8sho.com>
Sent: January 29, 2003 2:42 PM
Subject: Re: [Shotimes] Why does the CE light go on if the gas cap isn't
tight on OBD II cars?


> I'll give it a shot.
> I think (and I could be wrong) that the evaporative emission control puts
a
> slight negative pressure in the fuel tank in an effort to caputure the
> vapors and recover them.
> The OBDII cars have more sensors on them than you can even imagine.  When
> you went in for an emissions inspection they used to remove your gas cap
and
> test the cap to see if it were working properly.  Since (at least here in
> GA) cars with OBDII supposedly know if your car is working right, all they
> have to do is plug into your cars OBDII port and the car will tell the
> examiner if it will pass.  So there must be some sort of pressure
transducer
> on the fuel tank to see what is going on.
>
> Jim
> '93 MTX