[Shotimes] lost MPG due to fuel pump?

[Kevin & Cheryl Airth]

> Kevin,
> Thank you for an informative and well thought out response.  I would like
to
> add one small tidbit if I may.  I was told (by a certain SHO Guru) that
when
> the key is operated from the OFF position to the START position (as
opposed
> to from the ON position to the START position) that the PCM runs what I
will
> call the "START_SUBROUTINE".  The subroutine enriches the fuel mixture to
> allow a faster start.  It is the same basic idea as the choke on a
> carburetor engine.  I have tested this theory myself by trying both ways
> when the engine fails to start on the first try.  If you merely turn the
key
> to start again, the engine will more than likely still be difficult to
> start.  However, every time that I shut off the key and re-try to start
the
> car, it usually starts right up.  Furthermore, I was told by a VW mechanic
> that is the reason the VW's (the older ones anyway, I can't speak for the
> newer ones) had a mechanical lockout that required you to turn off the key
> before attempting to start the car again.
>
> Jim
> '93 MTX

Jim:
 I have not heard that! You are correct that EVERY time the PCM is powered
up it goes though a POST (Power On Self Test). I don't know what it all
checks but it strictly is just a PCM only test.

But your test has another reason why it works that way. When you turn the
key off and then on you get the 1 sec. of fuel pump running time. This
happens regardless of the fuel pressure or engine status. Now when you leave
the key on and start it again you have not primed the fuel system with this
1 second burst of fuel. So it should start quicker by turning the key fully
off and then on instead of just turning it from on to start again. This is
why when troubleshooting a hard to start condition always see if multiple
times of turning on the ignition before starting helps. If it starts
quick/better then it points to slow/weak fuel delivery problem.
.
.