A/F ratios under varying conditions

[Jim Green]

--- Brady Moffatt <bradym at sympatico.ca> wrote:
> Hi All,
>
> Trying to troubleshoot the stumble under load/boost
> on my 83 UrQ. The car
> has a Lehmann ECU and SQ WG spring and diaphragm
> along with a nice ricey
> blow-off valve. I hate to admit it, but I'm getting
> addicted to its
> pssssshhhhttt sound. The car stumbles under load as
> of 4K in 4th and 3200 or
> so in 5th.
>
> Martin Pajak wisely suggested I get an A/F meter so
> I could get an idea if I
> was about to blow up my engine. I bought an APEXi
> Turbo Timer that also
> displays A/F ratio, O2 sensor (which is new and
> cycles beautifully) voltage,
> and battery voltage. Well, here's what it shows: At
> almost all times, the AF
> ratio is 14.5:1  + or - 0.5.  The only time it goes
> down below 14 is on a
> shift when the BOV opens and it drops to 12.5 at the
> lowest. Under boost at
> light to mid throttle up a small hill in 5th today,
> I saw the ratio creep up
> to 17. That scared me. If I floor it, my ratio may
> go down from 14.5 to
> 14.2, but not to 12 which is where max power is.
>
> I'm a bit worried. Combine that problem with a hard
> cold start (warm and hot
> starts are fine), and I'm leaning towards fuel
> pressure ills.
>
> What are the normal AF ratios that these cars
> perform in? Am I running way
> lean?

Hey Brady,

It sounds like you may be running lean on boost, but
it's hard to tell.  With a Narrow Band O2 sensor like
you have, it's hard to tell where exactly you are
unless you're right around 14.7 which is stoich.  So
your 14.5 at cruising sounds good.  The fact that the
Apexi is estimating where you are is scarry.  With NB
O2 sensors, I prefer a simple LED readout that
indicates rich, lean, or stoich.  Then you don't get a
false sense of security, and start looking at other
things like plug color, EGT's and the general sound of
the engine for tunning.

Does it stumble at WOT or part throttle?  How much
boost are you running?  If it's under part throttle,
maybe you need to adjust your WOT switch to engage
earlier, if you have one?

HTH

=====
Jim Green
'89 90tq
http://www.geocities.com/jeg1976/car_home.html

__________________________________
Do you Yahoo!?
The New Yahoo! Search - Faster. Easier. Bingo.
http://search.yahoo.com