A/F ratios under varying conditions

[Brady Moffatt]

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?

Cheers,
Brady Moffatt
Montreal, Quebec, Canada
83 UrQuattro with 52,000 miles
86 4ksq with 310,000km
86 4ksq parts car
72 Datsun 240Z with 180,000 miles
92 VW Golf with 200,000km FOR SALE
in middle stages of quattrosis accumulatus


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