Garrett Lim@GIAC

Hi,

edited by Garrett (9/15/04) 14:59

I would like to clarify a couple of points raised in recent posts concerning air fuel ratios of our code on a wide band sensor (As background information: We use a Motec A/F [air fuel] meter integrated into our 4WD dyno, many Nascar guys prefer this unit.).

A recent post, in this forum, showed that our, off-the-shelf, 91-octane 2004 1.8T B6 A4 chip was dynoed on 100-octane fuel but resulted in some confusion over the A/F plots. Those A/F plots look right for race fuel. Our S chip runs ~ 20-22 ms of injector on time, with stock injectors on 91-octane (on most cars this program runs in the high 12's for A/F in front of the CAT without misfire). We have logged data from the dynoed car and it ran a similar ~20-23 ms on 91-octane code with 100-octane (and this does not leave much more room, the only other option for more fuel with like injectors is adding fuel pressure or tweaking injector timing in the code, which does very little to fuel delivery). The minor problem is that the higher octane increases the timing and causes it to run leaner (but remember 100 octane ensures safety even when this is the case, on the 0.7 bar-> 1 bar -> 0.7 bar S chip, with the very low flow of the small K03). This is why we do not offer a B6 race fuel Flashloader switching option for stock injectors. We offer race gas programming only for the BETA 380 cc injectors. The tested car had our flashloader - 4 chip option. Stock/91/Valet/kill 518AK code.

When the car recently was tested and ran more boost it "appeared" to run richer than our 91 octane S chip (as measured through a wide band O2). It was likely misfiring (if the fuel was burning on the exhaust it would appear richer as the O2 drops.). Remember A/F is calculated from O2 content in the exhaust, and O2 content decreases (edited) when there is more fuel. The confusion arises when misfire is present because tuning will appear rich when it is not. It can mimic a rich mixture as the unburned fuel passes and burns (edited). If this is happening, the tuner must add more fuel, correct the cause of the misfire, or use the narrow band sensor (like the rear O2 sensor) as it is less sensitive to misfire or watch the EGT'S (edited).

To exibit this: one test is to cut injector pulse in 1/2 on a turbo car (assuming you have VERY good octane) and keep the boost the same. The wide band will display 12:1->11:1->10:1 as it misfires. You can see the miss (fuel coming out of the tailpipe).. And it will read as very rich, even though the car is lean.

The car tested did have misfire codes prior to the installation of GIAC software and I was told it did have a misfiring at F/T on the dyno in the mid range on the (the local tuned "custom code") code running 1.4-1.5 bar. Ours did not missfire at 1 bar. The car was using race fuel and it is only a K03: So the motor should be fine with either code on the dyno. Even if it was 17:1, it should not be a safety issue on 100-octane if there isn't too much timing. FYI - Max power is always 13:1-13:8 (on the Motec) at F/T if you have the octane and all else is equal (boost, timing, etc.).

This 91-octane B6 software version 2.8 from GIAC has not changed (and has been tested to countless times because of old controversies surrounding the programmability of this motor) for ~ 2.5 years and has not caused a single issue. It is extremely reliable, even on 91-octane in Az, heat (120deg. On the roads.).

Regardless, most software for stock turboed B6 A4 cars is very safe. It is difficult to cause damage since the chip has inherent routines that force the E-gas pedal closed when conditions are suboptimal.

If you have any questions please email me.

Regards,
Garrett Lim
President
GIAC

Imolavirus@BuehnEngineering

thanks for the explanation : )

Garrett Lim@GIAC

you're welcome...

RocketBoy

What is the connection between timing and A/F that causes increased timing to lead to leaner A/F?

Todeshandler

Thanks for clearing that up Garrett.

dscottjr

a/f ratio.

edit -- that is holding the injector ms constant, in case that wasn't clear in garret's post

Mark P

and if this is an issue, why tune the car to have the timing try to go that high

dscottjr

Great post. It's always a pleasure reading your posts.

Garrett Lim@GIAC

Exactly.. well said.

That B6 was running in the mid 13s in the low RPM on RACE fuel with 1 bar and that is hardly dangerous. Timing always goes up slightly with race fuel.

Garrett

DarinS4Turbo

During a misfire, all that unburned oxygen reaches the oxygen sensor and so it reads artificially lean. (the O2 sensor knows nothing of unburned fuel). Is there somehow another factor here causing misfires to read rich instead?