Rob O

When I had my car dyno'd I also had air/fuel logged and mine was all over the map; it never leveled off, experienced a number of spikes and just didn't look good in general.

Professional opinion says it should have leveled off around 11:1 and maintained that general ratio the duration of the pull. Mine graph looks like a volitale stock chart.

The tuner says it's most likely my chip (AMS). What can be done about this and what are the effects of inconsistent A/F mixture?

I'll scan and post the graphs when I get home tonight.

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VerrÜckt

How were your MAF readings?

DAP@EPL

Here's a chart of AFRs from a few S4s from the dyno day at XX Tuning back in January.
<img src="http://pictureposter.audiworld.com/6924/afr-comp.jpg">

You probably want the AFR to be in the 12s (or perhaps high 11s) when on boost. If the AFR is incorrect, it definitely will affect power... too rich will lose power and too lean will heat things up too much and cause detonation (which will affect power as well). Way too lean and you risk destroying the motor.

-Dave Pramanik

Mark P

should be interesting to see - wait to comment till then

Rob O

But it's a relatively new MAF that passed service inspection just a month ago.

wishbone

CHEATER!!! So Generally I don't really think there is much you can do. That's generally a function of the tuning and how your vehicle reacts to it. However, at WOT I agree with the "professional" opinion, it should stay rich from around 3500 onward. Also keep in mind that A/F ratio was out the back of the gas. You really need to VAG it from the O2 to really check it. It's not as good as a wide band, but I think it's better than some probe at the end of your tailpipe. If you have a leak or something else is going on in your exhaust I htink there are just too many other factors that could make that unreliable.

Rob O

I view my AFR as an issue relative to readings from others, which were much more consistent and "flat" up in the rev range. Kieth's H-box AMS was "all over the map" like mine, but I don't think Marc's exhibited the same sporadic readings on his AMS M-box. So I'm trying to discern if it's the AMS box in my, car or something greater, and the impact on performance and reliability with such spikey AFRs.

This post also reminds me that I forgot to scan my stinkin' dnyo graphs. :-/

wishbone

Leaks in the exhaust, variances in the CATs, different types of exhausts maybe? I dunno just a thought. Marc's graph wasn't all over the place, but it did appear to be somewhat lean from what I recall. You're right about Keiths though, it was very strange.

Maybe try matching what you got at dyno-comp with a VAG-COM run, wouldn't hurt?