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flosho · Posted: Tue Sep 12, 2006 7:35 am Post subject: Lean Air/Fuel Ratio

I don't have a wideband yet, but I think my MR Gauge is helpful for looking at WOT conditions..

I did some testing, and on full throttle pulls my A/F gauge goes right on the lean/stoich line.. its not in the lean range, but its at the bottom of the stoich range, about *15:1 if I had to say.

That seems to be on the lean side, especially for making power safely. Now I'm running 12 PSI with an a/w intercooler setup, I also have a warm air intake and got rid of the air box.

When I'm idling it goes up to stoich and when I'm just cruising on the highway or in town it stays on the bottom side of the stoich. Could I have a partially clogged injector or what? Maybe i'll pick up a bottle of injector cleaner.

*15:1 is my estimate until I find my sheet that came with the gauge to tell me what incrament is..
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Tigger937 · Posted: Tue Sep 12, 2006 1:01 pm Post subject:

What do your plugs look like?

How does it run WOT, especially near redline............still pulling strong? Any backfiring in the exhaust between shifts?
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1981 931 (Concours)
1982 931 (Daily Driver)

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macBdog · Posted: Tue Sep 12, 2006 1:19 pm Post subject:

flosho · Posted: Tue Sep 12, 2006 2:50 pm Post subject:

leadfoot · Posted: Tue Sep 12, 2006 6:50 pm Post subject:

I would really recommend richening up your mixture, at WOT you should be near 12.5... WOT at 15 will kill your motor... for cruise this would be Ok.
I'm not sure how the turbo adjusts for O2, as far as I was aware the narrow band can only adjust minutely...
You could however use a WUR from an audi turbo and run the vaccum line to the manifold, this will lower the control pressure and richen the mixture during boost IIRC.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Smoothie · Posted: Tue Sep 12, 2006 11:16 pm Post subject:

leadfoot · Posted: Tue Sep 12, 2006 11:35 pm Post subject:

not working then is it?? maybye system pressure needs to be tested or shimmed up a little...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

flosho · Posted: Wed Sep 13, 2006 3:41 am Post subject:

Smoothie · Posted: Wed Sep 13, 2006 10:47 am Post subject:

This <click> shows the 931 WUR as item "F". The vacuum/boost line is shown coming off the right side and it connects to the side of the throttle body. That same vacuum/boost source leads to several other components as you can see. There is no adjustment for the enrichment function, but it can be tested. You'd need a CIS fuel pressure tester, an air compressor and a way to limit the air compressors' output to approx 10psi. You'd simply watch for a drop in control pressure when pressure is applied through the WUR's vacuum/boost line.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Tigger937 · Posted: Wed Sep 13, 2006 12:16 pm Post subject:

leadfoot · Posted: Wed Sep 13, 2006 12:18 pm Post subject:

You might have a vaccum leak at the WUR connection...
From what I understand about CIS mixture adjustment there are really only a couple of options...
First there is system pressure which you can shim up to 80lb via the pressure regulator on the side of the fuel dissy, this richens up the mixture overall in relation to how much pressure above control pressure is being run. Reports from 928 boards and books I've read say that there is not much point going higher than this and safety of the lines burtsing beyond 90lb is an issue.
Secondly, lowering control pressure by using a boost/vac variety such as you have... there is a way to adjust it further but it can result in leaking injectors if the difference is too great. You would need to verify this at cold pressure when the difference is the greatest.
http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm
Thirdly the allen key adjustment on the top of the fuel dissy, this however is reported to only adjust the idle mixture, therfore it would be possible by adjusting the other two methods above and using the third to negotiate off idle enrichment and to a certain degree under boost.
The next steps involve using a 928 fuel distributor and joining lines or using a pressure switch and wiring in another CSV.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Lizard · Posted: Wed Sep 13, 2006 1:02 pm Post subject:

i just want to confirm on this, but you dont have the AFM hooked up to the same O2 sensor that the lambda system is running off of do you?

as you can only hook up EITHER the AFM, OR the lambda off of the unit, but not both
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3 928s,

flosho · Posted: Wed Sep 13, 2006 1:23 pm Post subject:

Its hooked up to both, lambda and afm. So would being hooked into both matter, as in misreading on the gauge, or causing the mixture to go lean because the lambda isn't getting full voltage?
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flosho · Posted: Wed Sep 13, 2006 1:27 pm Post subject:

Min · Posted: Wed Sep 13, 2006 2:33 pm Post subject:

I don't know if you've mentioned it or not, but if this is a narrow band sensor, ignore it, narrow bands are useless for making fine adjustments in the tune of your car. If its a wideband, hook up a meter that can show you the proper numbers for your air fuel mixture so you know what you need to do. Not that you can do much with cis.

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.