Question Adjusting AFR's
10-05-2006, 01:37 PM
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Question Adjusting AFR's
At cold start my AFR is 19.5 and then drops to 13.5-14 at warm idle. At 5000-6000 RPM @ .8 bar I'm seeing AFR's of 11.2-11.8. The question is where do I start adjusting ? I'd need to add fuel at cold start and take some fuel out at full throttle. I have the B. Leask adjustable WUR which is set at 2.5 bar cold, 3.75 bar warm and 2.8 bar enrichment in addtion the the IA fuel head mod. The AFR's are really not that far off on warm and enrichment....guess not much adjustment needed here. So should I set the CO first and then adjust the WUR to richen up the cold or what ?
10-05-2006, 03:19 PM
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Hi Jim,
It sounds like your car is running well with the exception of a lean cold start. I would recommend setting your warm idle %CO where you want it first. Do this with the mixture screw on the air-flow meter. With the IA fuel head, it is possible to tune the idle to 14.5 AFR (0.2 %CO) and still have enough fuel under boost at redline. Then you can adjust the cold control pressure to richen cold starts. For cold starts, an AFR of around 11 to 12.5 (9.4 to 5.3 %CO) should do the trick depending upon your climate. The mixture will immediately begin leaning out from there as the heating element inside the WUR warms up.
It is pretty easy to adjust the cold control pressure and the WUR does not need to be removed from the car to do so. Here's an excerpt from page 2 of the documentation that describes the procedure:
To lower the cold control pressure - Loosen the 10mm hex nut at least one half to one full turn. Use a hammer and soft drift to tap the stud down into the body of the WUR. Keep watching the CIS fuel gauge while striking the drift with the hammer. Stop when you achieve a fuel pressure slightly below the desired value. Performing this procedure might take a few tries as you do not want to strike the drift too hard, only hard enough to drop the fuel pressure slightly below the desired setting. You can then tighten (turn clockwise) the 10mm hex nut to bring the pressure up to the exact desired value.
You will want to make sure the car has cooled off for at least a couple of hours prior to checking the cold control pressure. Since your car seems to be so lean during cold starts, try a cold control pressure of around 2.0 bar. This also assumes that you have a CIS fuel gauge to test the pressures. If you do not, you can try doing it "by feel" and checking your results with the wideband O2. I will PM you with more info.
Cheers,
Brian Leask
It sounds like your car is running well with the exception of a lean cold start. I would recommend setting your warm idle %CO where you want it first. Do this with the mixture screw on the air-flow meter. With the IA fuel head, it is possible to tune the idle to 14.5 AFR (0.2 %CO) and still have enough fuel under boost at redline. Then you can adjust the cold control pressure to richen cold starts. For cold starts, an AFR of around 11 to 12.5 (9.4 to 5.3 %CO) should do the trick depending upon your climate. The mixture will immediately begin leaning out from there as the heating element inside the WUR warms up.
It is pretty easy to adjust the cold control pressure and the WUR does not need to be removed from the car to do so. Here's an excerpt from page 2 of the documentation that describes the procedure:
To lower the cold control pressure - Loosen the 10mm hex nut at least one half to one full turn. Use a hammer and soft drift to tap the stud down into the body of the WUR. Keep watching the CIS fuel gauge while striking the drift with the hammer. Stop when you achieve a fuel pressure slightly below the desired value. Performing this procedure might take a few tries as you do not want to strike the drift too hard, only hard enough to drop the fuel pressure slightly below the desired setting. You can then tighten (turn clockwise) the 10mm hex nut to bring the pressure up to the exact desired value.
You will want to make sure the car has cooled off for at least a couple of hours prior to checking the cold control pressure. Since your car seems to be so lean during cold starts, try a cold control pressure of around 2.0 bar. This also assumes that you have a CIS fuel gauge to test the pressures. If you do not, you can try doing it "by feel" and checking your results with the wideband O2. I will PM you with more info.
Cheers,
Brian Leask
10-05-2006, 05:47 PM
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Thanks Brian, thats the exact procedure I needed. Yes the car is running well with except to the lean cold start which as you say can be easly fixed. I'm looking for 14.5-14.7 warm and 12.2-12.5 at full boost and RPM. Having the adjustible WUR is the ticket 
