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Join Date: Oct 2006
Location: Chas, SC
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AFR's (Idle and Cruise)

I know there is a similar thread, but I did not want to hijack....

Regarding running O2 Disconnected, Cruise AFR's low 13's.

My Warm and Cold pressures (Leask WUR) are spot on spec (lower end, but in spec). I have adjusted my AFR's at idle from 12 - 13.5, and my steady cruise AFR's are still rich, at low 13's. The cruise AFR's are NOT effected by changing the CO at idle, as I have been experimenting with this. My car idles much better at 12.5 than 13. 5, so I have it set at 12.5. Cruise AFR's are still low 13's. I do have a freq valve, and running O2 disconnected.

My vacuum advance and retard both work on the dist.

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1986 930
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Old 03-31-2013, 05:14 PM
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If you are running the warm CP at the low end of the spec then it will tend to be rich on cruise. You might then be running the idle adjustment screw at the full lean end of its travel to get idle back to a lean enuff range. Basically one control set at the minimum and the other set at max leaves you no wiggle room of adjustment left.
Maybe try increasing warm CP and then richening up the idle control screw to get back to 12.5 to 1 idle and see where the cruise is then.

I dont know much how that freq control valve effects things as i have no esperience with it in my 79 930.

Good luck,
Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-01-2013, 06:15 AM
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Quote:
Originally Posted by fredmeister View Post
If you are running the warm CP at the low end of the spec then it will tend to be rich on cruise. You might then be running the idle adjustment screw at the full lean end of its travel to get idle back to a lean enuff range. Basically one control set at the minimum and the other set at max leaves you no wiggle room of adjustment left.
Maybe try increasing warm CP and then richening up the idle control screw to get back to 12.5 to 1 idle and see where the cruise is then.

I dont know much how that freq control valve effects things as i have no esperience with it in my 79 930.

Good luck,
Fred
Good advice. FWIW, when the lambda system is in open loop (unplugged sensor) the frequency valve will default to a fixed duty cycle, if I recall it's 50% but would have to look it up in the book. So the freq valve then becomes a constant that you tune around.
The other unstated possibility is that the AFR gauge isn't properly calibrated and is reading richer than it really is, since the car seems to idle so much better at 12.5...which is really pretty rich for idle. But each car seems to have it's own sweet spot.

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Old 04-01-2013, 07:25 AM
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