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Roger Hall's Avatar
 
Join Date: Dec 2001
Location: Cordova, TN
Posts: 1,222
Air Fuel Mixture Guage

As recomended I bought a Air fuel guage. What should it read. Mine fluctuates from lean to rich. Then when I accelerate it goes all the way lean. It catches up as the speed levels off and goes from rich to lean. When I let off the gas it goes slightly rich. I am sorting out some problems and I am sure this is not right, but I was wondering what the guage should read.
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Roger Hall

81 924 N/A

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.
Old 04-06-2003, 06:46 PM
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Roger, fluctuating from rich to lean under cruise conditions is normal and necessary for the catalytic converter to operate properly. When you accelerate, it should go to the rich side 700-900mv under full throttle. It sounds like you have a lean problem under accel but proper mixture/operation at cruise.
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Old 04-06-2003, 07:12 PM
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Thanks

I figured it should fluctuate since the O2 sensor is attempting to lean the mixture.

I have a problem with bad input to my frequency valve. Im pretty sure its a wireing issue. Maybe a bad TPS also.
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Roger Hall

81 924 N/A

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.
Old 04-06-2003, 07:20 PM
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Roger,
I just sold my 1982 924 and have a lot of expierence adjusting the CIS system.
What you are seing in called 'dithering' which is running 'closed loop' and the O2 signal is having the computer adjust the fuel mix back and forth. When full throttle, you should go rich. Make sure your full throttle switch on the throttle body is working.
There were 3 switches on mine, 2 at idle and 1 WFO. Do you know how to adjust the idle mixture??? This will effect fuel delivery across the board somewhat.
Heres a good place to go for more info

http://www.924.org/contents.htm
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Old 04-07-2003, 10:13 AM
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Thanks for the link. I spend alot of time at 924.ORG. Yes I know how to adjust the A/F mixture. Here are some of the things I have done:

New air filter, fuel filter, cold strart valve, WUR, injectors.
Swaped out used parts to rebuild fuel dist, and AMFU. Replaced ECU with used one. Rebuilt fuel dist with used parts from an AUDI 4000.
Cleaned all grounds and connections.
Three TPS switches all checked with continuity meeter ok. I never checked adjustment and voltage though.

Here is what I think:
Frequency valve fluctuates because of the dissimilar input check this post Sensor Question The signal to the freq valve is bad, and the A/F guage spends too much time in the lean range.

Next is either the wiring or adjustments on the TPS or the RPM module. I have another used RPM module I will install it after I check the wiring for continuity and voltage.


New fuel filter

I belive there is more than one problem
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Roger Hall

81 924 N/A

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

Last edited by Roger Hall; 04-07-2003 at 01:52 PM..
Old 04-07-2003, 01:13 PM
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