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cis problem
I had a similar problem with my 1982 SC a few months back where it would intermittently go full rich to around 10.0 AFR. After doing some testing it turned out to be a problem with the WUR allowing the warm control pressure to drop drastically resulting in such a rich mixture that the O2 sensor system could not compensate.
I had the WUR rebuilt and the problem was solved.
I will also mention that at one point I had a problem where I was not seeing any enrichment on my AEM air fuel ratio gauge when the throttle went past the 1/3 enrichment switch which directs the system to go to "open loop", I have the mixture set so it achieves 12.7 -13.1 at full throttle depending upon ambient air temperature. It was somewhat difficult to determine the cause due to the fact that the 1/3 switch checked out OK etc. It turned out that the WUR "push valve" return line in the fuel distributor was clogged causing the control pressure to be so high that the system was unable to achieve the mixture enrichment as it should when in "open loop" past 1/3 throttle. I forced some air through the WUR return line to the Fuel distributor which cleared the blockage.
Just as info, I have an addition bung installed in my cat bypass for the for the AEM wide band O2 sensor. I have found that being able to monitor the air fuel ratio has been invaluable in seeing and solving any cis issues.
Dave
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