AFR 20+ Until Warmup MAF connected or disconnected

[mediumrareintexas]

???

This situation is really strange to me. I'm sure that someone out there has the answer. Why would the AFR be so high when cold? Seems like the computer is taking control after warmup. Then the AFR drops to 12 or so. It does the same whether the MAF is connected or disconnected.

[pknowles]

Air injection to light off the cats at start-up. Mine goes to around 19-20 as well for about a minute. The time is dependant on the ECT.

[mediumrareintexas]

Thanks for the response. So what you are saying is that this is a normal condition. Any comment on the MAF connected or disconnected? It seems like it goes into closed loop whether the MAF is connected or not. But maybe I am not interpreting the results correctly.

[pknowles]

Yes it's normal. The operation of the Air pump has nothing to do with the MAF, so you can do what ever you like to the MAF and the Air Pump will still come on at start-up. The Air Pump turns off at some ECT, but I don't remember it off the top of my head. Understand that the AFR of 19~20 that you are seeing is not the AFR coming out the the combustion chamber. The extra air added into the exhaust to light off the cats is done right at the exhaust manifolds so the gases flowing over the sensors (downstream of the air injection) will show lean because there is a lot of extra air in the exhaust.

Closed loop is disabled at some ECT as long as the O2's are hooked up and maybe a few other things (I'm not 100% sure as to everything that is required). I know the MAF is not required for open loop operation as the PCM uses a Speed Density calculation to calculate the air flow and corrects the trims based on the O2 readings.