71GSSDemon said

This was the statement I remembered and needed reconfirmation of. I am hoping for dyno data to prove the case. It would maybe take an O2 in a header head pipe for a cylinder and force the cylinder to run very fat and see. Like increase the duty cycle of just 1 injector. Read how that cylinder reacts and total exhaust also. Or a cylinder drop test to turn Ignition off on a single cylinder. I wonder of I could get this data at work....

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Johnny Mac said

I use an AEM on my 408. If the O2 fails, it seems to default to stoich and freeze there. As others have pointed out, it reads unburnt O2, so any misfire, or a fouled plug, can cause false lean readings. This is why the bolt on TBI systems get a false "Bad" diagnosis. They run in a default open loop when cold (rich) and if you start it and move it 10 times, and shut it off cold (think of moving it around a garage in the winter) it soots the plugs, runs worst, soots the plugs more, and when it finally kicks to close loop when warm, it reads the unburnt fuel from the fouled plugs, and pours even more coal to it.

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