Did I say closed loop? Of course, I meant open loop. And yes, I do understand the FOM mode, but thought that the 02 sensor still would be sending a signal to the ECU. I guess that without the fuse, the control unit is as you stated, "dead" and no sensor information is being used to determine the air/fuel mixtures. But while in the FOM mode would making mixture adjustments then have any effect on the running of the car? The adjustments that I made were mostly mechanical, not electrical from what I can tell, as it looks like it just mechanically adjusts the air sensor plate height to determine the air/fuel mixture. So I am thinking that it should still effect the running of the engine to some degree even while in FOM.