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Old 10-13-2003, 09:47 PM
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Gilly Gilly is offline
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
Glad you got it running better. Let me explain just a few things though:
You stated the car was in "closed loop". This is incorrect. If anything you should consider it open loop. When it is "open loop" it means the car hasn't warmed up enough for the O2 sensor to properly work, and the engine is operating with the mixture set almost exclusively by the engine coolant temp sensor. Once the engine warms up sufficiently, the mixture is being set by the O2 sensor, this is known as "Lambda". What that means is that when the O2 sensor senses "rich mixture", the control module drives the mixture to the lean side. When the O2 sensor then senses "lean mixture", the control unit then enriches the mixture. This is Lambda, once the engine warms up the mixture is set using this Lambda procedure, contantly switching between rich and lean. Being in Lambda operation is also called "closed loop", the relationship between the O2 sensor and control unit is "closed". If the control unit isn't operating in Lambda, because the engine temp isn't warm enough, it is "open" loop, no relation yet between the O2 sensor and control unit.

However what was going on with your car was different. The control unit was essentially "dead" because of the blown fuse in the OVP, so the system has sort of an emergency running mode, which is called "fixed operating mode", or FOM for short. This is different than being in open loop. It's not even taking the engine coolant temp into account, the mixture is a constant, which is why it would start OK warm, but not very well cold, the mixture is set to run best at normal operating temp, that's how it's set up to run in FOM, at normal operating temp, no variation.

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