I have a manual fan switch and a 180 degree thermostat. I turn the switch on when car gets hot(half mark on the temp gauge).

When the car warmed up, I was monotoring the rich/lean condition via the SES LIGHT on the dash and when I turn the fan on manually the car went into the open loop.(light flashing very fast)

Probably because the coolant was cooling down and having an effect on the CTS and ECM.

1. What is better for performance open or closed loop?
2. Should I worry about car staying in open loop most of the time or not?

Thanks.

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89Iroc, 305 TPI, WC T5, 3.08 Posi, Headers, Hooker Y-Pipe, 3 inch over the axle, Flowmaster 80, No Cat, Aluminium Driveshaft, Ported Plenum, Air Foil, K&N, All free mods,

 

At Wide Open Throttle (WOT) the ECM goes into open loop mode. During open loop, the ECM ignores the O2 sensor output and reads preprogramed info for fuel and air.

Because the oxygen sensor does not perform properly at low temperatures, two modes of operation are employed. The modes are referred to as "closed-loop" and "open-loop." Open-loop mode is utilized during engine warm-up. During open-loop the fuel delivery system does not recognize or use the information from the oxygen sensor until a temperature of approximately 600 deg. F is obtained. Once the operating temperature is achieved, the system enters closed-loop mode were the oxygen sensor information is routed to the ECM to control the fuel and air delivery.
Open vs. Closed loop does not effect power as much as it will effect your gas mileage. Your O2 sensor maintains a 14.7 to 1 air fuel mixture for gas mileage and emittions.
I recommend getting a fan switch that automatically turns your fan on/off for you at the right temp.

 

Constant open loop will be horrible for your gas mileage. You will be in a constant state of fuel enrichment and your TCC will not lock up sending your fuel economy to zilch.

 

I don't think you'll get cool enough to go into open loop with a 180 stat, even with the fans on all the time...as long as the stat is working properly.

And just for clarification, WOT isn't "open loop", but is called "power enrichment" or similar, as is a little different than open loop.

 

I don't think you were seeing an "open loop" condition either. Closed loop usually occurs around 140* coolant temp. At least with my car, anyway. Not sure what you were seeing, though.

Ken

 

There of course is a third option you might be seeing. The "limp home mode". An emergency mode when your car sees trouble codes....