i have been dealing with some problems. i have a otc scanner that a browered from a shop, and with it i found that my car runs in closed loop all the time. I put a 160 stat in and had madz28.com tunning done, it runs about 178 on the gauge and on the scanner it jumps around from about 170-179 never getting out of closed loop. The only time i can get it to come out of close loop is shutting the car off for a few minutes and the starting it back up , it will stay out of closed loop then after a minute it chages back to closed loop. also the car idles alittle rough, and runs alittle rich(being rich is because its in closed loop right?).
I have not check the ECT sensor with a meter or cheked the voltage of the harness yet. If you have any ideas tell me because im stummed!. thanxs for the replys!

 

Sounds like its completely normal. When you start the car, its in open loop. After 1) O2 sensors heat up and start to work, 2) coolant reaches 120-140degF, and 3) timer times out (2-3 minutes), it goes into closed loop. At that point, the PCM is looking at the O2 sensors and adjusting the fuel to keep it running close to 14.7:1 A/F ratio. It doesn't "run rich because its in closed loop" unless there is something giving faulty O2 readings, like exhaust leaks, misfires or faulty sensors/wiring.

When you go WOT, the scanner will still indicate "closed loop". All that means is that the PCM has set the flag for "close loop enabled" = all of the three conditions I listed above have been met. It doesn't mean its using the O2 sensors for feedback to control the A/F ratio at WOT.... just means that the PCM has found all 3 conditions to be met.

 

so its normal to have it run in closed loop know matter what? becuase thats what its doing. Its in open loop starting cooled then when it reaches 150 it goes to closed and stay there, no matter what. i would think that something is wrong, im i right or wrong?

 

Without causing a DTC, the only thing you can do to put it in OL is go WOT. The new GM vehicles are now CL even at WOT. It takes the new wide band O2's to accomplish this and they are somewhere between $300 and $600.