No closed loop operation

[RexHarris]

I am working on a 2000 Corvette with a tune and long tube street headers that was all done around 3 years ago by someone else. The car came in with 2 DTC's (P0134 &P0154) for insuficient switching on both front O2 sensors that set a check engine light. The car had what appeared to be Bosch rear sensors installed in front and no rear sensors installed. After talking to the header manufacturer and doing the wiring harness checks I installed 2 new AC Delco rear sensors in front bungs per the manufactures recommendation. Upon start up the front O2 sensors are still reading between 450-475mV and the car will not go into closed loop operation and stays open loop while monitoring with a Tech 2. During a test drive the O2 readings went to around 800mV with an occasional switch to 300mV and stayed operating open loop. The MAF, IAT, MAP, and ECT readings are all correct for the operating conditions. I read the tune with HP Tuners and all of the table values appear to be correct and the car should be going into closed loop operation. My next step is going to be trying a Bosch sensor to see if I can get the car to go into closed loop and the 2 DTC's to stay cleared. Has anyone ran into a problem similar to this. Thanks Rex

[Google]

post your tune and a log

[Montecarlodrag]

You have a wiring problem or bad/incorrect sensors. Even with the worst headers the O2 should switch. Constant reading about 457 mV means no electrical connection from the sensor to the PCM.

Unplug O2 sensors from bungs and turn igintion key on (don't start engine). Touch the tip of sensors to see if the are hot. If they aren't you have a problem with the heater circuit or sensors are bad.
A cold sensor will never switch.There is nothing you can change in the tune if you have a bad wiring/sensor.
Even if you set the tune to be always in Open Loop, you can see the O2 sensors switching.

[5.7ute]

Even if you set the tune to be always in Open Loop, you can see the O2 sensors switching.

Huh. An o2 sensor is a reactionary device. It will only show switching voltage if the pcm is varying fuel delivery.
OP were the 800mv & 300mv areas corresponding with accelleration (800mv) & decelleration (300mv)?
It does sound like a heater or tune related issue though.

[Montecarlodrag]

Huh. An o2 sensor is a reactionary device. It will only show switching voltage if the pcm is varying fuel delivery.
OP were the 800mv & 300mv areas corresponding with accelleration (800mv) & decelleration (300mv)?
It does sound like a heater or tune related issue though.

I have seen it. In open loop the AFR changes even at idle or cruising. It's the same with a wideband, you never get a flat line

[Google]

post your tune and a log

[5.7ute]

I have seen it. In open loop the AFR changes even at idle or cruising. It's the same with a wideband, you never get a flat line

Watch the pulsewidth.

[Throttle]

post tune

[mowton]

Has the car been tuned before? Is it perfromance setup or stock?

Some "reputable" tuners will actually cut the O2 wires to make sure the car stays out of closed loop operation.....

As stated several times above, post your tune and a scan (include the .cfg file as well) so we can check it out.

Ed M