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Thread: +50% STFT bank 1 during idle only??

  1. #1
    Lifetime Member samh_08's Avatar
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    Oct 2008

    Default +50% STFT bank 1 during idle only??

    As the title says. What would cause such a thing? Poor performing o2 heater on that bank is the only thing I can think of.

    All bank 1 injectors are firing as well as spark to all of them.

  2. #2
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    Jul 2008


    Other than a massive exhaust leak.

    Is it only at Idle?
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..

  3. #3
    Lifetime Member samh_08's Avatar
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    Oct 2008


    Yes, it is only at idle. Once I get on the gas both of the banks are the same as each other.

  4. #4
    Joe (Moderator) joecar's Avatar
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    Apr 2003


    Like Shawn said check for air leaks.

    Then, swap O2 sensors across banks.

    Then, swap injectors across banks.

  5. #5
    Lifetime Member samh_08's Avatar
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    Oct 2008


    Sounds good Joe. Is there a way to test the o2 sensor heaters? I really feel like this is the issue..

  6. #6
    Lifetime Member ChipsByAl's Avatar
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    Feb 2006


    Turn the key on engine off, both front O2's should swing from bias voltage to a lean value in about the same time. If the heater is working then the O2 sensor voltage should change.
    "Trash that carb and get Injected!"

  7. #7
    Lifetime Member swingtan's Avatar
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    Jul 2007


    Here's an example of what happens when O2's play up. In this example I was doing some WOT tuning so was not really concerned with O2's and trimming. I used a std. PID selection that just happened to include the STFT's but had no intention of using them. the car did not have a dedicated WB O2 port in the exhaust, I just removed a NB and tied it up out of the way. As the tune would check the O2's for operation, this would force the tune into OL mode, as the O2 would always be reading fresh air.

    The tuning went well, but every so often when coming to a stop, the WB showed that idle mixtures were progressively getting richer, but not all the time. I enabled the display of the STFT's to see that they were adding fuel. Here's a pic of the log file...

    What I believe is occurring, is that the O2's were being enabled, but only when idling and not all the time. Because one O2 was reading freash air, the PCM was adding fuel to try and richen things up. The NB O2 never indicated that the additional fuel was being effective, so the PCM kept adding fuel. This is seen in the WB O2 data. In this log, trim s got to about 15% before the PCM realised the O2 for bank 1 was "faulty" then it dropped to OL mode. The funny thing was that it would switch back to CL at times.

    There was nothing really wrong with the tune or the O2's in this case, as one was not in the exhaust stream. Once it was returned to its normal position, All was good again.


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