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Thread: 2005 STS4 O2 sensor replacement and misfire. HELP PLEASE!

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    mkosharkii's Avatar
    mkosharkii is offline Cadillac Owners Fanatic
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    Angry 2005 STS4 O2 sensor replacement and misfire. HELP PLEASE!

    Hey guys,

    I have an ongoing problem here that's driving me out of my mind. I'll start from the beginning.

    I've had a sporadic P0420 since I bought the car a few months ago. Other than having to try and get it to the dealer when the code was present, the cat's failure has been transparent.
    I put about 1400 miles on the car last week when I drove from Norfolk, VA to Groton, CT and back. Besides the 0420 code coming up and clearing on it's own once during my time up there, no problems. AWESOME car to drive long distance in, second only to my Vettes I had in my young single life
    Anyway, I returned here to Norfolk on Sunday night. On Monday morning, when I started the car, I immediately had a definitive misfire. Quick examination revealed that 9/10 intake manifold bolts were loose, one was totally backed out, and another about a quarter inch out, the rest not even hand tight. Some stumbling was present on acceleration during lower RPMs. It didn't throw a code until later that day. Scan revealed P0300 (random misfire) and the elusive P0420. I drove DIRECTLY from AutoZone to my dealer in order to take advantage of the 0420. Come Wednesday, the car is done with two new catalytic converters. Still missing and minor stumbling at low speed.
    That afternoon / evening I began to eradicate every potential source of a vacuum leak I could find. I have replaced:
    -Intake manifold gaskets (torqued manifold to 89 in/lbs in proper order)
    -Both crankcase vent tubes
    -Throttle body gasket
    And I ruled out the brake booster hose by removing it and blocking the connection on the manifold temporarily, although it does need a new hose.
    I also carefully inspected the plenum ducting for proper seal. Looks good.
    Yesterday, I went back to AutoZone to see if any new codes had populated. Lo and behold, P0300 had been vanquished and replaced by the more pointed P0306 (cylinder #6 misfire). It is accompanied by it's pal, P0050 (Bank 2 Sensor 1 O2 sensor heater circuit).
    I have verified the O2 sensor (or wiring) is bad, as the heater circuit has an open. I worry the dealer may have damaged the wiring on the sensor. Otherwise, thats pretty ironic timing. I also pulled the plugs from cylinder 4 and 6, they look the same (good). I also swapped coils from 4 and 6. While I was in there, I reseated the injector plug for #6. Once that was all done, I started the car. NO MISS!
    For the rest of the day yesterday in various driving conditions, the miss was gone. I went to AutoZone and cleared the codes. Naturally, the P0050 returned almost immediately.

    This morning, the miss was back the moment I started the car.
    I haven't scanned codes yet to see if it followed the coil to cylinder 4.

    End results:
    -Who knows how to replace the driver's side pre-cat O2 sensor? I can barely see the thing from underneath or on top. Have any of you done this on a Northstar STS or SRX?
    -Any ideas on the miss? I'll update in a few hours on what cylinder is missing now, provided a code has been generated.

    Thanks in advance!

    Last edited by mkosharkii; 11-01-13 at 12:14 PM. Reason: sp

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  3. #2
    mkosharkii's Avatar
    mkosharkii is offline Cadillac Owners Fanatic
    Automobile(s): 2007 SRX4 N* MRC, 2014 Corvette Z51 3LT, 1979 KZ1000 LTD
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    Just to update, no misfire code has reappeared yet. The misfire does seem to die off once the engine is fully warmed up. I have tried to find data on how to troubleshoot these coils with a multimeter, but no dice. Anyone out there?!

  4. #3
    mkosharkii's Avatar
    mkosharkii is offline Cadillac Owners Fanatic
    Automobile(s): 2007 SRX4 N* MRC, 2014 Corvette Z51 3LT, 1979 KZ1000 LTD
    Join Date
    Sep 2011
    Location
    Norfolk, VA
    Age
    32
    Posts
    230

    Re: 2005 STS4 O2 sensor replacement and misfire. HELP PLEASE!

    I bought a set of coils off Amazon. My intent was to use the one I needed and sell the rest, but the individual plugs for the coils are a new style. The entire pack must be switched out in order to use the new harness. My problem with misfires is resolved, but I still have a bad O2 sensor. Is there really NOBODY who has changed Bank 2 Sensor 1 on a V8 STS or SRX?


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