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Thread: Oxygen sensor location

  1. #1
    Senior Member Joel Hauser's Avatar
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    Oxygen sensor location

    I have a question about Oxygen Sensor location. I built a roadster using a 1996 mustang GT 4.6 L motor with SOHC n.p.i. heads. It is pretty much a stock engine, although I rebuilt it after having the cylinders bored. I have not installed cats, EGR or charcoal canister. I've installed a new fuel pump, filter, injectors, fuel pressure regulator, coils, plugs, wires, and sensors all around. I purchased the Factory Five custom headers. I did not use J pipes. Neither the headers nor the side pipes come with bungs for O2 sensors. Like many other builders, I drilled holes into the side pipe collectors and welded bungs to the collectors, and have installed the sensors at this location.
    Most of the time the car runs extremely rich, smells terrible at idle, stalls at idle and deceleration, and misfires and hesitates on acceleration. At higher RPMs, like over 3000, everything seems to smooth out.
    Thinking the car needs a tune, I purchased a tuner from BAMA/SCT. After I sent them a recent data log, they wrote back that the signal from the sensors is fluctuating all over the place, writing "From the data logs that you sent in the Fuel Trims are all over the place and showing a MAX lean condition at times and a MAX rich condition at other times. The O2 sensor voltage readings are also flat lining in the log. This could be part of the issue. Depending on what sensors are being used here they may not be functioning properly. I always recommend Ford Motorcraft for these sensors as they tend to work the best followed by NTK sensors. The other thing that could be occurring here is if you are using any wiring harness extensions with the Mustang. We see these fail or come faulty and it will prevent the sensors from operating properly."
    I have ordered new ford sensors, like BAMA has recommended.
    I've noticed that there has been some discussion and controversy on the forum about placement of the sensors. Most builders say putting them in the side pipe collector is the best place to put them. Others say to put them in the header pipes for number 4 and 8 cylinders, because it will be closer to the exhaust port and therefore hotter.
    I'm considering buying a set of Dorman stock cast iron exhaust manifolds and using the J Pipes, but would prefer not to; the custom FF/hooker headers were very expensive, and should work better than the stock manifold.... Shouldn't they?
    Do you have an opinion regarding O2 sensor location. is the collector location too far from the heads; could puddle water be splashing up and causing it to give inaccurate readings. Do you get accurate readings if you install the sensors in only the 4 and 8 exhaust header pipe?
    I've got to get this fixed; the car is not driveable because of the stalling, hesitation, and smell.
    Thanks for your input.
    Joel
    Last edited by Joel Hauser; 03-06-2019 at 08:34 AM.

  2. #2
    Senior Member Joel Hauser's Avatar
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    Although no one replied to my post, I thought I'd update the status.
    The engine is is fixed, and running great. It turns out it was the ecu. Having replaced all the sensors with no improvement, the only thing left was the ecu. I purchased a new rebuilt from Flagship one. BAMA wrote a new tune which included disabling the PATS, and took into consideration the few mods I made, and success!! No misfiring, and no rich smell. The car has really great power. Such a relief, and just in time for spring.

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