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Old 01-24-2002, 04:28 PM   #1
daytontp
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2005 Honda S2000
New Formula Red

Default A/F Ratio Change Relocation Question???

I am planning to buy a 2 1/16" AutoMeter A/F Ratio gauge, specifically the Carbon faced UltraLight model. I understand that the 2002 WRX has a wide band (0-5 volt) O2 sensor in the front and a short band (0-1 volt) O2 sensor in the rear. I also understand the AutoMeter gauge only works with a short band O2 sensor. I also understand that with a stock exhaust the reading would be more accurate before the front cat than after the rear cat. I am also planning to put a turbo back exhaust and uppipe in the car, from M2 Performance. As well as M2's TMIC. And, I understand the CELs issues with this exhaust mod. I am not planning on buying an EGT gauge. I have several questions, which if you read all of them you may understand where I am going with them.

1. What is the thread size of the EGT bung on most aftermarket uppipes? I am assuming 1/8" NPT or 1/8" BSPT.
2. What is the thread size of the WRX's rear O2 sensor threads? And, will it fit into the bung in most aftermarker uppipes?
3. If I put the uppipe and turbo back exhaust on my car, would the reading at the rear O2 sensor be more accurate than with the stock exhaust? I am guessing yes.
4. Now, lets say I have the uppipe, a turbo back exhaust and a MIL Eliminator capacitor installed on the rear O2 sensor (to stop the CELs). If the A/F gauge is hooked up to the rear O2 sensor, will it effect the A/F Gauge readings? I am guessing NO if the gauge is connected to the wire inbetween the O2 sensor and the capacitors. And, YES if the gauge was connected to the wire inbetween the ECU and the capacitors.

Any suggestions will be welcomed!!!
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Old 01-24-2002, 04:44 PM   #2
daytontp
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Default

I forgot to mention something.

I am not planning on moving the rear O2 sensor to a location before the turbo. I would buy another rear O2 sensor and put it in the uppipe, or near there. Both of the stock O2 sensors would stay in their correct locations. Which brings up the question as how to wire the new one up. How would voltage wires be setup so the sensor would work? Because if you were to wire the sensor into the location the rear O2 sensor is wired, it would trip CELs. At least I guess it would.

Any suggestions!!!
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Old 01-24-2002, 04:53 PM   #3
Jon [in CT]
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1) The stock EGT sensor's threading may be M8 x 1.0, but I don't really know. I doubt it's 1/8" npt.
2) The O2 sensor's threading is M18 x 1.5 and definitely won't fit into the EGT bung. You could have the EGT bung removed and an O2 bung welded on in its place.
3) I agree that the rear 02 sensor would be more accurate with only one cat ahead of it instead of 3.
4) I believe that if you connect your gauge somewhere between the sensor and the MIL Eliminator resistor, it will not be affected by the MIL Eliminator.
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Old 01-24-2002, 09:46 PM   #4
bobgrice
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Default

To clarify, the EGT sensor threads are definitely not 1/8" NPT. They are M12 x 1.25.

I just had to make some custom parts for my up-pipe, so I purchased a high speed tap and die in this size.

If anyone would like to buy or borrow the tap & die, just PM me and let me know.
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Old 01-24-2002, 10:12 PM   #5
daytontp
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Thanks for the info!!!!

1. Does anyone know how to wire the O2 sensor, if I was going to add a 3rd one on the uppipe?
2. Does anyone have an idea what the rear O2 sensor would cost me at the dealer?

I am probably just going to put it on the rear O2 sensor and then just deal with it not being as accurate until I get my turbo back exhaust.
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Old 01-24-2002, 11:06 PM   #6
Jon [in CT]
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An unheated O2 sensor (one wire) can be purchased for about $30 at your local auto parts store. If it's mounted in the uppipe, it won't need a heater and having only one wire should make wiring it to your gauge simpler.
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Old 01-25-2002, 07:05 AM   #7
bobgrice
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Use caution when mounting an O2 in your up-pipe. I understand (not from experience, though), that it is NOT a good idea to put it here, I imagine due to higher temperatures in the long run.

As I mentioned, mine is mounted 4" after the turbo on my downpipe, which from what I understand is the prime placement. My BPM downpipe had a bung, so it made it too easy.

I totally agree with Jon to purchase the CHEAPEST single wire O2 sensor you can find and wire it up. The one I purchased was heated and I should have just saved the money and gotten a cheaper one. The heater is to get a better reading more quickly, but, if you're taking care of your car and letting the oil temp get to operating conditions before jumping on your engine (several minutes), your O2 sensor will be plenty hot to give you good readings. The only advantage of the heated O2 is that I have good readings within 20 seconds of turning the key (engine running or not).

Just my $.02 (perhaps $.03).
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Old 01-26-2002, 03:17 AM   #8
wrx_in_efx
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I just hooked up a halmeter A/F guage and I spliced in to the Rear o2 sensor signal wire. It takes a minute or so for it to heat up but It is accurate. Check out Rifts hm page, he shows you exactly how to do it. www.projectwrx.com
LAter.

Cory
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