2nd gen O2 sensor question

[ITSRotary]

Just installed roadrace header and it has no provision for the O2 sensor. What now? I'm running stock motor, FI, etc and was under the impression I had to run with the sensor. Any help very much appreciated.

Steve

[AS-RACER]

We had a friend cut a hole and weld in a threaded bung in the exhaust pipe just past the header.

[Silkworm]

Mine came with the bung already installed, most race muffler shops should be able to do this for you, but the average midas probably won't.

PaulC
88 PS1/ITS RX-7

[mlytle]

any muffler shop should be able to do this. all it is is a weld. i just drilled the hole myself, carried it down to the local midas, and they did it in 5 minutes.

marshall

[ITSRotary]

Thanks guys. That was my thoughts. Just trying to break the habit of doing it right the third time. Appreciate the help.

Steve

[C. Ludwig]

You don't need the O2 sesnor. Running without it is one way to force the FI into open loop. It's only used for idle and part throttle anyway. When you're WOT you're running in open loop. Without it connected you'll force the car into constant open loop and will be able to control the mixture with fuel pressure.

Chris

[GEO46]

That's fine and dandy, but doesn't it kinda go against the GCR and ITCS where to paraphrase it says, if it doesnt say you can do it, you cant?

[Silkworm]

Could easily argue, IMHO, that it's a smog device.

PaulC

[TURN9]

...still waiting for my ITCS and GCR. If the Cat's aren't being used, then the O2 sensor isn't going to work anyway. It isn't going to register to the fuel injection system without the burn-off heat from the cat/s. It isn't working anyway. It falls into that "...it has to be there but does it really have to work?" areas.

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Corey L. Clough
Ex-1st Gen, Pre-2nd Gen
[email protected]

[EV]

I thought an o2 sensor, to work correctly needed to be upstream of the cat?

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[Silkworm]

I can't confirm or deny Corey's statement, but the O2 sensor is definitely before the cats. Stock, the O2 sensor is in the exhaust manifold, just ahead of the cat.

Note, newer cars (OBD II) may have a 2nd O2 sensor after the cat, to ensure that the cat is working correctly.

PaulC

[Chris Wire]

And since exhaust if unrestricted, use of the O2 sensor is not necessarily required, IMO.


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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35

[C. Ludwig]

OK. We can tune the FI by altering the readings of sensors with resistors or the like. And exhaust is open. So we can unplug the O2 sensor and not put a bung in the new exhaust. Toss the sensor in the glovebox or tape it to the bottom of the floor pan if ya wanna keep the weight low.

Chris

[TURN9]

Is the exhaust open from the stock exhaust manifold back, or cat on back?

Without the 02 sensor, the FI System will constantly run in the "warming up" mode. It will still get readings off the coolant temp, throttle sensor, air sensor... but what happens when it doesn't recieve a "ready" signal from the cat? If you remove the 02 Sensor, there is no return signal, and if you leave it in, it won't work. "Houston, we have a problem!"

Better yet, remove the 02 sensor and plug it with an EGT Gauge. Get a good digital one from Aircraft Spruce. It will be your best tuning device. Case closed.



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Corey L. Clough
Ex-1st Gen, Pre-2nd Gen
[email protected]

[wlfpkrcn]

For a street vehicle to go into closed loop it must have the O2 sensor installed. On a race car you don't need to worry about it because the ECM does it's own thing at WOT. The ECM never knows the cat is working on an OBD1 car because there is no O2 sensor downstream of the cat to check its efficiency. The O2 sensor creates its own voltage by lack of oxygen, and is most effective once it reaches 600F. The voltage that the sensor produces is then interpretted by the ECM, which then will change injector pulse width to keep the car running at a air to fuel ratio of approx 14.7-1. So the way I see it the O2 sensor is an emmisions device only and can be removed.

Eric