6G Celicas Forums

Hello all,

After lots of mods and tuning on my 7A, ive decided to completely get rid of both my 02 sensors, I have an S-AFCII on there for tuning purposes.

I was wondering if anyone has ever put in a resistor in the O2 sensor plug in order to "simulate" a proper O2 sensor function.

If not, does anyone know the correct resistance needed for both the O2s to read proper A/F ratio?

PS. its for a 94 7AFE

This post has been edited by 94celicadude: Mar 10, 2010 - 4:09 PM

...safc is not a standalone, it just modifies signals going to the computer to alter the computers output to add more fuel or reduce fuel. you need O2 sensor feedback and a computer to run the safc2/safc. sounds like what you're desiring is a standalone, but unless you're pushing a full engine build with crazy cams or a hybrid 7age or forced induction then a standalone is overkill. try a more advanced piggyback like an e-manage since you'll be able to control timing as well as fuel and fuel control will be much better.

I am aware of what the SAFC2 does, but i am not looking for an explanation for that, I am asking if anyone knows what the ECM is looking for resistance wise in order to be a correct A/F ratio.


Not trying to be rude, just trying to find out some info.

its not looking for resistance, but you know all that already right?

This post has been edited by Bitter: Mar 11, 2010 - 7:42 PM

you need the o2 sensors, even if you trick the car into thinking they are there its a bad idea. The resistance in the o2 sensors changes all the time and must communicate with the map sensor for proper AF ratios, even with safcii.

quite on the contrary, it actually is looking for a given resistance.

And yes cheesy I understand that the resistance is constantly changing, i was just curious if anyone knew of the correct resistance when the A/F is near optimum stoichiometric efficiency.

I appreciate the help and the info so far.

Has anybody ever found any proper way that to eliminate 02 sensors on OBDI cars?

orly? care to back up your statement that a stock zirconia narrowband sensor creates resistance in reference to rich/lean conditions? go on, please do. please tell me how that works.

You can buy emulators on ebay. You need to create a square wave, a resistor is not going to do that, you need to build a 555 timer or other square wave oscillator circuit. Cutting both sensors out of the system seems like it's going to get you a blown motor unless you also have EGT with that setup? Relying on maps leaves you no way to account for changes. Honestly I don't know how your car would even run in anything but the conditions you tuned it for.

You may have read somewhere that you can fool the ECU with a resistor. Well you can but that is only for the heater circuit, the other two of a 4 wire O2 sensor. It stops it throwing a CEL code if the O2 sensor pre-heater is missing/faulty. It has nothing to do with the air/fuel mixture.

This post has been edited by tankd0g: Mar 14, 2010 - 7:49 PM

Guys, when using a meter, how do I check bank 1 and 2 (o2 sensors) and their volts? What should they correctly read?

Use the stickies on the top of this engine section. There's a link to a full CEL code and how to diagnose.

Ok, thanks!

my car being a 94 has OBDI still and the O2 sensors are only single wire sensors.

Basically what i would do if i got rid of O2 sensors would be running what is commonly known as a speed density tune, where the engine performs most efficiently at the temperatures it was tuned at.

Toyota was smart enough to program a "Safety" mode into their ecu in order to be able to run the car still even if both O2 sensors went out, now while this mode is just an extremely conservative mode, it adds fuel to ensure an over rich mixture and disables advanced timing to ensure that no detonation occurs.

I was hoping somebody may have found a way to bypass the factory O2 sensors on an OBDI car without having to go full stand alone ecu.

Thanks for the input to all.

Btw did some research and found this... i was on the wrong path, but this may only apply to OBDII O2 sensors... but i am sure that OBDI O2 sensors are not far off from this method of functioning.

An Oxygen sensor is a chemical generator. It is constantly making
a comparison between the Oxygen inside the exhaust manifold and air
outside the engine. If this comparison shows little or no
Oxygen in the exhaust manifold, a voltage is generated. The
output of the sensor is usually between 0 and 1.1 volts. All
spark combustion engines need the proper air fuel ratio to
operate correctly. For gasoline this is 14.7 parts of air to one
part of fuel. When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.

The sensor does not begin to generate it's full output until it
reaches about 600 degrees F. Prior to this time the sensor is
not conductive. It is as if the circuit between the sensor and
computer is not complete. The mid point is about 0.45 volts.
This is neither rich nor lean. A fully warm O2 sensor *will not
spend any time at 0.45 volts*. In many cars, the computer sends
out a bias voltage of 0.45 through the O2 sensor wire. If the
sensor is not warm, or if the circuit is not complete, the computer
picks up a steady 0.45 volts. Since the computer knows this is
an "illegal" value, it judges the sensor to not be ready. It
remains in open loop operation, and uses all sensors except the
O2 to determine fuel delivery. Any time an engine is operated
in open loop, it runs somewhat rich and makes more exhaust
emissions. This translates into lost power, poor fuel economy
and air pollution.

The O2 sensor is constantly in a state of transition between high
and low voltage. Manfucturers call this crossing of the 0.45
volt mark O2 cross counts. The higher the number of O2 cross
counts, the better the sensor and other parts of the computer
control system are working. It is important to remember that the
O2 sensor is comparing the amount of Oxygen inside and outside
the engine. If the outside of the sensor should become blocked,
or coated with oil, sound insulation, undercoating or antifreeze,
(among other things), this comparison is not possible.

This post has been edited by 94celicadude: Mar 24, 2010 - 10:30 PM

a standalone still uses O2 sensor feedback for closed loop dude, it just lets you tell it what you want it to do.