New Headers and Exhaust In - Oxygen sensor delete (1 Viewer)

[Formulaonehd]

Ok mudderz

The next exhaust and headers are finally in, my god what a pain the headers were to get in and the old manifolds out. Im happy to do a write up if anyone wants? although there are a few write ups already, plus a couple of videos on youtube.

Now, lets start with how much better it sounds and flows with the new system, First drive concluded the headers upgrade is a must for anyone who cares about letting these engines breathe better.

My issue is with the 02 sensors, or lack there of. The P/O must have done the 02 delete as my two upstream sensors were plugged up and i cant seem to find a trace of the plug harness although im sure its hiding somewhere. I only have 2 as its a 2000 model so no post cat sensors have ever been on it.

Now, the fuel smells pretty rich like it always has although the car still runs perfectly well, i had assumed the richer smell was like this because of bad 02 sensors but of course learnt there were none when we pulled the old manifolds out. Hmmm no sensors how does the ECU know what AFR to run??

Without them do you need to run premium or anything? and also without them and a bigger exhaust flow would the ECU require remapping or piggy back? Its running well but i do wonder if the aftermarket sticker on the fuel cap that says "premium only" was put there as a result of the 02 delete or just a paranoid dude who doesnt like regular. Bit stumped here guys hoping some gurus here can shed some light on 02 sensors and the need and effect of not having.

Cheers

 

[gatormark91]

Ok mudderz

The next exhaust and headers are finally in, my god what a pain the headers were to get in and the old manifolds out. Im happy to do a write up if anyone wants? although there are a few write ups already, plus a couple of videos on youtube.

Now, lets start with how much better it sounds and flows with the new system, First drive concluded the headers upgrade is a must for anyone who cares about letting these engines breathe better.

My issue is with the 02 sensors, or lack there of. The P/O must have done the 02 delete as my two upstream sensors were plugged up and i cant seem to find a trace of the plug harness although im sure its hiding somewhere. I only have 2 as its a 2000 model so no post cat sensors have ever been on it.

Now, the fuel smells pretty rich like it always has although the car still runs perfectly well, i had assumed the richer smell was like this because of bad 02 sensors but of course learnt there were none when we pulled the old manifolds out. Hmmm no sensors how does the ECU know what AFR to run??

Without them do you need to run premium or anything? and also without them and a bigger exhaust flow would the ECU require remapping or piggy back? Its running well but i do wonder if the aftermarket sticker on the fuel cap that says "premium only" was put there as a result of the 02 delete or just a paranoid dude who doesnt like regular. Bit stumped here guys hoping some gurus here can shed some light on 02 sensors and the need and effect of not having.

Cheers

You aren't getting a CEL from the O2 sensors not being hooked up?

 

[Formulaonehd]

nope, even more odd. Could the P/O have just reset the code or would they just come back again?

 

[white_lx]

In a typical situation the air/fuel mixture is set by the oxygen sensor information. The ECM will continuously adjust between slightly rich and slightly lean so on average you have a balanced, stoichiometric, mixture. Other sensor data is used to verify oxygen sensor operation, such as the MAF.

If the oxygen sensors are missing, the ECM has no clue about the actual mixture leaving the exhaust (lean or rich). So it will use MAF data to measure air mass flow and use known injector and fuel properties to determine the matching amount of fuel for that amount of air.

Since there is no feedback from oxygen sensors in that case, it is very easy to be off. E.g. a dirty MAF, unmetered air from a small vacuum leak, a problem with fuel pressure regulation or a dirty fuel injector. Also the fuel composition will affect the the mixture ratio as e.g. fuel containing ethanol using less air to burn per volume of fuel. Since the feedback loop from the oxygen sensors is missing the control will become open loop. You would need to be very lucky and have perfect MAF data and no vacuum leaks and lab fuel to have the perfect mix ratio.

Now how the PO could circumvent the oxygen sensors is a mystery to me. Is there an aftermarket ECM? Or maybe this is possible with the Australian spec models?

 

[Formulaonehd]

In a typical situation the air/fuel mixture is set by the oxygen sensor information. The ECM will continuously adjust between slightly rich and slightly lean so on average you have a balanced, stoichiometric, mixture. Other sensor data is used to verify oxygen sensor operation, such as the MAF.

If the oxygen sensors are missing, the ECM has no clue about the actual mixture leaving the exhaust (lean or rich). So it will use MAF data to measure air mass flow and use known injector and fuel properties to determine the matching amount of fuel for that amount of air.

Since there is no feedback from oxygen sensors in that case, it is very easy to be off. E.g. a dirty MAF, unmetered air from a small vacuum leak, a problem with fuel pressure regulation or a dirty fuel injector. Also the fuel composition will affect the the mixture ratio as e.g. fuel containing ethanol using less air to burn per volume of fuel. Since the feedback loop from the oxygen sensors is missing the control will become open loop. You would need to be very lucky and have perfect MAF data and no vacuum leaks and lab fuel to have the perfect mix ratio.

Now how the PO could circumvent the oxygen sensors is a mystery to me. Is there an aftermarket ECM? Or maybe this is possible with the Australian spec models?

Thanks for the info mate. Well i can tell you that the economy of the vehicle and how it runs is probably on par with other UZ100 cars here but everyone that i know of has 02 sensors. I'll have to have a look but I have no idea if it does have an A/M ECM. Where would this be located? in the same location as the stock ECM?

My thoughts were this too, how could you bypass the 02 sensors without an A/M ECM?

 

[AllLC]

The CEL would come back on after a reset if there was no O2 sensors. Also, Toyota USA recommends premium fuel only for my 99.

 

[neoworm]

Maybe this would help? Says rear but all it does is output a voltage to simulate what the sensor outputs and it is adjustable. Don't see why it wouldn't work for eliminating the front sensors as well.

urd-rear-sensor-simulator-universal

 

[white_lx]

Thanks for the info mate. Well i can tell you that the economy of the vehicle and how it runs is probably on par with other UZ100 cars here but everyone that i know of has 02 sensors. I'll have to have a look but I have no idea if it does have an A/M ECM. Where would this be located? in the same location as the stock ECM? My thoughts were this too, how could you bypass the 02 sensors without an A/M ECM?

Optimal fuel economy does not necessarily coincide with optimal emissions (stoichiometry 14.7:1) and or optimum power. See the example below. Optimal fuel economy in that particular example is 15.4:1


By Clamothe - Own work, CC BY-SA 3.0, File:Ideal-stoichiometry.jpg - Wikimedia Commons

Are you able to spot any modifications to the wiring harness? Strange that the plugs disappeared. Probably very unlikely that someone changed the ECM to A/M just to save some oxygen sensors. But this could be a spec option for non NA vehicles maybe?

Maybe this would help? Says rear but all it does is output a voltage to simulate what the sensor outputs and it is adjustable. Don't see why it wouldn't work for eliminating the front sensors as well.
[\quote]

As far as I know the rear sensor simulators typically produce a slow varying voltage (or constant). Nothing like the repsonse of the primary sensors. But maybe primary simulators exist as well.