o2 / exhaust question

[GT400]

First off i have searched, but apparently not for the right thing...

I am in the process of fitting a 1uzfe into a mk3 supra, and and curious how people deal with aftermarket exhausts deal with the whole 4 o2 sensor thing. surely there are people running around with out cats... how does the car handle this, or is there some modification for this? any help would be great, as i dont want to get done with the swap and find out im out of luck. Thanks in Advance!

D.

 

[JBrady]

The is one before cat and one after cat per bank. The before cat O2's are fine without cats. It is the second set that will misread. You can purchase O2 simulators that send the "clean" signal back to the ECU or you can run cats. Do a search on www.corvetteforum.com under O2 sims.

 

[GT400]

The is one before cat and one after cat per bank. The before cat O2's are fine without cats. It is the second set that will misread. You can purchase O2 simulators that send the "clean" signal back to the ECU or you can run cats. Do a search on www.corvetteforum.com under O2 sims.

awesome, thanks.

 

[xirforever]

Im running test pipes right now and it doesnt throw up any error codes and normally that ecu will throw up a code for anything that it doesnt like. I figure if it doesnt throw up any codes then all is well... or am i wrong?

 

[DonyLingus]

you can also make your own o2 sensor simulator by wiring in a 1K Ohm resistor in place of the oxygen sensor. that costs about 2 to 3 USD and they don't even have to be anywhere near the exhaust system.

 

[Tacoma_Kyle]

Thanks for mentioning that, I was curious if you could do that.

 

[cjsupra90]

you can also make your own o2 sensor simulator by wiring in a 1K Ohm resistor in place of the oxygen sensor. that costs about 2 to 3 USD and they don't even have to be anywhere near the exhaust system.

I am not saying that you are wrong, but that does not make any sence cause the O2 generates its own voltage based on oxygen content in the exhaust unless the car is equiped with a wideband O2 system then the computer sends a voltage and receives an adjusted voltage back based on oxygen content, but I have not heard that any of the toy/lex v8's having wideband systems form the factory. Now yes you might need a resistor for the heater circuit to not show a citcuit open or shorted fault, but other then that there is no way to wire in a resistor to create a sensor simulator.

The simulators that you can buy take a voltage tap from the heater circuit and regulate it down to a known good voltage (IIRC .2 to .3 volts) and send it to the ECU. Computer is basically looking for a differance between the per cat unit and the post cat unit to ensure that the cat is working. With that said, you would think that leaving unhooked would be just fine as then there is no voltage which is then going to deffinitly be less then the pre cat unit(s), but most cars, this wont work as the computer is programed to know that there should be some voltage other wise there is a problem. Not all vehicles have this monitoring system and some can just be unhooked and work fine, but most will need a simulator of sort

 

[Celsiorous]

Hi, im running no cats and have not modified the after cat o2 sensors in my 90 Celsior. What would the affects of this be? Sorry i guess this is a noob question. In the next few weeks I will be removing the stock exhaust and going full after market. Just wondering whether I should do something about those o2 sensors while im there.
Cheers

 

[cjsupra90]

Hi, im running no cats and have not modified the after cat o2 sensors in my 90 Celsior. What would the affects of this be? Sorry i guess this is a noob question. In the next few weeks I will be removing the stock exhaust and going full after market. Just wondering whether I should do something about those o2 sensors while im there.
Cheers

Being a 90 and therefor an OBD1 diagnostics system, you shouldn't have any problems. Is the MIL (malfunction indicator lamp) on and has the car changed the way that it is running? If the light is not on and the car is running fine then I wouldn't worry about it. If the light is on then find out why and make sure that it does not have to do with the rear O2 sensors. If it is then you will need some form of simulator for them.

 

[Celsiorous]

Being a 90 and therefor an OBD1 diagnostics system, you shouldn't have any problems. Is the MIL (malfunction indicator lamp) on and has the car changed the way that it is running? If the light is not on and the car is running fine then I wouldn't worry about it. If the light is on then find out why and make sure that it does not have to do with the rear O2 sensors. If it is then you will need some form of simulator for them.

Thanks, I dont have an error light so I guess its OK. The cats were removed before I bought the car so im not sure if it affected the way it runs, there are no miss's or anything abnormal so im thinking its OK.
Thanks for clearing that up for me.

 

[GSMnow]

I have the complete 93 LS400 service manuals, and the only error code listed for the sub O2 sensors is if they don't go to a rich reading after several seconds of > 70% throttle driving. This would be an open loop condition which should be richer than 14.7. The cats will absorb oxygen when running lean and release it when running rich so the transition from rich to lean will be much slower after the cats, but the mixture will still change. So, even after the cats, the mixture will go rich after a period of time. If the ECU does not see this rich condition it reports a failed sub O2 sensor. Most of the O2 simulators I have seen just oscillate at a couple hertz between .2 and .8 volts so the ECU sees both a rich and lean reading so it must be working. OBD II is a bit trickier as they try to see the delay from the pre cat O2 to the post cat O2 to calculate how well the cat is working.

Gary M.