O2 sensor without cat

[FJ80HI]

My cats are removed yet the two o2 sensors are still in the exhaust pipe. I have driven this way for 70000 miles and never had a check engine light. The rig has always run great and never an engine problem. I get 12 mpg no matter how fast I drive or if I run ac. Always have heavy carbon deposit on inside tail pipe but engine burns no oil. Always thought it ran rich. Thinking seeing o2 sensors are original on this 1991 with 190k miles. Should I change the o2 and do I need both and if the o2 were bad would I have a check engine light. Is the mpg low or typical or could it be bad o2 input to computer

 

[petegangies]

My cats are removed yet the two o2 sensors are still in the exhaust pipe. I have driven this way for 70000 miles and never had a check engine light. The rig has always run great and never an engine problem. I get 12 mpg no matter how fast I drive or if I run ac. Always have heavy carbon deposit on inside tail pipe but engine burns no oil. Always thought it ran rich. Thinking seeing o2 sensors are original on this 1991 with 190k miles. Should I change the o2 and do I need both and if the o2 were bad would I have a check engine light. Is the mpg low or typical or could it be bad o2 input to computer

You may not always get a check engine light. If it were me, id be replacing both with OEM Genuine new ones. Ecu uses them for fuel trims in closed loop operation.

 

[FJ80HI]

You may not always get a check engine light. If it were me, id be replacing both with OEM Genuine new ones. Ecu uses them for fuel trims in closed loop operation.

Am I ok without the cats? O2 sensors will still work?

 

[petegangies]

Am I ok without the cats? O2 sensors will still work?

Yes. My aus delivered 94 has no cat and runs a single o2 sensor.

 

[TX80CC]

I am running no cats or 02s, the CEL is not on but I did the paper clip Obd1 trick and it had a code for both 02 sensors. I also get 12mpgs. Trucks run good otherwise.

 

[FJ80HI]

I am running no cats or 02s, the CEL is not on but I did the paper clip Obd1 trick and it had a code for both 02 sensors. I also get 12mpgs. Trucks run good otherwise.

Thanks. I did an internet search and AI came back with reply that the o2 sensor upstream of cat is used by computer to control engine air fuel and the one downstream of cat is used to control emissions. I deleted the egr. If this is true I could connect the downstream o2 ( by electrical wiring and not move sensor) and see what happens as far as engine performance. And if true only need one 02. Or as you did none. My exhaust is original and 190k miles and by the looks of the o2 fitting I do not want to mess with it. I think I will wait until I need new exhaust to mess with it seeing the engine runs well and the mpg seems to be about normal

 

[TX80CC]

Thanks. I did an internet search and AI came back with reply that the o2 sensor upstream of cat is used by computer to control engine air fuel and the one downstream of cat is used to control emissions. I deleted the egr. If this is true I could connect the downstream o2 ( by electrical wiring and not move sensor) and see what happens as far as engine performance. And if true only need one 02. Or as you did none. My exhaust is original and 190k miles and by the looks of the o2 fitting I do not want to mess with it. I think I will wait until I need new exhaust to mess with it seeing the engine runs well and the mpg seems to be about normal

I do have headers back exhaust and it sounds like it still runs the same as yours. I’m with you just run it as is until you need new exhaust.

 

[TX80CC]

Yes. My aus delivered 94 has no cat and runs a single o2 sensor.

Where is your 02 located at? Thinking about intalling on my manta exhaust.

 

[petegangies]

Where is your 02 located at? Thinking about intalling on my manta exhaust.

almost directly underneath the drivers seat (RHD). We dont have a cat converter, just a small muffler. Below you'll see the twin downpipes that join to the exhaust manifold and then run down the firewall and under the chassis. After the o2 is the muffler, then it joins to the mid-pipe which has another large round muffler, then one final join near the rear diff for the rear muffler out the tailpipe.

 

[TX80CC]

almost directly underneath the drivers seat (RHD). We dont have a cat converter, just a small muffler. Below you'll see the twin downpipes that join to the exhaust manifold and then run down the firewall and under the chassis. After the o2 is the muffler, then it joins to the mid-pipe which has another large round muffler, then one final join near the rear diff for the rear muffler out the tailpipe.


View attachment 4081307

Thanks, I think I can just weld the bung in a similar location. My concern is it even going to make a difference in how rich the truck runs since it used to have cats. It’s a jdm import. Truck doesn’t run bad at all just rich and s*** mpgs.

 

[Rifleman]

I did a test by installing some test tubes in place of my 2 cats on my 94 Land Cruiser. My 94 uses wide band O2 sensors before the inlet on the cats, with a closed loop voltage of 2.5 to 3 volts before i removed the cats.

I can say that the reduction in the back pressure had an effect. First my gas mileage went up from 9 miles a gallon, to 13 to 14 miles per gallon. Then it dropped down to between 11 to 12 miles per gallon.

When the mileage dropped in hooked up my Snap On MT2500 code scanner (this scanner shows live data as the engine is running) to again check what the the O2 sensors voltage was reading. Both sensors were reading 5 volts which is rich, i think this was due to the lack of back pressure making the engine think it was running lean. This condition in my test did NOT trigger any trouble codes, so no check engine light on the dash.

 

[Lead Head]

Thanks, I think I can just weld the bung in a similar location. My concern is it even going to make a difference in how rich the truck runs since it used to have cats. It’s a jdm import. Truck doesn’t run bad at all just rich and s*** mpgs.

The front O2 sensors have nothing to do about the cats - they're responsible for controlling the engine fueling.

 

[landtank]

You want to make sure the sensor are wired correctly. If they are crossed the readings will max out. This is because any adjustment to one cat is actually influencing the other cat.

 

[FJ80HI]

Op here. Pic of my setup. Cats out pipes in. Thought one o2 before cat and one after. I was wrong. Both before cat. I leave as is for now as runs ok

 

[landtank]

Both O2 sensors are pre cat however the front manifold should be connected to the O2 harness the that runs down the front firewall and the O2 harness that connects to the pipe from the rear manifold should be coming from over the transmission bell housing

 

[FJ80HI]

I did a test by installing some test tubes in place of my 2 cats on my 94 Land Cruiser. My 94 uses wide band O2 sensors before the inlet on the cats, with a closed loop voltage of 2.5 to 3 volts before i removed the cats.

I can say that the reduction in the back pressure had an effect. First my gas mileage went up from 9 miles a gallon, to 13 to 14 miles per gallon. Then it dropped down to between 11 to 12 miles per gallon.

When the mileage dropped in hooked up my Snap On MT2500 code scanner (this scanner shows live data as the engine is running) to again check what the the O2 sensors voltage was reading. Both sensors were reading 5 volts which is rich, i think this was due to the lack of back pressure making the engine think it was running lean. This condition in my test did NOT trigger any trouble codes, so no check engine light on the dash.

Both O2 sensors are pre cat however the front manifold should be connected to the O2 harness the that runs down the front firewall and the O2 harness that connects to the pipe from the rear manifold should be coming from over the transmission bell housing

I will verify. Thanks.