no o2 sensors?

blue87lx · Nov 28, 2005

a buddy of mine runs his car without o2 sensors and it seems to run good. he runs consistant 11.7-11.8's. i asked him about it and he told me the shop that he has his work done at told him that it wouldnt decrease performance. i thopught it would decrease performance because wont the computer go into limp mode?

HISSIN50 · Nov 28, 2005

The puter would just default to running rich. For a track only car, perhaps this works. Otherwise, since O2 input is ignored at WOT, I would run with O2's.

vristang · Nov 28, 2005

Wow!

Personally I would be looking for a new mechanic if I heard something like that. Maybe it does work great on a track car.

I would think that power would be better if you let the computer know exactly what was going on, instead of trying to trick it into doing what you want.

I would suspect a power loss if running too rich. Maybe he isn't running that rich?

I would like to see a dyno sheet without the O2s, and then a run with O2s. That would be interesting.

jason

blue87lx · Nov 28, 2005

what would happen if you were running o2 with no cats/longtubes?

Blk91stang · Nov 28, 2005

two of my friends are running WITHOUT o2 sensors and their cars run perfect on the street and on the track. I also wonder what this affects..

vristang · Nov 28, 2005

Can you guys post some of the mods these guys are running while not using the O2s?

This is pretty interesting.

Michael Yount · Nov 28, 2005

Guys - when you go wide open throttle - the car goes into open loop and IGNORES the O2 sensors. ALL OF OUR CARS run without O2's at wide open throttle.

With no O2's the car doesn't go into some planned 'rich' mode -- it just won't go into closed loop. Everytime you start your car cold - it runs in open loop until the O2's get warm enough to generate reliable signals for the ecu to react to.

My car spent it's first 6 years/25K miles with the O2 sensors not hooked up. I never knew anything was wrong (no drivability or fuel mileage 'clues') until I pulled the motor to do H/C/I -- that's when I discovered the guy that did the conversion didn't plug the O2 sensor part of the harness into the main harness.

The only difference I noticed was going from 22-23 mpg on the highway stock with no O2's to 25-26 mpg on the highway with mild H/C/I and O2's hooked up.

vristang · Nov 28, 2005

Michael Yount said:
Guys - when you go wide open throttle - the car goes into open loop and IGNORES the O2 sensors. ALL OF OUR CARS run without O2's at wide open throttle.

With no O2's the car doesn't go into some planned 'rich' mode -- it just won't go into closed loop. Everytime you start your car cold - it runs in open loop until the O2's get warm enough to generate reliable signals for the ecu to react to.

My car spent it's first 6 years/25K miles with the O2 sensors not hooked up. I never knew anything was wrong (no drivability or fuel mileage 'clues') until I pulled the motor to do H/C/I -- that's when I discovered the guy that did the conversion didn't plug the O2 sensor part of the harness into the main harness.

The only difference I noticed was going from 22-23 mpg on the highway stock with no O2's to 25-26 mpg on the highway with mild H/C/I and O2's hooked up.

I have no doubt that it would still run without the O2s. My thoughts are that if the motor is heavily modified, it could run very poorly when compared to a stock motor w/o O2s. Things like larger injectors and larger TB / MAFs, will all have an impact on the performance.

In my mind I am seeing the ability to run without O2s as being possible (without major consequences) in mildly modified stangs, and much more difficult as the motor approaches either supercharges or Nitro.

Not trying to offend. I just want to understand these situations better.
Thanks all.
jason

Michael Yount · Nov 29, 2005

The ecu has what are called 'adaptive strategies' that allow it to alter how it thinks. Over time it will make adjustments for things -- like sensors that aren't as effective as they used to be, and even driving style. There is a limit to how far it can alter things as it 'learns' about changes that are occurring. So it has some ability to adjust even with the O2 sensors gone.

No doubt -- the further you change things beyond what the design engineers of the ecu had in mind for it's operational parameters, the more likely you're gonna need to alter the ecu (chip, pms, tweecer, etc.) - with or without O2 sensors.

There are a number of tuners out there who prefer to do their heavy-mod tuning (lots of boost for example) with no O2 sensors so the computer stays in open loop.

88GT17MA · Nov 29, 2005

Kinda off topic.....I got a set of 4 wire 02 sensors. I still have the 02 harness but there are only 3 wires that go to each 02 sensor. I need to wire the 02 sensors into the harness but I dont know which wires to use. Can anyone shine some light on this? my 02 sensors still have connectors on them, but I was planning on cutting them off to hardwire them into the harness.

Michael Yount · Nov 29, 2005

I guess I'd try and obtain the appropriate 3-wire sensor for the car....even if you're able to wire them up, how do you know they're gonna generate the right signal for the ecu if they're not the right sensors for this application? Maybe I can learn a little something here....

jrichker · Nov 29, 2005

88GT17MA said:
Kinda off topic.....I got a set of 4 wire 02 sensors. I still have the 02 harness but there are only 3 wires that go to each 02 sensor. I need to wire the 02 sensors into the harness but I dont know which wires to use. Can anyone shine some light on this? my 02 sensors still have connectors on them, but I was planning on cutting them off to hardwire them into the harness.

The 4 wire sensors have a separate ground for the heater. If you can successfully identify the heater ground you can do one of two things:

1.) Wire it to the signal ground.This is not recommended since the heater current can overload the wiring, or voltage drops in the wiring can offset the O2 sensor output signal.

2.) Wire it to a separate body ground. This requires a little extra wire and some effort to find a place to scrape some paint off to make a good ground. This is the best approach if you join the ground wires together and ground them to the engine block.

blue87lx · Nov 29, 2005

the guy that i know has a 347 stroker edelbrock heads and intake custom cam 24lb injectors and upgraded mass air throttle body not sure of the sizes for that and a complete fuel system off the top of my head.

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