O2 Sensors not needed?

[speedracer07]

I recently dropped a 3.6L in my 86, the work was done at a shop in northern NV, just realized that the O2 sensors wore not hooked up, to their credit I supplied all the parts including the racing exhaust, no heat, the car is hard to start in specially when warm.
Question can this engine run w/o the O2 sensors?
Also used LWFW and racing clutch from Patrick Motor Sports, the obvious issue with engine dropping the RPMs so quickly the, the engine stalls (Lighter rotating mass)! I bought an used DME with performance Chip and Air Intake, looking for a solution where I can keep my LWFW
Thanks for any input!

[Steam Driver]

I personally think you need the O2 sensors if you’re running any sort of EFI. Without them I would expect a serious drop in power and driveability. Not sure about the hot start issue relative to the O2 sensors, but maybe there are some other sensors (engine temperature, intake air temperature) not hooked up as well? Those would definitely affect hot start.

[proporsche]

the day i got my 911 back in 1996 i disconnect the O2 sensor...think about it..most of the 911 Carreras in the World do not use oxy sensor at all...
Ivan

[jerrykrug]

I am in Reno, and was just curious what shop in Northern NV did the work, sorry cant help with the o2 question.

Thanks Jerry

[rattlsnak]

Originally Posted by proporsche

the day i got my 911 back in 1996 i disconnect the O2 sensor...think about it..most of the 911 Carreras in the World do not use oxy sensor at all...
Ivan

Yes, back then in certain countries and they have different control units.. all modern USA EFI cars ( 1996 and up.. the start of OBDII) use an O2 sensor. Without it, the car will be default to a pre- programmed limp mode. That being said, he didn’t say what year 3.6 he has. A 964 3.6 is very different then a 993 3.6.

[proporsche]

Originally Posted by rattlsnak

Yes, back then in certain countries and they have different control units.. all modern USA EFI cars ( 1996 and up.. the start of OBDII) use an O2 sensor. Without it, the car will be default to a pre- programmed limp mode. That being said, he didn’t say what year 3.6 he has. A 964 3.6 is very different then a 993 3.6.

yes true, i was mainly thinking of prior 964 and on models
Ivan

[70SWT]

Originally Posted by Steam Driver

I personally think you need the O2 sensors if you’re running any sort of EFI. Without them I would expect a serious drop in power and driveability. Not sure about the hot start issue relative to the O2 sensors, but maybe there are some other sensors (engine temperature, intake air temperature) not hooked up as well? Those would definitely affect hot start.

As an anecdotal data point, I can confirm I have seen odd running issues on two 3.2L cars when the O2 sensor was unplugged.

[AlKidd]

You can program EFI to run without it but you end up with the equivalent of a carburetor if you do. Its perfect the day you do it. If temp/humidity/altitude changes its no longer set correctly.

[David Inc.]

This has me thinking. Backdating to the early headers O2 cars only get one sensor in the 1-3 bank. How do the ECUs account for control while only looking at half of the system?

[76FJ55]

Originally Posted by David Inc.

This has me thinking. Backdating to the early headers O2 cars only get one sensor in the 1-3 bank. How do the ECUs account for control while only looking at half of the system?

the older cars are all batch fire systems and can't control individual banks. Having 2 separate O2 sensors would supply the computer with 2 different values which the computer could only control to 1 of. the deviation between the readings would cause conflict in the trim as the computer could only attempt to make one of them correct. On the 3.2 the O2 sensor is mounted on the left side of the car, but actually after the merge collector for the left and right bank just before the catalytic. with aftermarket headers you may find a system that has O2 bungs in a single bank, in which case, the assumption is that both banks are running the same if you are truly only monitoring one bank, and the computer trims the system to correct the AFR on that bank.

[David Inc.]

Thanks. I guess the issue would become an injector on the unmonitored bank going way rich or lean causing misfire that the ECU wouldn't see at all. That's where the nut behind the wheel would need to be listening for indications like that and checking flow.

[speedracer07]

My apologies, the 3.6 came out of 1990 964 car, I did own a 993 C4S and it had 4 O2 sensors, not that familiar with 964 motor.
The engine runs fine besides the staling at low RMPs, given the LWFW and racing clutch ,the revs are amazing.
I talked to Steve Wong regarding the staling issue, he suggested I need a custom chip for the setup I have now, he thinks that modifying the idle speed will take care of the problem of staling.
That will be my next step.

Thanks for your input!

[GH85Carrera]

O2 sensors are not expensive, and they only weigh a few ounces. At best they improve the performance and fuel mileage of the engine. Most people prefer that.

I can't think of any reason NOT to use in on a 3.2 or later engine unless you have converted to carbs. No super rich running or too lean with the sensor hooked up.

What am I missing that would make anyone not use one? Now the air pump from the SC, or thermal reactors is a very different thing.