993inNC

Steve Wiener. I believe you'll find he supports the theory, and would suggest the same. Let me know if you find otherwise

clib

I am not sure where you ended wtih this. It sounds like they are in the catbypass but unplugged? is that correct. Without being heated in the exhaust stream i believe they will get dirty quickly and aren't able to be cleaned later so they will not be any good down the road. Not a big deal most likely but just know you'd probably have to replace if you wanted to go back to using them.

Joe@Fabspeed

HI All

This is Joe at Fabspeed Motorsport USA.

Porsche 993 1996 to 1998 were the 1st geneation OBD 2 cars. These cars and all late model Porsche cars have 4 wire Oxygen sensors. The extra wires are HEATED oxygen sensors and that is why they are hot when you zip tied or safety wired them under the car.

These 1st generation OBD2 cars will operate 100% fine with the 2ndary O2 sensors either installed with an O2 simulator or safety wired/attched under the car breathing ambient air or perhaps unplug them.

When I made 993 catbypass pipes back in summer of 995 for 1996 Porsche 993 cars..........I advised DE drivers and PCA POC Club Racers to just safety wired the 2nd o2 sensors and everyone was fine 15 years ago.

When I made catbypass pipes for my 993 and Rafael Llopiz for a PCA POCONO IMSA Long Course club race as exhaust was "FREE" ............rafael and I had the only Porsche 993s that walked away from the 3 other stock 993s ............litterally 5 to 6 cars length on each straight...........

Joe Fabiani
Fabspeed Motorsport USA
fabspeed.com

shadow993

Thank you. Right now they aren't in and it doesn't appear they need to be for the car to run correctly.

If I get a cel or a fault code before my 9/11 inspection, I will hard wire and plug them back in.

CorrdoBrit

I'll be surprised if you pass inspection without the cats. Won't your emissions exceed permissible limits?

shadow993

They don't hook anything to the exhaust. They just hook up a computer via obdii port and look for codes.

sjagernauth

I have a '95 and installing cat bypass shortly. What's the wisdom on the O2 sensor for an OBD1 993?
There is an O2 sensor port in the cat bypass. What are the consequences of plugging in vs tie-wrapping out of the way? Will the car run lean or rich? I'd prefer rich obviously.

Bill Verburg

the US '96 up cars are OBD2 and have pr-cat and post-cat O sensors, your '95 is OBD1 and only has 1 pre-cat O sensor. Install it in which ever bank of the cat by-pass you choose and it will work just the same as before, ie no issues

geolab

If an oxygen sensor pre or post cat is in open air, voltage will read 0.1v.
0.1v reading or unplugged o2 sensor , a 993 DME switches to open loop or operation without oxygen sensor. Fault code 24
the post cat O2 sensors are for catalytic function control? not only
The DME heats the sensors and monitors them through their gamma voltage oscillation (difference). Under heavy load and/or high engine speed, the DME shuts down sensor heating.
If post cat sensors in open air, DME heating of pre-cat sensors is not stopped, which normally kills the sensors and often small pieces of it land on the catalyst cartridge and destroys it.

geolab

O2 sensor pre-cat as in my car, regulates air intake and fuel intake.
If you un-plug it and tie it somewhere? your car will run normal because as said above, the voltage of the sensor will be 0.1v and the DME will switch to no sensor program.
One O2 sensor , since it monitors both banks, is heated by the DME for 180 seconds only, and heating is shut off after
By normal I mean it is a pre-programmed cartography that the DME follows. Thus air density, altitude and all the factors are not taken into considerations. You might think its normal, but it is not optimum.
.............and some think they are going faster.

Quadcammer

ok now hold on. The pre-cat 02 sensor obviously needs to stay in place.

Whats to say the post-cat needs to be in place. From my understanding, the computer reads how much voltage is required to keep the sensor at a certain temperature...the temp drop caused in part by the flowing 02 in the exhaust. If you open air it, the air flowing around the car would cause that sensor temp to fall.

geolab

I think I understand your question, if it is why the post cat needs to be hooked.?
the DME measures exactly what you said , the difference of voltages of the pre-COMPARED to the post.
at normal idle, our pre- 993 sensors read 0.45 volts and the post read 0.57 volts where the TIME factor of 800 millisecond is taken into consideration for heating the pre-sensors.
In high idle and under heavy load, the voltages of the pre and post-sensors approach to very close together, with roughly 100 litres of gas flow per second at full rpm, the voltages are near equal. the heating of the pre-sensors is shut off.
if the post sensor is in open air, the voltages will never come close, and heating is maintained.

Quadcammer

ok, but what measurable effect does that have on the the running of the car.

Even if heating is maintained, adding or pulling fuel is an awfully lousy way to make the cat more efficient.

I don't like the open air idea either, but I don't think its gonna cause much if any difference in the fuel trims.

Bill Verburg

Goelab, Isn't your car an OBD1 RoW? if so it has only the 1 pre-cat O sensor and it works like the US '95s

geolab

I agree, but it won't change fuel trims when you will need them neither.
with change in air temperature/density, mixture is maintained as is....
if you change altitude going uphill, you will run very rich, etc...
regards