Johnny G Pipe

I have just disconnected mine to try to diagnose idle hunt (see separate thread). The car is perfectly happy without it. I guess it optimises mixture, as wikipedia says:

Automotive oxygen sensors, colloquially known as O2 sensors or lambda sensors, make modern electronic fuel injection and emission control possible. They determine if the air fuel ratio exiting a gas-combustion engine is rich (with unburnt fuel vapor) or lean (with excess oxygen). Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to improving overall engine operation, they reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of excess air in the fuel mixture and cause smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 70s, along with the 3-way catalyst.

..but I thought I'd read somewhere of folks not using one. Maybe track cars when consumption and emissions are less important, and WOT is the order of the day?

And hey, I know what closed and open loop means now!

springer3

In the US it is illegal to tamper with emmissions controls. In Georgia, they verify the cat and O2 sensor during mandated annual inspections.

Johnny G Pipe

In the UK emissions are part of the mandatory annual inspection, but pre 91 or 92 cars (I think) have less strict constraints - pretty sure the cat bypass guys with 93 MY cars have to reinstall their cats once a year..

Superunknown

I dont have an o2 sensor and it runs fine. WHat i dont know is if anything was changed/adjusted after the cable was cut. I read somewhere that you have to jumper something in the ecu?

Johnny G Pipe

Ahaa..do you have a cat? Do you have MOT emissions issues?

You can jumper the ECU seemingly quite easily to run in sensorless mode. I found it on a search but cant find it again..can anyone give me an idots guide?

911addict

In the uk they check the emission gases, its not important per se whether there is a cat on or not. This is regadless of model year although pre 93 are less stringent figures.
There are also different types of cat bypasses, some of which look just like cats but are empty, so a garage wouldn't know any different.

Greg_L

I've run without one for some time, but am in the process of reinstalling one, as its a bit fuel smelly.

To jumper, Porsche make a little white plastic connector plug that connects to a 2 pin (i think) wire than comes out of the ecu.

I have a bypass that has a hole for a new one, so i bought a bosche one and reinstalled it, removed the jumper, but then it ran like crap, really rough. So i put the jumper back on and its fine again. Now i heard that you have to wind in the adjuster on the back of the airflow meter when you put an o2 sensor back in the loop. Is this the right thing to do?

Red rooster

Johnny ,

On the DME loom a bit back from the DME connector is a three pin white socket . Plug a 928.607.422.00 Variant plug in and the DME is not looking for an O2 sensor any more !
This was a Rest of the World set up for countries that only had lead fuel. The fuel /timing maps are unique for this configuration . It will need the idle mixture to be played with , maybe on a regular basis . Access to the adjuster on the AFM is tricky .

Unless I was faced with a desperate situation ,this is not a set up I would want to use .Up to you !!

Geoff
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KS400200,the oldest 964 on Rennlist,unless you know differently !

Superunknown

I have a cat bypass. MOTs can be tricky as the car runs mighty close to the emissions limit. I think it something like 3.5% and my car failed first time. After a long blast it showed 3.2% or something. I was thinking of re-fitting the o2 sensor but then the hastle of working out the jumper and adjusting the afm thingy has made me put the thought on the back-burner.

Superunknown

Has anyone got a picture of the jumper in place?

Greg_L

Geoff, am i right in thinking i can wind the AFM adjuster right in to get the closed loop setup going properly? Or will it take more careful setup with an exhaust probe?

964rh

Mine runs with a cat bypass and a jumper'd ecu.
I think the jumper is a 928 part no. - try 928 607 422 00. Pet lists as a coding plug on the dme page.

pat056

I've got a 1993 RSA race car that apparently is running too lean. If I disconnect the 02 sensor and have stock electronics, what will it do to the AF misture? If you say it's "smelly", that that mean it make the mixture's more rich? Emmisions aren't an issue. I do want to run unleaded fuel.

Greg_L

yep.

Red rooster

Gregg,

The O2 sensor is , by a very small fuel amount , taking the idle/low part load
fuelling up and down , around the desired level .
The best move is to adjust the idle tail pipe mixture to around 1.0% CO using the AFM adjuster . This is with the O2 sensor disconnected and no Cat involved . Then connect the O2 sensor and watch the tail pipe mixture . With no Cat you should see somewhere between 0.5% and 1.0% , gently going up and down .
The Cat is there to remove the 0.5 to 1.0 % CO if emission laws demand that .

Years ago Porsche UK used to supply a Non Cat coding plug and a Cat bypass with no provision for an O2 sensor . It brought me a fair amount of " fix it " business !! This DME set up was incorporated by Porsche design to allow the 964 to be sold in countries with no unleaded fuel .
People thought they would get more power but did not realise what the No-Cat
DME calibration was !!!

Geoff
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KS400200,the oldest 964 on Rennlist,unless you know differently !

Hope that helps .