o2 sensor necessary?

some have suggested that disconnecting the o2 sensor can contribute to a better running engine. is this true?

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Adam Nitti
www.adamnitti.com
'85 Carrera
'74 3.0 CS

Considering what the 02 sensor does, I doubt it. I understand an O2 sensor can tell the computer how rich or lean the engine is running. Then the computer makes adjustements based on the O2 sensor, throttle position, air-flow, air temp, engine temp. etc.

I have heard of others say it makes the engine run better.

Of course it would really depend on how the computer was programmed.
US (Chevy, Ford etc) when they lose the O2 sensor they go into a "Limp-Mode". This is where the computer goes to a pre-programmed settings for the engine and turns on the "Check-engine light".

So I presume the same for Porsche. The computer then may run a little more rich. There-by improving power.
It may also run TOO rich, giving you bad power and bad gas mileage.

Either way I think you will get worse gas-mileage.
Will it improve the performance? Perhaps.
Will it clog the Catalytic converter? I suspect over time.

I prefer the reliability /power and gas mileage.

You may want to try a new O2. As a "lazy" O2 can cause the engine to think it is running rich when in fact it is running lean. Or even the other way around.

Try it and let me know :-)

Nick
'85 911

i'd be willing to try a new sensor if they weren't so darn expensive. i think they're over $200 for our cars. my car isn't running badly right now, but i think my low end performance suffered a little bit when i had the car adjusted to pass emmissions...

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Adam Nitti
www.adamnitti.com
'85 Carrera
'74 3.0 CS

Adam,

Avoid the P-tax!!!!!!!!!!!
Have seen them in Excellence (this month, pg 177) for $30-70, depending on whether you have a 1 wire, or 3 wire. Pelican may also have them.

A friend of mine bought his from (OHMIGOD) JC Whitney... even had Bosch on the box when it arrived.

I beleive most 02 sensors are universal fit. Let the idiot's that pronounce it POORSH pay dealer prices. (maybe they'll even have to sell a few gold chains and nugget rings tp do it!)

Good luck

The 02 sensor is a VERY important part of ANY electronic fuel injection system-the computer will regard data from the 02 sensor as more important that any other sensor it is sampling on any given engine. Removing it from the system will force the computer to substitute a fixed value (or values) for the data it should be seeing from the 02 sensor, and it will enter the "limp home" mode-which is exactly that-it'll get you home, but that's about it. If you suspect the 02 sensor may be bad, it's easy to test-with the engine at operating temperature, the 02 sensor will output a very small DC voltage averaging around .5 volt (half a Volt DC)-if you use a digital mulitimeter, you can see the voltage rapidly changing above and below this value, but averaged, it will be .5 volt or so. If you've ever run leaded fuel, gas additives with lead in them, or used RTV silicone anywhere around the engine, most likely the 02 sensor has been ruined , and needs to be replaced. Remember, any fuel injection system is just that-a SYSTEM, and you can't just change or remove part of it without affecting the rest of the system (usually in a negative way).

With it disconnected the computer assumes a voltage of 4.5 v from the sensor, i.e. stochiometric. The computer detects the presence of the 02 sensor by sampling the input for dithering voltage of a certain characteristic. In this way, when you start you motor and the 02 is cold, the computer operates in open loop ('limp?? home') with 4.5v on the 02 input wire. When the 02 sensor gets hot enough to start producing a dithering voltage the computer goes into closed loop and adjusts mixture according to the voltage is sees at the 02. This closed loop mode can cause a slight hunting at idle as the mixture sweeps from lean to rich and back. This voltage goes from about 0.1 to 0.9 with .45 representing about 14.7:1 air/fuel. If it runs better disconnected at part throttle it may be compenstating for other problems (fuel pressure reg, injectors etc). I have had my last 2 Porsches running with the 02 disconnected. I did not bother about ruining the cat as I had taken them off anyway. My current 88 Carrera has a MAF conversion with an air/fuel indicator and fuel computer. I use the 02 sensor only to supply a reading to the air/fuel indicator and use the fuel computer to make the car run slighly rich under all load conditions and rich (about 11 or 12:1) under WOT. If the 02 was active it would constantly try to correct my slightly rich condition at part throttle and make a rough ride. I think the original system holds the air/fuel within a tight range (lean most of the time) for fuel economy and cat life. At WOT the 02 is bypassed, but it's at part throttle that it can cause an uneven ride. The slightly rich set up I have also makes the car run a little cooler and gives my peace of mind when driving hard. Drivability is much improved and it's nice to 'see' whats going on with the air/fuel ratio and be able to control it interactively.

can someone help me to confirm the location of this sensor? it's on the drivers side, with 3 wires sticking out connected to 2 individual components on the side of the compartment, correct?

(the p-tax, eh?... :-) you guys are gonna have to fill me in on all your secret parts connections....)

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Adam Nitti
www.adamnitti.com
'85 Carrera
'74 3.0 CS

Thats the one. The complete assembly from a dealer would come with the gromet for the plate around the engine and the proper plug. The generic 3 wire sensors are considerably cheaper as pointed out, but you need to solder them into the old wires after cutting the old sensor off. Well worth the $100+ saving.

I bought a Bosch sensor for a Buick and cut the plug off. Match the black to the black and the white to the white wires and you are in business...$39.95 at Pep Boys. Go Manny, Moe and Jack!

In my repair manual it say you should reset the O2 sensor (behind the speedo on an 89)--Doesn't tell how often and how to accomplish and how to accomplish the task. Ideas....

Thanks, Todd

That's just to reset the O2 sensor light on the dash, it only needs to be reset when the light comes on and stays on. Its just to advise you to change the sensor, it is a counter connected to the odometer and goes off at a set mileage.

I bought a Bosch sensor at Napa for $20 or so. It was the exact sensor (same part #) and I just cut the old wire and re-attached it to the new sensor.

it appears the po for my car had the catalytic converter removed. the replacement pipe does have the o2 sensor attached. does that imply now that the dme system will get confused now that the sensor is 'sensing' from a free flow pipe, and not a catalytic converter? just wondering about that.

I doubt it, Adam. The O2 sensor is in front of the CAT and the flow really be the same with or without the CAT, so I doubt if your O2 sensor is affected by the absence of the CAT.

with no CAT, you have the option of trying some non-O2 setups, which (without a CAT) I would consider to be safe. Indeed, the slightly rich mixture described above is how cars "like" to run. It is likely to result in cooler running, perhaps spunkier performance and likely greater longevity as well. Cars set up for emissions simply run "on the edge" lean. White spark plugs, etc.

As some of you may recall, I don't like taking 'combustion chamber' chances. This environment (in emission cars) is so hot that ANY misadjustment in the wrong direction (too lean or too advanced ignition) can melt expensive engine parts.

Adam, with your situation, I would probably be comfortable experimenting without the O2 sensor to achieve a less lean mixture. Be warned though, it would probably change your 'power band' noticeably and make your car funner to drive.

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'83 SC

I went to my local "Autozone" and inquired about a O2 sensor for my 911....$119?? What gives? Is there a different part number that doesn't use the word Porsche in it? I was thinking about replacing it but for $119 I'll just wait.

I used to work in a plant that manufactured o2 sensors.

Basically, they operate all the same. Most generate a 0.747 volt signal @ a 14.7 to 1 air to fuel ratio

The difference is in the number of wires.
One wire--just the signal wire

Two wires. Signal wire and a ground wire to the case.

Three wire. Signal wire and two wires for the internal heater.

Four wire. Signal wire, two wires for the heater and one wire for the ground. Note the ground for the singal is isolated from the grounded metal of the sensor.

IHMO, if I needed a 3 wire sensor, I would find a inexpensive 3 Bosch sensor and cut and spice (using solder and heat shrink) to the old connector. Make sure to use lots of anti sieze on the threads.



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Smoke Daddy