Unplug O2 Sensor and run richer?

[RJ Gilliam]

I upgraded my 86 930 last weekend with a k27 and muffler and intercooler. I asked people here for there input about getting the car "re-tuned" Most gave no clear cut answer so I made some calls

Well I have spoken to several people in the business, Don Jackson and Todd and they both say the same thing. Unplug the O2 sensor and change the system to run a little richer, about 3-3.5%.

They explained to me that the cars are "detuned" for them to pass smog and that they really need to run a litte richer so they dont detonate.

Does anyone have opinions?

[john walker's workshop]

that's what i do. even 4% CO smooths it out nicely.

[BlueSkyJaunte]

What about my NA '81 SC? Same thing? Still pings on occasion.

(PS: I don't know nothin', but can running too rich muck with the cat at all?)

[Rick Lee]

Yeah, and what about my NA 3.2? I have a cat by-pass on there too. Will running sans O2 sensor get too rich?

[BER]

Richard,

I run my 1984 with the O2 sensor plugged in. I adjust the mixture with my CO meter (approx. 3.5%) and the car runs pretty good. I am also using a cat by-pass pipe and Danske sport muffler.

Bruce
'84 Carrera
'77 911 (Euro spec)

[RJ Gilliam]

BER-- I thought about that, but according to the mechanics. that at higher RPMs the computer will lean it back out to 1%. So you defeating the purpose.

[stuttgart]

hey Fella's
I am going to cut another hole in my early exhaust to free the flow up a bit.. so i will need to richen it up abit after right!? and where can one get a co meter and where do you use it to get the desired results?


78SC

[Steve W]

Guys, on a n/a American 3.2, running with the O2 sensor unplugged will make your car run very rich and get you very poor gas mileage. European cars use a different chip which provide the proper a/f ratio without a O2 sensor. Using wideband exhaust analyzer to watch the changes in air/fuel ratios with and without it connected, and saw a/f ratios constantly running richer than 11:1 which is way too far from the ideal 14.5:1. The chip is originally programmed to pulse this rich for throttle acceleration enrichment, and expects within a second for the O2 sensor to sense the rich condition, and back it off to stoichiometric. With the O2 sensor connected, I noticed a extreme rich condition for a second whenever I made a quick, heavy, or even light stab at the throttle. This makes for the point that a steady throttle gets you the best fuel economy, along with a healthy O2 sensor.

[BER]

I wonder if running an aftermarket chip in the 3.2 motronic cars makes a difference in how the brain handles the mixture at high RPM's. I have a Autothority chip installed...hummm?

Bruce

[Steve W]

Bruce, actually it does. The O2 sensor has a certain window around the chip's preprogrammed injector timing for which it can adjust the mixture around. Beyond that window, the O2 sensor signal cannot adjust the mixture further. Your Autothority chip, for example, maps the fuel mixture richer at upper RPMs and at greater loads, so that when you floor the throttle, the fuel mixture goes full rich, and while the O2 sensor is telling the computer that it is running too rich, the the farthest back the computer will lean the a/f ratio out to is around 12.7:1, the ratio of maximum power. This is completely different from the full throttle fuel map, which is activated when a switch at the throttle body is activated when the throttle is full open.

[BER]

Steve,

That's very good information and very helpful. Thanks for posting.

Regards, Bruce

[Jack Olsen]

I disconnect mine on track days. I've never done any kind of side-by-side test with it, but I figure it can't hurt. (My 3.6 DME may be different than a 3.2's.)

[dad911]

Jack - I have been running my track car (3.6) without O2 sensor due to the fact that I don't have a 'bung' in the exhaust system for it yet. If you have the opportunity to do a comparison, please let me know.