To use O2 sensor or not... 82SC

[CMXI-SC]

Guys,
I've been playing with my AFR/CO mixture and want some opinions as to the benefits/constraints of using the O2 sensor as opposed to not using it and manually setting AFR/CO. All conversation is appreciated.

[psalt]

Heelo Jack,

The first thing to understand is that the O2 sensor is ignored by the CIS lambda system during cold start, warm up and past 35% throttle. Disconnecting the sensor cannot improve performance. Leaving it connected and optimizing the tune up will give you the best combination of performance and mileage. My advice is to set the mixture to 30-40 dwell using the test connector (or around 13:1 AFR at WOT under load), disconnect and plug the vacuum retard line at the back of the distributor, and reset the timing using as much advance as your fuel quality will allow. The US 82 911SC was detuned to run on the factory specified 87 CLC fuel and 25 BTDC is not the optimum advance for the engine.

[CMXI-SC]

Thanks for the input Paul. What would the 13.1 AFR equate to as a CO%?

[psalt]

Hello Jack,

I am referring to the AFR under load, not an idle setting. The benefit of CIS lambda with the O2 sensor connected, is that you can tune for the best WOT setting and the system will pull back the idle and cruise setting to stoich. A 13:1 AFR is around 3.9% CO, but there is no fixed relationship between idle and WOT CO%. You want to measure AFR under load when it matters, CO% at idle is an emission test spec. and your car should be 0.4-0.8 CO% at idle in front of the cat.

[don gilbert]

good info Paul, Jack, what most don't seem to understand, once you go past the 35 degree throttle switch, the 02 system goes into "open loop" , which means it is not controlling the mix. Your frequency valve goes to a 90 % duty cycle to en-richen the wot mix. The 02 system has NO control once past the 35 degree switch, so how can that hurt performance? Leaving it hooked up will get you 25+ mpg, lower emmisions, and make you engine last longer. Plus, the beauty of an 02 car (80-83) as Paul said, is being able to make afr adj. past the 35 degree switch, and put the timing where its supposed to be ( i run 33 max with 93 octane shell) and still get great gas mileage at idle and part throttle.

[CMXI-SC]

Great discussion Paul and Don. Going to the garage now to re-connect the O2 sensor then take a spin. Driving to Colo next week for a little golf and fishing and mountain roads. Should be a good shakedown for the re-connect.

Thanks guys,
Jack

[GothingNC]

Why disconnect the 02 Sensor

why disconnect the O2 sensor?

[CMXI-SC]

John D.
Doesn't appear there is a good reason to disconnect based on the above discussion.

[GothingNC]

It's up to personal preference of the owner.

I have been running mine with the 02 disconnected for the past couple of years with no ill effect.