Could my SC have been running hot because. . . . .

[Gogar]

My oxygen sensor has failed or just isn't making a connection?

Last summer, My SC was HOT HOT HOT all the time, it seemed.

This is too hot, right?

I was fiddling around with mixture settings yesterday; for fun, and because I don't have a cat anymore, and it's a little easier to jam the sniffer in there.

When I got the car, my mechanic set my CO to .5% (oxygen sensor unhooked), which is with in the spec provided by the Haynes manual, etc., if you want to USE the oxygen sensor. GREAT.

So, please educate me if I'm wrong but here's my guess.

As I understand it, when you hook the oxygen sensor back up after setting the CO%, the computer will enrich the mixture when necessary, right? Most of the time, actually, if you set your starting CO to .5%, right?

So, the connector on my oxygen sensor (like most SC owners) is broken, and is it possible that even though it LOOKED like it was hooked up, maybe it wasn't? And I've been driving around REALLY REALLY lean (like, open loop, .5%) for some time?

And really really HOT, because of the lean condition?

Whatcha think?

Thanks

[psalt]

No, your oil temperature problem has nothing to do with the O2 sensor. A CO of 0.5% is a 14.27 AFR, which is slightly rich, and will not cause a temperature problem at light cruise load. If the lambda system is broken, with an inoperative FV, that is another story. I would concentrate on the cooling system, remove the alternator/fan inspect the blades, clean out the fins, oil cooler, make sure the fan belt is correct and adjusted properly, make sure the thermostats are working and the front cooler is hot. Make sure your heater plumbing is intact. If you still have the vacuum retard on the distributor connected, plug the line, reset the ignition timing to 7 degrees BTDC, and reset the idle speed to 950 rpm. The vacuum retard causes a heat build up at idle, but should not effect cruise temperatures. Lubricate the distributor and check the high speed advance with a light. Connect an analog dwell meter to the lambda test port and adjust the mixture to 30-40 dwell. These are the optimum settings for your model.

[Gogar]

Thanks, Paul. I'm familiar with all the 'usual suspects' to check about the temp. This is just me trying to understand some (other) things about o2 sensor, lambda, and mixture stuff, so that's helpful.

If you say a CO of .5% is "slightly rich", then tell me your theory on why everyone loves to unhook their oxygen sensor and set their CO at 3.5%. I always thought a higher CO% meant richer. Because, when I turn the mixture adjustment screw clockwise (righty richy), the CO goes UP.


If I set my mixture to .5% CO and leave the o2 sensor disconnected, what would be the overall mixture condition of my fuel?

I'm guessing REALLY LEAN, if lots of people are disconnecting their o2 sensors on purpose and setting to 3.5%CO.

Thanks

[equality72521]

I can't answer your questions but I DO know that when I was running lean the engine ran WAY hot. Set the mixture correctly and I'm as cool as Jack Nicholson now

[john walker's workshop]

the somewhat richer idle setting really doesn't affect the mixture at higher rpm. it just smooths out the idle and helps a bit when you accelerate from a stop. the rest is pretty much pre-determined in the fuel distributor.

[psalt]

If you say a CO of .5% is "slightly rich", then tell me your theory on why everyone loves to unhook their oxygen sensor and set their CO at 3.5%. I always thought a higher CO% meant richer.

No theory involved. 14.7:1 is stoich, anything lower is rich, not lean. The fuel mixture with CIS is determined by the height of the air flow sensor and varies at different rpm. The fuel curve with CIS is determine by the shape of the air flow sensor funnel and the vacuum of the engine, not the idle setting. CIS engines like richer mixtures as they age and develop vacuum leaks and lose compression. Your system has the ability to have decent emissions and mileage , with the proper AFR for WOT. My advice is to read the Bosch manual so that you understand how the CIS lambda system works, then find out if you engine is working as designed. The O2 sensor is there for the health of the cat. No fuel management system can maintain a steady stoich, so they dither the mixture rich and lean to keep the cat working properly. The system goes open loop at 35% throttle and the O2 sensor is irrelevent at that point.

[Gogar]

That's awesome. Thank you guys. That's helping me understand a bit better.

[slodave]

Hi Jermey,

Check this link. Yeah, the sensor is connected for the test...
911SC Oxygen Sensor
O2 Sensor functioning? Paranoia?

Dave