Running hot w/ O2 sensor connected, normal?

[scmguru]

Getting ready to register and go through a smog test on a 930/68 in Cali.

New O2 sensor, idle set to 900, duty cycle verified between 48-52%, narrow band A/F says I'm right where I should be at idle, cruise etc..

Power is fine, no hesitation, surging etc.. but the car seems to be running about 20% warmer per the oil temp gauge w/ the O2 sensor connected vs. disconnected. (ie indicator at 9 or 10 vs. 8 o clock)

Is this normal?

Thanks.

Mike

[Walter_Middie]

Mike,

A turbo is not an engine that should run lean, and running too hot is a symptom of either running lean or having too much advance. At 48 to 52% (I assume that is when hot) you are at the high end of running lean. It has been said on here to set it around 30-40, because some have found the WOT mixture too lean on many of these engines. I'd double check your advance at several RPM (not just idle) first, then if that is OK, back off on the mixture so that it is running a little richer. See where that gets you.

[scmguru]

Advance/timing checks out fine (per the workshop manual) at idle & @ 4000RPM.

Re: Duty-- 48-52% when fully warmed up.

Please forgive my newbie question, If I set the A/F mixture to richer (duty of 30-40), doesn't the Lambda computer just lean the mixture back out by raising CP and get me to the same point of 14.7 A/f?

In any event, I'll give it a shot and report back! Thanks.

Mike

[Walter_Middie]

If I set the A/F mixture to richer (duty of 30-40), doesn't the Lambda computer just lean the mixture back out by raising CP and get me to the same point of 14.7 A/f?

In a sense, yes - when you set the mixture on this system, you are really only altering the open loop mixture (cold and WOT), the system corrects the mixture back within the range.

[scmguru]

Solved..

I finally tracked down the cause of ALL the issues I've been having w/ heat (and boost) on our '86 930.. a plugged up/broken original catalytic converter.

Symptoms:

* Boost delivery was inconsistend and frequently wouldn't reach .8Bar, even with the MBC turned all the way up.
* WUR cold control pressure had to be dropped to richen up mixture and the car would still only idle @ 500RPM until it warmed up.
* A/f had to be set rich or idle was terrible
* Car started running about 20% warmer than normal
* Boost gauge connected to booster hose was showing 30% or more LESS boost than the gauge connected to the wastegate line (Vac was OK though)

I had a new catalytic converter installed, reset the air/fuel mixture and all my boost problems, low boost, lag, heat - disappeared.