CO/O2 Guru's
 

As I have stated before, I have a 1986 930 that I have removed all smog equipment, and replaced the cat and muffler with an early 80's euro. (Single pipe, I never liked the dual pipe). I just basically wanted to get rid of all the heat that the cat generates and the smog equip to make servicing easier. I don't track the car, and for right now not going to make any other changes/enhancements. I always run prem fuel. My questions are for the effect of the O2 sensor and CO adjustment. I currently have the O2 disconnected and the CO at 2%. I'd like to know the pros and cons of:
1)Setting the CO back to specs .6 +- .2 and reconnecting the O2
2) Leaving the O2 disconnected and increasing the CO to 3-4% per recomendations from this board.

What effect does the O2 have on setting the CO?

The sensor will try to get your car to run at 0%, that is Stoich. All fuel will be burnt, emmisions will be low, fuel economy good.
The bad news is that our cars like a richer mixture for cooling to preserve the engine... Have you seen pics of pistons eaten by detonation ?

In theory, as long as I don't have detonation, I should not suffer any damage from setting the CO to spec and connecting the O2 ? The reason I am asking is I use this car for long trips (highway) and I'd like to set it to spec for the trips, (gas mileage) then when I am home fatten the CO and disconnect the O2, as that is when I would do more spirited driving.

Fit a wideband AFR gauge, then you will know what is going on. You cannot hear damaging detonation. Something like the Innovate LM1.

Nathan, Thanks for the consistent replies. I find it hard to believe that setting the CO to spec and running the O2 could possibly damage a stock engine. Going leave the O2 disconnected for now and play with the CO between 2-4% to see where it runs best. I'd really like to be able to run stock specs on trips though, for the mileage....Been looking at the LM-1's may follow that route to really be able to see what it is actually doing. Thanks again for all the help...

Tim.

Can I connect a digital multimeter to the O2 sensor, get a voltage reading then convert to a CO %? Where would I get the conversion table?

If your car is stock then running with sensor connected should be fine. Checking the AFR's is your answer for peace of mind.

The stock sensor is a narrow band and only good for measuring 0% (stoich). Our engines need approx. 4% at full boost or 12-1 AFR. The stock sensor is not accurate at checking this. Get a wideband setup fitted !

Tim, what affect has removing cat +stock muffler made? I have an 88 stock that I am considering doing the same vs a test pipe. Any comments? By the way I have a place on IOP, do you do your on wrench or do you use someone in Charleston?

Brett - Sent you a PM...

Nathan - What are your thoughts on connecting the O2 (for normal highway driving) and setting the CO fat for when the car is on boost and the O2 is taken out of the loop?

I'm going to take your advice on the LM-1....

tim.

Regarding the VOM as a monitor on a narroew band O2 sensor; it can be done. I experimented with this years ago on a fuel injected 914. I discovered the maximum power was acheived @ .945 to .985 volts. I had a real-time adjustment in the car. I could set the O2 @ .500 (stoich) and the power was noticably reduced but great milage for the long haul. If I increased the mixture to above .985 the power would again drop off due to over-rich condition. The maximum output voltage of a narrow band 02 is 1.000 volt by design, my Fluke 77 would register 1.006. That's reasonably close. I don't know how the output voltage relates to A/F ratio but I couldn't argue with the seat-of-the-pants real-time test results. Also, be sure the circuit loading is minimal on your test meter. I believe it's at least 100K per volt on the Fluke. An inexpensive meter will not work.

When the AFR is producing maximum power on boost it can be damaging our engines. We need to go slightly richer. For a NA car it would be fine. At cruise we do not need 12-1 we can go leaner.

Tim, not sure how that would work. Possibly it would spend too much time trying to fight each other and it wouldn't be good for anything.