If your car is running fine with the o2 sensor in the circuit then disconnecting it will allow the car to run richer and less miles per gallon. It is a trade off. In my opinion cars that have problems with the CIS and disconnect the O2 sensor just mask the problem and don't solve it. Hey I might be wrong but that is just my opinion. Enough of my $0.02

Hit one of the better Porsche specialist shops in Denver to get your CIS adjusted right. Storz, Eurosport (there are two good ones with this name), Eisenbuds or the P dealer in Lakewood--> Prestige. You lose 20% of your hp here in the Mile High City. That said, there are some very fast SCs in town, join PCA/RMR and meet these owners.

Bill, if the car is adjusted right for the altitude, you get the 20 ponies back, right?

You'll get some of them back, not all. Only when you get back to sea level do they all return, provided you get the mixture set right.

Joe

Richard Leshander,

What do you mean your engine blew running too rich? Is the mixture check somthing I can do or do you need some special equip. for this job.

Thanks, Rick

As said, when you return to sea level, the hp loss is rectified. That is why turbocharged cars are so popular to gear heads in high alitude locations, they make their own atmosphere @ the manifold.
My 5 cylinder, '95 S6 Avant blows the V8-10 SUV doors off going up the mts for skiing, but that does not get those slugs out the left lane though...
Hey I get bad mpg in my 2.4S MFI engine too and there is no real magic adjustment there on that beast.

I was thinking the same question Silveresrty911S. I've never heard of anybody blowing their engine due to having it run too rich. Usually that resultes in poor mileage, sometimes black smoke, and more soot in my tailpipe. But that's the first time I've heard of it ruining an engine. Now I have heard of valves getting fried due to a lean mixture.

If you let it go long enough, the gas will dilute the oil and kill the rings and maybe cylinder walls too. It also makes the engine run too cool and it's hard to get up to operating temp. I let it go too long, while trying certain fixes and then driving a 1000 miles to measure oil usage, which kept going up. After about 4k-5k miles, my rings were shot and I was getting all kinds of smoke.

BTW, I think the ultimate culprit was either a bad head temp sensor or bad AFM.

Don't forget your valve guides take a beating with over rich mixtures too. Seems that was one of BA's observations on rich running Carrera's.

Joe

I guess that would explain the big puffs of smoke I got when I shifted at high revs.:(

Keep your o2 sensor plugged in for fuel economy. It keeps the fuel air ratio near stoich. 14.7:1 average, by hunting for full rich to full lean several times a second. Now, keep in mind that under WOT, the 02 sensor is ignored in open loop mode, and the mixure will run in the 13:1 range. (good for hp, bad for economy, but good for engine health under load)
Altitude will not effect gas mileage as the fuel air metering system can more than handle the 20% less air density at 5000feet. most newer cars have even barametric sensors and temp sensors that even more finely refine their capabilities. generally, with no help, the AFM can adjust and keep mixture correct up to 7,000 feet. (28% less air density.)

so, in a nut shell, use the 02 sensor, even if you race, there is no down side for using it as it came from the factory. for fine tuning mixture, there is a mixture screw for basically idle and criuse conditions on the AFM and CIS models. MAF, no adjustments are usually found.

MK

No, mixture should not be effected by altitude up to 7k feet.

try 20% not 20 ponies if you could find the density equal to sea level when at 5000feet. (got boost?)

Mk

Don't feel bad. I'm getting 6mpg. in the city and am looking for any possible reasons why.

I've seen NO ill effects to having the o2 sensor hooked up for the past 2 weeks. And with the weather warming up, it appears that my gas mileage is improving. So far this tank I've traveled 160 miles and used 1.5 quarters of gas leaving me to believe that I SHOULD get 300+ (hoping for a big +) on this tankful. Techron is bought and getting added soon :)

thats pretty bad, considering we get that at the race track, full throttle for an hour!!!

you may have a gas leak. even running rich, wont give you that bad of mileage, unless you are seriously washing down cylinders!!!

9:1 air fuel ratio could do this, but it would be dripping rich!!
check the plugs and exhaust pipe for some real wet stuff.

mk

18/27 MPG!
 

My 1980 SC coupe (just turned over 100k miles!) regularly gets 17-18 mpg in town and 25-27 mpg on the interstate. On one trip that was traffic controlled at a steady 65 mph, I saw almost 30 mpg. Since you are in Colorado (probably at a high altitude), you should be able to lean out the fuel mixture to get better mileage and better performance. Remember, the 4 cycle internal combustion engine likes to run close to 14:1 air to fuel ratio. An exhaust gas analyzer (available for around $125.00) should tell
you if the FI is running rich and allow you to make your own adjustments.

Good Luck!

Fred Cook

Yes, we have seen 22mph out of our 400hp 928 race car when we drive it to the track!!!. still uses the stock injection and MAF systems. ideally, the 02 sensors will keep things around 14.7:1 fuel to air. the off the shelf air fuel meters are really only ball park meters. however, they will give you an indication of things when they are really wrong. (like, the full thottle microswitch is not connected, or the o2 sensor is really bad or disconnnected, etc)

MK