Hey folks. The wife and i finally just fulfilled the 13 year dream of owning a hi-perf sports car when we bought a '07 Cayman S manual trans, Carmon(a) Red, with under 27K miles on it. We got it in June. So we are walking on air, and its performance seems breathtaking. But i am looking for your opinions on the relationship between possible bad O2 sensor (or Cat) and the fuel economy we are experiencing so far. Some background:
It's her daily driver most days. I have put fewer miles on it than the wife, and mostly on the weekends. We both agree I drive it more spiritedly than she does, although we both make a point to keep the revs north of 2500 under load, but rarely and only briefly >5K. Most miles are logged at 2500-4000 RPM. The only modification we know of is the Borla Exhaust. It has had maybe four tanks of 93 octane fuel put through it since we got it in June, with a combination of 80% highway miles (at between 50 and 75 mph), and 20% in town. Let me make clear we did not buy it for fuel economy, but! Given the published ratings and internet sites which track real-life fuel economy by make/model for the 3.4 flat six, i would have expected to see between 20 and 26 MPG given our driving patterns. Instead we seeing 15-19 MPG using trip odometer and calculator. Makes me wonder if is indicative of a fuel or ignition system problem.
After about 150 miles, the check engine light came on and i pulled the code P0421 which indicates bank 1 c/c not operating within limits. I am aware the previous (and original) owner had an O2 sensor replaced last summer - not sure which side. For what it is worth, the owner of the shop who maintained the car for the past couple of years expressed the opinion that the previous owner, a pediatrician, likely drove it more gently than the mfr intended, and suggested an 'Italian tune up' might help! My belief is a bad O2 sensor could create the code that c/c is not operating properly. Agreed? I plan to swap sides on O2 sensors, clear code, and see if code switches banks, before buying a new O2 sensor.
Wondering what is the likelihood the a c/c needs replacing on such a low-mileage nine year old CS?
Anyway, feel free to weigh in on any of that. But in particular, do you agree a bad O2 sensor is likely to account for the mpg we are seeing?
Thanks for your input.
For a 987 driven as you say (moderate throttle, 80% hwy), you should definitely be seeing mileage over 20 mpg.
You are on the right track with swapping the O2 sensors. Start there and see if the codes change.
It is possible that the cat has gone bad, but seems unlikely for such a low-mileage car. Also, a clogged cat could cause lower mpg, bit it would also affect power, so I think you would have felt it.
If you drive in heavy traffic you will get fuel economy in the teens. I drive rural roads and get 23.
I have had an O2 sensor go bad on my Chevy 2 times. It doubled fuel consumption both times.
If he bought it with a bad or failing cat, he would not know it because he had no reference of what the power should have been.
A Dr. that drove it like like a baby, could certainly have ruined the cat.
Thanks for the input folks. Guess i will hang in there until next oil change at which time will flip O2 sensors and see if that flips the code to Bank 2. I anticipate replacing an sensor WAY less than replacing a cat.
