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Owned mine for 17 months and have really only used it for very high revving canyon drives once a week or every two weeks. About 80 miles round trip. I dare say I've never calculated the MPG. And probably shouldn't But I do have to get gas pretty much before each drive up
A good friend of mine and a Rennlister here told me his 4.0 FSI got 34 MPG on a cross country trip recently...That's pretty impressive...
I have specialized in engine management even before fuel injection and emission controls were mainstream, and I can tell you that with modern cars 95% of the time when fuel mileage is a real concern ( and no fault codes) the 02 Sensors are responsible for the wasted fuel...Their main job is to monitor and help control fuel mixtures. They used to be mandated to last 80k miles, with the reduction of ZDDP they were hoping for 120K miles , but they often get lazy way before this...
Is there a specific measurement or test for the O2 sensors?
You did not buy the Porsche for its fuel economy, did you?
I don't know what specific mpg numbers OP is getting, but when it's approaching single digits there's clearly an issue going on with the car. This shouldn't be ignored.
Might be worth it for the OP (and others with poor mileage) to try Redline SI-1 Fuel System cleaner -- the references to it in the DI40 thread makes it sound like it walks on water and is better than Techron and others (based upon what's it contains). The posts discussing it start here (https://rennlist.com/forums/996-foru...l#post19181932) -- there are only a few posts on the fuel cleaner, since it's an oil thread), but it sounds quite good. I've used Techron and Sea Foam in the past, but am going to give Redline SI-1 a try based upon the comments.
thanks Glenn, I can't add any more to the subject than I did in that thread, unfortuantly many will read it and not believe it, or it will go over their head. I'll just recap by saying that the 02 Sensors are the judge/jury/and executioner of fuel mixtures when at "closed loop cruising" for MPG...
It seems that most people will change plugs and coils as a first start to MPG concerns even when no missfires are recorded...Even though plugs and coils also age as time and mileage passes,( plugs will wear and collect carbon deposits and coils will develope small cracks) but if they don't missfire they don't effect MPG...If someone were trying to be "thrifty" and were merely concerned with MPG, the money would be better spent on upstream 02 Sensors..
thanks Glenn, I can't add any more to the subject than I did in that thread, unfortuantly many will read it and not believe it, or it will go over their head. I'll just recap by saying that the 02 Sensors are the judge/jury/and executioner of fuel mixtures when at "closed loop cruising" for MPG...
It seems that most people will change plugs and coils as a first start to MPG concerns even when no missfires are recorded...Even though plugs and coils also age as time and mileage passes,( plugs will wear and collect carbon deposits and coils will develope small cracks) but if they don't missfire they don't effect MPG...If someone were trying to be "thrifty" and were merely concerned with MPG, the money would be better spent on upstream 02 Sensors..
Thanks for the info. It looks like there are a total of four O2 sensors -- pre-cat and post-cat on each side. Do all four need to be replaced, and is OEM better than the Bosch equivalent?
I am the Renn lister with he 996.2 that Skip referred to in post 12. My car has a 4.0 FSI Stage II+ engine. It is the m9Experience engine that I worked with Jake Raby to build. My wife and I actually went to Jake’s Skunkworks facility last July and assembled the engine with Jake coaching us. We installed the engine, ran it for 1900 miles to break it in and then drove it to Rennsport Reunion at Laguna Seca last September. After Rennsport, we drove up the coast to Seattle and then back across the northern US. We drove approx 9200 miles total and averaged 30 mpg for the trip. We drove. 400 mile + stretch across Wyoming and South Dakota at 85 mph and got 34 mpg. Photo of trip computer attached. It is a very nice engine!
Mark
Might be worth it for the OP (and others with poor mileage) to try Redline SI-1 Fuel System cleaner -- the references to it in the DI40 thread makes it sound like it walks on water and is better than Techron and others (based upon what's it contains). The posts discussing it start here (https://rennlist.com/forums/996-foru...l#post19181932) -- there are only a few posts on the fuel cleaner, since it's an oil thread), but it sounds quite good. I've used Techron and Sea Foam in the past, but am going to give Redline SI-1 a try based upon the comments.
Originally Posted by theprf
My guy that cleans fuel injectors (hurst injector service) swears by the SL-1 cleaner, says none of the others are worth anything.
I doubt the injector cleaner will help, it's much more likely to be a MAF or an O2 sensor problem.
This. I've used this product numerous times and not only did it help produce some very low fuel contamination numbers in my UOA but also cleaned out a lot of the carbon build up from the tops of the pistons. Nothing else produced the same results. I've posted photos from a borescope in one of the threads. I accredit it to helping me find some piston damage that led to an engine rebuild. With a piston coated in black carbon I wouldn't have found it.
04-29-2024, 02:53 AM
But I do have to get gas pretty much before each drive up 
