roccocaiazza

I have a 2009 911S and I drive it aggressively. I used to get about 15 miles/gallon but now about 12.9. I know it is hard to equate driving habits to gas mileage but it does seem like something is going on. No error codes and I have always used Costco premium gas. Might use a fuel injection cleaner on next tank of gas. Spark plugs have 30,000 miles (book recommends 40,000 for change). Car's performance has not suffered.

steveP911

Tire pressures too low? I get about 8 mpg on the track. You must be really aggressive or something is wrong.

jchapura

Do you have your used oil analyzed? What's your fuel dilution value? What oil are you running?

BHMav8r

Bad gas ?

Optionman1

I would be shocked if you drive more aggressively than I do and I was getting what i thought was poor mileage (17 mpg) until replacing all injectors and now seem to get over 20mpg without changing my driving habits. Agree with others, get UOA done. Good place to start looking for clues.

Bruce In Philly

2009 C2S 191K MT

15 is really low IMO even with a heavy foot... sounds like something going wrong for a long time. If the injectors aren't spraying appropriately, I suspect a Durametric should pick up some numbers somewhere that are a bit off... I just don't have the knowledge to help here. I would ask for help here as your are, and if no one here can tell you what to look for from the sensors, then I would find a good indy who knows engine management well to help diagnose the problem.

I found a piece on diagnosing DFI injectors here... more out there I suspect. I Googled "how to diagnose failing fuel injector direct injection".... read here: https://eeuroparts.com/blog/direct-f...hooting-guide/

My mileage has been amazingly consistent for years and years.



Peace
Bruce in Philly (now Atlanta)

workhurts

Does it have to be aggressive driving or a fault somewhere vs really short trips?

roccocaiazza

What is a UOA?

jchapura

Used oil analysis.

Optionman1

https://www.speediagnostix.com/

This is who I use for all my UOA, but others also use Blackstone

Kodos9865

Wow. I drive fairly aggressively on the street/canyons and get over 20 mpg. Definitely seems low in the teens.

How many miles are on this car?

evo9

Hello all,

2010 C2S 6MT here with ~ 53K miles

Fwiw - My combined city/hwy mpg is 16-19mpg according to onboard computer. I'd describe my driving style as old-guy fun (i.e.. not efficient), as I'm chill on city/secondary roads but, conditions permitting, like to wind her out on the hywy. Lots of 4th gear pulls to over the ton. Extremely slow/lazy lane changes when overtaking as not to draw unwanted attention to my velocity when hauling azz. My 30yr old son calls me the sneaky speeder. :-) I average one speeding violation every 4 years and I drive a lot. Imo - pretty good since I'm haul azz often. I give credit to Waze and continuous refinement of stealth hywy driving skills.

I assume I could get 19-22mpg if I practice self-restraint and set cruise-control at 60-68mph but, way too bland for me. Here in FL when I do use cruise-control, it's set at 80mph as a base to keep up with top 1/3 of the fastest traffic flow speed. Find myself dropping 2-gears and accelerating hard to leave folks who start following a little to close. My idea of a just a little bit of fun in this life.

Regards,

W

r_towle

I just saw a hilarious answer to this.

“This is a personal matter and we should not be asking these types of questions”