[m9bm]

I noticed that i am getting less than 400 miles to the tank. After filling until the auto-shut off, I get about 350 miles before the fuel light comes on.
I drive about 8 miles to work and 8 miles back in stop and go traffic everyday. Some of it is at 50+ mph on the expressway.

The computer says I am getting about 20 mpg.

I'm worried I may have carbon build up.
I bought the car in 8/2013 and my mpg has steadily been dropping. I may be imagining it, but I feel like I've lost power as well.

Thoughts? Should I do preventative maintenance? Or just drive it until something goes wrong? I plan on keeping the car forever.
I have the Gold extended warranty until 2017/100k.
Mileage: 51k

[Hoooper]

someone who has experience getting it covered under warranty should comment on what to do, but I would suspect CBU.

[BB_cuda]

FWIW, I normally only get 20 mpg when doing my normal commute. I have one piece of it that is 45 mph. Especially since I got Ecotune out on and I'm gunning it now. I drove it on a road trip and got 39 mpg going 75.

Before you convince yourself of CBU, go drive it on freeway for a long while and get a legit fuel usage. Combo city and highway is a crapshoot unless you have a solid basis of comparison. Best of luck, either way

[GottaBeKD]

Keep in mind these are heavy cars. Stop and go really kills the economy and they thrive on the open roads.

I agree take it on a road trip and see the mileage.

[taibanl]

Have dealer run a test plan on the injectors

[skychismo]

They might not cover anything under warranty until you throw a code. I threw an SES light for swirl flap malf and they ended up replacing the intake and walnut blasting the head under warranty for CBU.

[dixy2k]

diesel are not known for good fuel economy in heavy or city traffic.

[AzureHaze]

I'm lucky if I can get past the 400-mile mark with my commute! Even though I use the manual shift mode (to avoid throttle lag) 100% of the time during bumper-to-bumper traffic, I don't think switching to D mode makes a huge difference to my mileage.

[grzes]

I would suggest to get the Gas Tracker app, build your data on the fuel consumption, I have been using it for 3 months now and slowly starting to see that monitoring is getting better. I had carbon clean up done on my car and honestly gas mileage did not improve at all, if anything it got little worse as I can't get the numbers as they used to be, not a lot but still consumption went up (I drive lots of highways so it is easy to monitor).
Before carbon clean up done
Highway (plus 3 to 4 days city driving till tank was empty) - 5.9 - 6.6 l/100 km
City only - 8.7 - 9.5 l/100 km
After carbon clean up done
Highway (plus 3 to 4 days city till tank was empty) - 6.3 - 6.9 l/100 km
City only - 9.2 - 9.9 l/100 km
Sorry, wish the app would help me converting this into the MPG but I can't figure it out lol

[m9bm]

I also did one all highway trip. I couldn't break 500. I got 450 miles. I used cruise control almost the entire way at 80 mph. Computer read 28-29 mpg (I reset it before making the trip.)

Since I can't get anywhere near the 36 mpg number I'm now concerned. I guess I'll wait until a code is thrown.

[Mark M]

As FYI, pleased to report I got a hand calculated 35.72 mpg yesterday over 551.6 miles on the tank with computer indicating another 34 miles remaining. Car was used for a 120 mile highway trip plus my normal 75 mile daily commuting.

Carbon cleanup was done 11k miles ago and ever since the EGR has been blocked off.

[m9bm]

I need to get carbon cleaning then!!

I can't even break 500 on all highway, all cruise control, and no A/C!!!

[ptpending]

check your thermostats

[m9bm]

Sorry but how do I do that?

[taibanl]

Originally Posted by taibanl

Have dealer run a test plan on the injectors

This is why: (click for full thread)....

Originally Posted by austinla335d

Got it back with 6 new injectors. I'll report on mpg soon.

Originally Posted by austinla335d

He said there was no SES, but when he static tested or something like that, he found them to be "faulty". Replaced all six.

I'm averaging 30-32 with 50/50 driving, shifting with paddles in DS as per usual. Certainly a 7-9 mpg increase deserves credibility on the injector swap, but not sure how it was ever approved.

Originally Posted by austinla335d

All you really need is the following statement:
"Customer states fuel consumption is poor, progressively lower. Customer authorizes XXXXXXX to test drive car for diagnosis.
Installed 13 53 7 808 089 :B1SA-Injector Qty:6
Connected battery charger and performed short test, found no faults in DDE.
Checked engine sensor values for any abnormalities. Found fuel injector quantity adaptation values excessively high. Ran injector test plan, found injectors faulty. Replaced all 6 injectors, performed calibrations, reset adaptations and road tested OK. No other faults found"

It was a $3,800 job according to my SA.

[m9bm]

Thanks for the input.

I'll ask the dealer to "run a test plan on the injectors".

[diaz92376]

I think that's normal considering your commute. I always got 21.5 since I bought the car and even after the carbon cleaning, I also do mostly city.

[Got_Diesel]

Our cars are rated at 23 city, 36 highway and 27-29 combined.

23x16.5 = 379.5 mile range
36x16.5 = 594 mile range

27-29mpg = 445.5 - 478.5

Varies a lot.

[grzes]

Originally Posted by Got_Diesel

Our cars are rated at 23 city, 36 highway and 27-29 combined.

23x16.5 = 379.5 mile range
36x16.5 = 594 mile range

27-29mpg = 445.5 - 478.5

Varies a lot.

thx for the numbers, I have run the calculations of converting and it seams I am pretty close to the numbers you have posted which I bet are at the ideal conditions. If I take into the consideration the wind and the road and speed I don't think I have anything to complain about

[skychismo]

I'm CBU free after repairs, and I can pull over 40 MPGs on the highway if I try, 36 if I don't. My wife uses the car daily for very short drives. She lets it idle in the driveway for 5 minutes before getting in in order to let the AC cool the car down, and still gets 24 MPGs and she flogs it. I can get 30-32 city driving if I try, 24 if I flog it.

[m9bm]

I can't get anywhere near that mpg even with all highway. This makes me think something is wrong. All highway I can only get 28-29 MPG..

[taibanl]

Originally Posted by m9bm

I can't get anywhere near that mpg even with all highway. This makes me think something is wrong. All highway I can only get 28-29 MPG..

Im the same way-ABSOLUTE BEST i can get is like 34, and that is hypermiling on ramp to offramp all interstate