[frank08335xi]

Hello everyone i have an 08 335xi with the n54 engine. My car for the past month has been burning insane amounts of gas.i only get 190-210 miles with a full tank and normal driving. It doesn't need a tune up. It doesn't leak gas. And the check engine light is not on. Any ideas on what could be causing this issue. Thanks

[Cloud9blue]

anything from bad o2 to a leaking injector... we can't really help anymore than that without a log or some sort...

[335NJ]

How old are your spark plugs? When was the last walnut blast service on the valves? If you have a tune or some sort, maybe do a datalog and check the AFR to see if it's running rich?

Winter blend fuel naturally causes a drop in MPG too btw.

[frank08335xi]

Spark plugs have 10-15k miles on them. What is a walnut blast service? Ive never heard of it.

[Bigboost_E92]

http://www.maperformance.com/blog/wa...-335i-e90-n54/

[kseyfi86]

Do you do mostly city driving? E85?

[Jeff@TopGearSolutions]

Originally Posted by frank08335xi

Spark plugs have 10-15k miles on them. What is a walnut blast service? Ive never heard of it.

It's cleaning of the intake valves. They are prone to gunking up with carbon, resulting in less horsepower, lower throttle response, lower gas mileage, stumbling idle and even misfires.

Usually after 35,000 miles they are significantly gunked up where there is an obvious improvement after they are cleaned.

[frank08335xi]

yea city driving

[335NJ]

Originally Posted by frank08335xi

yea city driving

How many miles on the car? And how many have you personally put on it?

My guess is you're way past due for a Walnut Blast. Especially city driving, idling or low throttle a lot is an easy way to gunk the valves up with carbon, since there's not many times where the revs are up high to help blow some of it out.

One of the best $300 i've spent on this car.

[MTTH]

That's what I average with my car (2011 N52 328i xDrive) & I still don't know if it's normal or not. Spark plugs & coils were changed in January.

[Tiago@VRSF]

Does the car stumble at startup/idle when you turn it on in the morning after it's been sitting for a while?

I'd second the gunked up valves but leaky injectors can blow through gas pretty quick. Have you noticed any more black smoke than usual?

[jonas]

You can always check your MPG readings with normal driving and make notes of the numbers if you don't have a tuner. That will give you something to start with. Also, just because there is no check engine light does not mean there is no problem. The computer stores all kinds of codes that won't trip a light.

[donR]

I have a similar problem, no error codes, recent walnut blast but only get maybe 180 miles between fills.

Our average speed is around 14mph due to all short trips so I thought that might have something to do with it.

Anyone know what sort of mileage I should get at that average speed?

[Izero]

at 14mph you won't get very high fuel economy... things I would check (in no particular order):

1) MAF Sensor - Clean with special MAF Cleaner if dirty
2) Throttle Body - Clean if coated with grime/oil
3) Brakes for dragging during normal acceleration/driving.
4) Tire Pressures (would cause minimal impact but some impact nonetheless)
5) Intake Valves - Get walnut blast service done if dirty
6) Wastegates for stuck at full open
7) Spark Plugs - Replace if gap is too large or excess build-up present [this will also indicate if an excessively "Rich" situation is present for each cylinder.]
8) Oxygen Sensors - Datalog during normal driving and 1 or 2 WOT pulls & post up on here.
9) Injectors - might be leaking
10) EVAP system - this requires special tools but could be a problem (would throw CEL though)
11) Make sure no one is maliciously siphoning your fuel. (common if you're in urban area and park on street)


That is where I would start, if all of those come up empty then I'd definitely try using a different gas station, I've seen some shady stations fill their tanks with lower grade fuel and sell it as higher grade (illegal yes).

I'd really think about checking the Wastegate Duty Cycles because if they are wide open all the time those turbos are going to be constantly spinning which will require more fuel.

we would really need to know more about your vehicle to address anything further, if you have any Modifications, Mileage, Transmission type, recent maintenance performed, etc. etc.

[pinky_and_me]

I am in the same boat but I'm pretty sure mine is because I haven't changed the oil recently. I've noticed that on my car that's the primary reason for increased gas consumption.
Before spending lots of money on injectors and o2 sensors try changing your oil.

[Rotary Rasp]

If you only driving in the city, 200 miles per tank isn't that uncommon. That's what I normally get, but I do run 50% E85.

[Jeff@TopGearSolutions]

This car gets pretty bad city mileage however I noticed when on stock run flats it was important to maintain correct tire pressure.

I noticed several times that my stock run flats would lose tire pressure over time and I only noticed when my MPG decreased significantly.

Otherwise, it could just be your right foot.

If you are entering boost a lot during city driving it's going to eat tons of gas.

[ferocity02]

The OP is talking about MPG's <11, which is indicative of a mechanical problem. Low tire pressure, carbon buildup, or running E85 won't cause MPG's this bad unless he has these issues and has a VERY heavy right foot in city traffic.

[kseyfi86]

I saw my MPG drop down to 14 when I lived in the city right next to my work. When I moved further away it crept back up to 19ish.

[E30 Racer]

Originally Posted by Tiago@VRSF

Does the car stumble at startup/idle when you turn it on in the morning after it's been sitting for a while?

What are these symptoms indicative of?

[j1gilles]

+1 for multiple leaking injectors

[buylongterm]

My car gets roughly 14-16mpg but i attest that to city driving, very aggressive driving and the mods on my car.