Help! E90 335i Auto (N54) absurd fuel consumption

[Zound]

Hi Fanatics and calling all N54 experts,

I'm working on a friend's 2007 E90 335i Sport auto and one of the issues I have been trying to tend to is the extremely poor fuel consumption.

He initially came to me with an issue of "low boost pressure" fault code which we solved by replacing the cracked charge pipe with an aftermarket COBB unit. Subsequently, I have done an oil service for him and will be installing a new battery soon.

The car has 135 000 Km's and besides the COBB charge pipe, is completely stock. I have run diagnostics and fault code reading multiple times but the car comes up clean.

The car is averaging between 25 and 30 Litres per 100km's. Yes, you read that correctly.

He has owned the car for just over a year now and upon purchasing the vehicle the average fuel consumption was indicated as approximately 16 litres per 100km's.

The car is driven spiritly but nothing unexpected of an x35 car. The distances he travels daily are very short, often less than 10km.

The question is, am I correct in believing this is unacceptably poor fuel consumption and there could/should be an underlying issue with the car?

 

[M3_devil]

Hi

Thats madness. My 335 around town stock was max 12l per 100km. Modded it was lighter.

At that kilos a carbon clean is on cards. Check advertiser section for carbon doctor.

Did you try and reset trip computer for consumption and average speed and take a trip on freeway to determine consjmption at 120km/h. Could be you friend sitting in traffic the whole10kms.

Would also recommend getting bt cable so you can log O2 sensor & map readings. Possible that they reporting faulty values to dme.

But start with carbon clean first

 

[Kish2604]

There is only 1 thing to be done to correct that fuel consumption and that's a carbon clean... All his driving behavior with the car points to oil that does not get hot enough and short distances over recent times. Add to that 135k kms that car must be so coked up I am surprised it still idles...

Pull the intake manifold yourself and have a look down the ports to confirm my diagnosis and make the decision yourself on what to do from there.

Ps. My ex 335i was cleaned by George Smooths carbon doctor when I got the car and it had +-115k at the time. The ports were horrendous... If you search the carbon doctor subforum you will find the review and pics as well.

Sent from my SM-G935F using Tapatalk

 

[Nikhil]

:withStu: to add to what kish said check what temps the car is running at. If its constantly running cold your thermostat could be shot. Which could lead to the car fueling a bit more to get to optimum temps

 

[nirvash]

would also recommend looking into a carbon clean/walnut blasting

 

[akash]

That fuel consumption is bad.

I would do what the others above have suggested.

 

[Little Goliath (Daniel)]

Definitely Carbon build up, don't fix/replace anything before you do the Walnut Blast
as others suggested check with Carbon Doctor

 

[Kubs]

HI,

If you are in the JHB area contact Yosh from Dark Artz Performance.
He now offers the Carbon Doctor service. [email protected]

Cheers

 

[individj]

who offers this in CT?

 

[Zound]

This is what the valves generally look like.

 

[Zound]

Tried a little bit of carbcleaner and then heavy duty oven cleaner with a tooth brush, with this result:

Will try to improve with a couple more repeated passes.

 

[nirvash]

who offers this in CT?

A company called C-TEQ do it, I did some work for them before,

@zound, nice! Looks like you got a lot of it cleaned. I know there is usually some loose buildup but often there is also a lot caked on that is harder to remove, good luck

 

[prmateus]

Anyone think it could be blocked up Cats?

 

[SylisM]

Sheesh that's Aventador consumption. Hope you get it sorted soon.

 

[Zound]

Anyone think it could be blocked up Cats?

I have that theory in mind too. If the car had a leaky fuel injector and was over fuelling for any significant amount of time then the cats could have been damaged by the extra fuel igniting in the exhaust system.

---

However I'm not quite sure how to check the condition of the cats with a relatively easy test.

Anyway, I've finished the valve cleaning and installed a new battery. So all adaptations are reset.

I took the car for a test drive and the fuel consumption has come down a small amount, but I don't think that I've found the crux of the issue.

Coolant temperatures are to be investigated next. I've got a feeling this beast is running cold and not allowing the motor to get to efficient operating temperatures. Will find out tonight

 

[M3_devil]

Normal temps is between 110 and just under 120.

 

[Zound]

So temps are definitely not where they should be.

Using the cluster to unlock the engine temps I went for a 30-minute drive of varied driving, including traffic and highway runs.

The cluster indicated temperatures between 86 and 94 degrees celsius. Nothing higher than that.

That run that I did I was able to average 16 litres per 100 km's , which is definitely an improvement but I still think the cooling issue is affecting the car.

So, thermostat?

 

[Kish2604]

Normal temps is between 110 and just under 120.

This is oil Temps quoted by M3_devil and not water... My water temps are almost consistent at between 190-210 degrees Fahrenheit which is about 87-95 degrees celcius during logging and full throttle acceleration from 3rd till 6th gear.

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[M3_devil]

Omw. Thanks kish. Didnt read post properly.

 

[Marco7]

I know im very late pn this post but did you find the fault