E92 330i M Sport Auto MPG Issue (N52)

E92 330i M Sport Auto MPG Issue (N52)

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squareflops

Original Poster:

1,384 posts

122 months

Wednesday 16th January
quotequote all
Hello all,

I've avoided writing this post for a while as I can foresee the answers and quite rightly the answers will be "could be a lot of things". That being said I'll hold out hope that maybe someone has had a similar problem that they've fixed or at least a nudge in the right direction.

Recently purchased a 330i auto with 112k and the N52 engine. I love the car, it's superb. I am however as eluded to in the title getting 20.9mpg or there abouts regardless of how I drive it, I can re-set the trip and travel 50 miles on a motorway @ 65 and see mid 20's; maybe. Breathe on the throttle and I'm down to 20. Around town in stop start = 20mpg grumpy

The car is in very good condition and has no hesitation or other running issues, it's super smooth so no obvious plug/coil issues and no smell of petrol (it's not leaking out anywhere)

I've recently taken the car to Redish Motorsport for a PPI and all came back fine. I was hoping that a code may be stored that pointed toward say a dodgy coil etc but nothing, nothing noting anything that would cause such bad mpg. One thing they did note was that the golf tee mod had been done. I removed this and on the way home from Bristol I actually saw 31mpg on the motorway, I was elated for a few hours as I thought it had miraculously fixed itself. Then over the next couple of days I saw the figure slowly creep back down to 20 and it's stayed there.

Where do I go next? I don't want to start throwing £££ at the fuelling/ignition system replacing everything under the sun in the hope that something I change is causing the issue. As I said I know there's no magic answer but it's spoiling the enjoyment of the car as I'm fixated on (unsuccessfully) raising the mpg figure and getting dejected when it won't budge from 20.

My mates e92 m3 gets 26 hard driving and 30+ on a cruise for goodness sake.

TLDR - fuel economy is crap, no obvious issues, advice please.

Robb F

4,366 posts

110 months

Wednesday 16th January
quotequote all
Just as a sanity check here, I'm sure you've thought of it already but...

Have you measured the actual mpg you're getting with distance travelled vs fuel fill ups, or are you relying entirely on the trip computer?


aquarianone

395 posts

116 months

Wednesday 16th January
quotequote all
What sort of fuel are you using..?

For what it's worth, my Zed has the same engine...and easily gets 28+ on a regular drive and 35+ on long distance.

When I had a similar drop in economy (down to low 20's)...a couple of things helped to fix it. one was a dodgy coil pack (they all been changed around 6 months prev) and the second was changing the battery (looks like it was still on the original).

squareflops

Original Poster:

1,384 posts

122 months

Wednesday 16th January
quotequote all
It's a very good point Robb and call me crazy but I have not as yet. Having raised the issue with the boys over the last few days they've recommended the same, take the issue of the computer being wrong out of the equation, although the rate it goes through fuel it certainly feels like 20mpg.

I'll be doing this next before I start spending money but I haven't needed to use the car this week and I still have half a tank. Although I'm sure in about 80 miles I'll need to refuel. I'll mechanically calculate it then. I have a bottle of Forte injector cleaner in there at the moment (£16!) although I don't think it will do much.

squareflops

Original Poster:

1,384 posts

122 months

Wednesday 16th January
quotequote all
aquarianone said:
What sort of fuel are you using..?

For what it's worth, my Zed has the same engine...and easily gets 28+ on a regular drive and 35+ on long distance.

When I had a similar drop in economy (down to low 20's)...a couple of things helped to fix it. one was a dodgy coil pack (they all been changed around 6 months prev) and the second was changing the battery (looks like it was still on the original).
Always Super from Sainsburys/Tesco predominantly.

I'd be the happiest man on earth with those figures bud. Hm interesting about the battery, wonder if that was coincidental or contributed, strange to think that could have any effect but who knows with 'modern' cars.

You know that's my next step - coils. I can replace all 6 for lets say £200 max (ECP) and for the outlay I'm thinking it's worth the money. I've read quite a few threads that have said similar things re the coil packs. I'm more than happy to put some money into her as I really love the car. I'll take a look a the battery as I know they don't like low voltage so may replace as it's winter anyway if it's past its best.

Cheers for the info.

I really hope replacing the coils fixes it.

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PTF

3,372 posts

163 months

Wednesday 16th January
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My manual 130i will sit at around 35-38 mpg on the OBC at about 50-55 mph in 6th gear. Once up to speed i can't see an auto knocking that figure down by much (if anything).

Sounds like something's not quite right there.

Could it be a thermostat stuck open? Engine is running too cold maybe. Might be worth having a dive into the secret menus (google it) to see what the coolant temp is.

cerb4.5lee

10,879 posts

119 months

Wednesday 16th January
quotequote all
squareflops said:
My mates e92 m3 gets 26 hard driving and 30+ on a cruise for goodness sake.

I find it hard to believe that he gets 26 mpg from the E92 M3 under hard driving because the official combined figure is only around 22 mpg. I used to get low to mid 20's out of my N52 330i auto overall, but on a run if I drove like a saint I would see around 36 mpg, so something does seem wrong with yours.

aquarianone

395 posts

116 months

Wednesday 16th January
quotequote all
One other random thought...what size wheels/tyres (also check tyre pressures) have you got on?

I've recently switched back from 19's to 18's and rather randomly noticed it seems much content / less thirsty on the 18's....

(or maybe it's in my head as i'm not being tortured as much smile

Edit to add - my numbers are from using Tesco Momentum pretty consistently.

Edited by aquarianone on Wednesday 16th January 15:26

pedarby

11 posts

2 months

Wednesday 16th January
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I've read various threads regarding issues with worn/failing DISA flaps in the air intake manifold causing reduction in performance and economy - might be something worth checking?

clockworks

2,661 posts

84 months

Wednesday 16th January
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Have you checked that the OBC is set to use imperial gallons, not US gallons?

No idea if you have this option on your car, but I had it on my E61. For some reason it was set to US gallons when I bought it secondhand.

Gary Kinghorn

27 posts

22 months

Wednesday 16th January
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Make sure it's running in metric MPG rather than US Gallons. I had this on my E60.

laingy

449 posts

180 months

Wednesday 16th January
quotequote all
cerb4.5lee said:
squareflops said:
My mates e92 m3 gets 26 hard driving and 30+ on a cruise for goodness sake.

I find it hard to believe that he gets 26 mpg from the E92 M3 under hard driving because the official combined figure is only around 22 mpg. I used to get low to mid 20's out of my N52 330i auto overall, but on a run if I drove like a saint I would see around 36 mpg, so something does seem wrong with yours.
My m3 averages 19, no way do you get 26 with hard driving .

squareflops

Original Poster:

1,384 posts

122 months

Wednesday 16th January
quotequote all
Cheers for the replies all. In chronological order

Thermostat - yes has been mentioned also, I'll have a look at the hidden menus.

The m3 MPG - highly anecdotal I realise, just going off what he told me but did raise an eyebrow when he mentioned those very frugal numbers.

Running 19" style 225s with 35 all round. On an unrelated note I've had 3 punctures since owning the car, not a fan of 19's for puncture resistance! Think I'm just going through an unlucky spell hehe

DISA flaps - hmm first I've heard of them but if the coil packs don't fix it I'll look into that next cheers bud.

metric vs gallons, would be surprised if it was that but will certainly check.

again laingy - agree, I'll see him tomorrow and call chinny reckon on him redcard

I'll keep this updated and hopefully a resolution when I sort it so there's some closure

Mr Tidy

7,609 posts

66 months

Thursday 17th January
quotequote all
Well on an E92 at least you should have a temperature gauge IIRC so you should be able to get an indication if the engine is running cold due to a dodgy thermostat.

Your fuel consumption does seem excessive, but of course it does depend on how, when and where the car is used.

My manual E91 with a 2.5 litre N52 does 95% of it's miles outside of rush hours on motorways and NSL dual-carriageways and the OBC is showing 33.6 mpg (slightly better on my Excel spreadsheet).

Coincidentally my manual Z4 Coupe (3 litre N52) is also showing 33.6 mpg on the OBC - it never does Tesco shops, but does get driven a bit quicker. rolleyes



squareflops

Original Poster:

1,384 posts

122 months

Thursday 17th January
quotequote all
It did have a water pump just before I bought it, maybe the thermostat wasn't changed and could be a good shout, I'll need to find the stats for the water temp also. I'd like to take it out tonight but will have to wait until the weekend to hopefully get this tyre repaired.

I'm hovering over the buy now for 6 coil packs from ECP so will no doubt pick those up soon. Delphi or Bosch though.

And a battery is £100 after discount yikes. Will only replace that if actually necessary, will see how it looks on the weekend too.

kiethton

10,588 posts

119 months

Thursday 17th January
quotequote all
squareflops said:
It did have a water pump just before I bought it, maybe the thermostat wasn't changed and could be a good shout, I'll need to find the stats for the water temp also. I'd like to take it out tonight but will have to wait until the weekend to hopefully get this tyre repaired.

I'm hovering over the buy now for 6 coil packs from ECP so will no doubt pick those up soon. Delphi or Bosch though.

And a battery is £100 after discount yikes. Will only replace that if actually necessary, will see how it looks on the weekend too.
I'd take the free option of checking the coolant temps first - it may flag the issue sooner and avoid some unnecessary expense

DaveZed

3 posts

13 months

Thursday 17th January
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After one of the services (at the BMW agents) of my 2005 E90 330i a few years ago I noticed that the fuel consumption on the computer was suddenly horrendous. A quick check of the calibration parameter in the hidden OBC menu revealed that a technician must have fiddled (intentionally or otherwise). I reset it back to the number it should have been (I tweak it occasionally myself if it seems a bit inaccurate compared to my tank to tank calculations). The default is 1000. If it isn't close to that, try that as a start. Mine is currently around 1010 I think, so only a 1% difference from the default. If you aren't familiar with the hidden menu or aren't comfortable playing around with those settings, perhaps there is someone in the area who could assist in checking this for you?

squareflops

Original Poster:

1,384 posts

122 months

Thursday 17th January
quotequote all
Will do kiethton

Dave - a thousand what confusedlaugh jeez these new cars. This is why I like my 27 year old Rover 216 GTI! Would that simply give an incorrect trip reading or actually effect consumption? The former I'm guessing. Something else I'll check cheers for the info.

DaveZed

3 posts

13 months

Thursday 17th January
quotequote all
Correct. It's just a measurement calibration setting to correct errors in the accuracy of the fuel consumption indication on the onboard computer. No effect on the engine itself. Incidentally, it's also possible via that hidden menu to see what the actual coolant temperature is, since I assume yours also has no temperature gauge? If you Google "E90 hidden menu" you should get info on how to access it on the instrument panel (using the odo reset button), but it is a bit fiddly.

Sorry - I should have said "greetings" to you all, since I only realise now that i hadn't posted before, although I have been lurking for some time, and have received much useful info here already!

BOR

3,825 posts

194 months

Thursday 17th January
quotequote all
What changed when you removed the golf tee ? Presumably you reconnected a vacuum hose to a tapping on the exhaust?

Is this vacuum hose split or loose on at the connection? If it is leaking, is it causing a lack of vacuum signal somewhere else?

Is the throttle controlled with a stepper motor electronically or does it use a vaccuum signal ? The throttle should normally be fully open as soon as possible off idle. If it is remaining closed, then that would be a cause of increased fuel consumption ( on this engine, air consumption is controlled by the VVT system changing intake valve lift, the throttle is a safety back-up).

I can't remember if this engine has a separate vac-pump for the brake servo, but if it doesn't, and the ECU is seeing a lack of vacuum, then it will fail safe by closing the throttle blade to generate a vacuum in the inlet manifold.

I would de-tattch and then re-attach the vac hose.