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35IS MPG Figures?

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
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R.E92
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35IS MPG Figures?

Post by R.E92 » Fri Jan 13, 2017 3:22 pm

Z4M-2006 wrote:15mpg isn't normal at all..

My daily commute is nearly 7 miles of stop start traffic, from cold and mainly going uphill and my 35is easily managed early 20's in that condition... on the home run with it being downhill and traffic flowing better than usually averaged out at 24ish..

15mpg is horrendous, my 470 bhp supercharged Jag was better than that on the daily commute
Exactly.

I remember reading a thread on PH about the lowest mpg people had achieved. Even people with a V10 BMW M5 were getting 19mpg.

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35IS MPG Figures?

Post by willgill » Fri Jan 13, 2017 3:27 pm

My daily 'drive' is from my bedroom, across the hallway and into my office, so when I drive my car, I drive it :lol:

Mine came back from a full service three weeks ago carried out by Ocean BMW in falmouth, they found no issues and my MPG hasn't improved or declined before or since, maybe some cars just run lean and others rich?
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35IS MPG Figures?

Post by R.E92 » Fri Jan 13, 2017 4:09 pm

You would have to be running extremely rich to get the MPG down that far. When my injectors started playing up my MPG dropped to 24~, then one day I noticed fuel running out of my exhaust so got them replaced.

The fuel ratio on these cars is very tightly controlled. The car measures free oxygen in the exhaust gasses using two O2 sensors, one in each pipe, it then calculates the Air Fuel Ratio(AFR) from that and tweaks the fuel trims for each bank dynamically to bring the AFR closer to what the DME is requesting, which is from 14.67 during light cruising to 10.87 during high engine load and high revs.

When cars get serviced they don't check everything, they just plug the diagnostic head into the car and read out error codes. Leaking injectors and air leaks in the exhaust don't bring up any faults so it's entirely possible that there is an issue.

Leaking injectors have a whole raft of symptoms, people usually notice a couple before they go pop. You can get a rich fuel smell from the exhaust, lumpy idle, poor mpg and fuel residue on spark plugs. If you have diagnostic software you can read the AFR in each bank during deceleration and see if fuel is leaking into the cylinder when the injectors should be closed.

An air leak in the exhaust is also difficult to spot. You can sometimes hear it if you get under the car while it's running but the only way to know for sure is to get the car on a ramp and take a look with a smoke tester. If fresh air is seeping into the exhaust before the O2 sensors the car will think that the exhaust gas coming from the engine has free oxygen therefore must be running lean, and will inject more fuel to compensate, which in turn will still show free oxygen as it leaking in through the exhaust so it gets stuck in a loop of adding more fuel.

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35IS MPG Figures?

Post by willgill » Fri Jan 13, 2017 4:21 pm

I'll pop up my logs from carly and MHD when I get a chance, because I wouldn't know what a correct or incorrect AFR reading looked like! :D

I still think it's standard fuel economy, the other cars I drive return equally rubbish economy, I always put it down to my Ricky Bobby syndrome - "I wanna go fast" :driving:
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35IS MPG Figures?

Post by R.E92 » Fri Jan 13, 2017 4:29 pm

If you have MHD then that's perfect.

The MHD standard maps run slightly leaner than stock so the map won't be the cause of the problems. I think they target 11~ at full load which is about right for standard fuel.

If you have any logs then send them to me and I'll see if you have fuel issues. The best kind of log for diagnosing injector issues is a 5-10min drive with a warmed up engine and plenty of downhill coasting.
A standard WOT log in 3rd gear moving to 4th is also useful because you can see how well the fuel pump is coping and see if the fuel trims are behaving.

You need to have the following channels selected;
Fuel rail pressure
AFR Bank 1
AFR Bank 2
LTFT 1
LTFT 2
STFT 1
STFT 2
Throttle position

Along with the standard Boost req, Boost actual, RPM and "Ignition Cyl 1 crk*" along with Cyl 2/3/4/5/6 correction channels.

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35IS MPG Figures?

Post by willgill » Fri Jan 13, 2017 4:48 pm

That's very kind of you, I'm heading up to london for work tomorrow so will grab some logs en route, will give me something to do when I arrive :)
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35IS MPG Figures?

Post by sunnydays » Sat Jan 14, 2017 11:37 pm

Sgreen wrote:My daily commute is town driving, clear run in a morning at 6.30am but stop start on the way home at night and average 25 mpg. On motorway runs can average 30 - 34mpg, so 15 does seem a tad low. Are you using your onboard computer to take your mpg or manually calculating it?
Using the trip computer figures. Did a motorway commute / mixed driving today route today and averaged 30mpg.

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35IS MPG Figures?

Post by V8 Animal » Sun Jan 15, 2017 8:55 am

Smartbear wrote:
V8 Animal wrote:Why V power?
I have 3.0 TT using standard petrol mixed driving 24mpg
Hi, many people use V-power because of its cleaning capabilities, the detergents used clean the internals of your engine. Turbo engines especially can make more power using super unleaded also :thumbsup:
Rob
Yep I heard all this but I don't believe it.
I have a SL which says to use 97 Ron I doubt the beemer does.
Anyway I've tried a few tanks with it and not noticed any drops or gains.
On a dyno you may see improvements.
If you don't do short journeys a lot I doubt it will clog up.
I'm not paying 10p extra per litre for nothing it's expensive enough.
Oh and the SL is a 5.5 Bi turbo kicking out 570 bhp and normal driving I get 20mpg.
It's your money :thumbsup:

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35IS MPG Figures?

Post by willgill » Sun Jan 15, 2017 4:52 pm

Whilst I said mpg doesnt matter, I definitely get more miles from a tank of v-power/SUL, stands to reason that the increased octane and active ECU will allow the computer to run the engine leaner so the increase in filling up cost levels out over time. I see the same in the rs6 that will give an extra 30 odd miles from a tank with identical driving styles and thats just shy of 600hp
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35IS MPG Figures?

Post by Smartbear » Sun Jan 15, 2017 6:19 pm

willgill wrote:Whilst I said mpg doesnt matter, I definitely get more miles from a tank of v-power/SUL, stands to reason that the increased octane and active ECU will allow the computer to run the engine leaner so the increase in filling up cost levels out over time. I see the same in the rs6 that will give an extra 30 odd miles from a tank with identical driving styles and thats just shy of 600hp
I don't think the ecu runs the engine any leaner, what it does is to increase the ignition advance if the knock sensor allows :thumbsup:
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e89 Sdrive 20i, plenty of mumbo & good economy-the thinking bears z4
e89 Sdrive 30i, this ones busted, pass me another...
e85 3.0si sold

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35IS MPG Figures?

Post by willgill » Sun Jan 15, 2017 6:23 pm

that might be what I meant, I always thought TDC advance and fuel mixtures went hand in hand, but I learnt everything I know in the pub so it doesn't stand up to much :p
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35IS MPG Figures?

Post by R.E92 » Sun Jan 15, 2017 7:10 pm

I honestly don't think it does either of those things. It certainly doesn't run leaner that's for sure.

If you fuel is poor quality, like the 87 and 89 octane fuel they get in the US then the car will reduce ignition timing if it senses knock. I think it will also reduce the maximum boost pressure the car will target by reducing the load target. In the UK our standard fuel is pretty good, minimum of 91 octane I think.

I only ever use Tesco Momentum and Shell VPower. Tesco Momentum seems to be capable of highest power output and is also a huge amount cheaper than VPower. I only use those fuels because I have tuned the ignition timing to be at the knock threshold for 93 octane fuel, any less and it will reduce my ignition timing.

As far as cleaning additives I can't comment. I've read on several different occasions that direct injection systems don't benefit from this cleaning. I certainly wouldn't pay 10p extra per litre purely for the advertised cleaning benefits. In my opinion you are wasting money using premium fuel on a car that runs a standard engine tune.

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35IS MPG Figures?

Post by Busterboo » Tue Jan 17, 2017 10:21 am

willgill wrote:never seen 30mpg unless im going downhill with the engine off :p mine is currently on 17.7mpg average. Driving like a saint i think I got nearly 430miles from a tank which equates to about 26-27mpg.

I didn't buy the car for it's fuel efficiency :p
You were driving much better than you thought. :)

430 miles from brimmed to empty would be 35mpg and from brimmed to first warning would be 38mpg.
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35IS MPG Figures?

Post by Busterboo » Tue Jan 17, 2017 10:34 am

I'm embarrassed to say that I'm struggling to get below 29mpg. :oops:

Must try much harder. :)
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