I cant seem to get over 18 mpg - something wrong?
- Thread starter alexman
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thattallchap
Member
Getting an Avg of about 32mpg at the mo. Also found that I can increase it to 34mpg when using Sports mode, due to the sensitivity of the go pedal.
I wouldn't take too much notice of the computer readouts, mine generally lies around 21mpg with an average of around 29-30 mph (seeing as I do a lot of shortish city trips). The economy has been creeping up whilst running Tesco 99 (rather than Sainsburys super) - even after using nearly a full tank in an hour on track I'm reading 23.4 for February/March.
Personally I don't really care that much as work picks up the tab thanks to a generous fuel allowance but the bottom line is nothing is wrong with your car. It's fairly thirsty but not that bad - just think of those M5/M6 owners - 12ish mpg around town...
Personally I don't really care that much as work picks up the tab thanks to a generous fuel allowance but the bottom line is nothing is wrong with your car. It's fairly thirsty but not that bad - just think of those M5/M6 owners - 12ish mpg around town...
Z4coupebeaver
Member
A lot depends on the kind of journey you are doing. I can imagine lots of city driving would get you down to low 20s. My trips are all quite long with medium to high (sometimes well into 3 figure high - 69.9 if plod is reading!) so fuel economy is not an issue. Since getting my M I've worried a lot less about the price of fuel as each journey feels like it's good value for money 
Seriously though - if you are getting under 20, I would get it onto diagnostics as it sounds like you've got neat petrol coming out of your exhaust.
Seriously though - if you are getting under 20, I would get it onto diagnostics as it sounds like you've got neat petrol coming out of your exhaust.
No, no, no! If you're getting under 20 you are using the car as it should be used. No diagnostocs required. Sorry but if you aren't then the car is not being exploited to anywhere near its potential. If you are happy with that then I won't criticise but please don't tell those those of us that utilise the performance that there is a problem with their engine! Get a grip.
EdButler said:All i can say is... ouch!! The combined book figure for the M is 23.3. Mine (3.0i) is very easy to get 10-20% over that on the OBC so anyone getting below 20's there maybe an issue.
If you do think theres a problem, check to see if the sparkplugs show rich running. I'd then look at refreshing the pre-cat lambda (known issue on the M's). Make sure you use High Octane fuel, it pays for itself.
One common misconception is that light throttle is the most efficient way of driving... It isn't. Accellerate purposefully at 2/3rds throttle with 1.5-2.5k rpm as it reduces pumping losses.
I agree with Ed. I normally get about 25mpg in my 3.0si, mostly doing 99% city drive/stop start short journies. On my day off I went for a bit of spiritted run on A/B roads with no stops/traffic but revving the car to 4-6k constantly - surprisingly it gave me an average of 25mpg as well!
So I think our Zeds dont like traffic lights
Shipkiller
Lifer
All BMW engines drink fuel when you use the throttle a lot... I don't me a heavy throttle, I mean a lot of little to medium throttle changes.
One of the reasons this cars accelerate so well compared to other cars in the same power range is BMW dumps more fuel into the engine for acceleration. IE opens the fuel injector dwell time. There are other things too that happen.
That being said, everyone here is correct, don't gauge your fuel economy based on that dreadful thing. Use the manual method.
After doing that and if you still think your mileage is low, then there really is one probable cause. You have weak O2 sensors. This is a known problem with the S-54 engine.
I had the same issue with the Roadster and tracked it back to this. There is an old thread on here from me about this. http://www.z4-forum.com/forum/viewtopic.php?f=3&t=4488&start=0
Since you are not throwing any codes, the only way to tell is to hook the car up to a machine, either at the dealer or someone who had an ODB-II reader on a laptop, to monitor the operation of the O2 sensors. I have one of those and thats how I figured it out.
O2 Sensors operate at a voltage level of .2 to .9 volts. If the sensor is consistently reading low, like in the 0 or .1 to .4 or .5 range, then they are telling the DME that the engine is running lean and the DME compensates by adding more fuel.
I really think if you had a bad DME you would have all sorts of problems and codes.... O2 sensors are the most probable.
One of the reasons this cars accelerate so well compared to other cars in the same power range is BMW dumps more fuel into the engine for acceleration. IE opens the fuel injector dwell time. There are other things too that happen.
That being said, everyone here is correct, don't gauge your fuel economy based on that dreadful thing. Use the manual method.
After doing that and if you still think your mileage is low, then there really is one probable cause. You have weak O2 sensors. This is a known problem with the S-54 engine.
I had the same issue with the Roadster and tracked it back to this. There is an old thread on here from me about this. http://www.z4-forum.com/forum/viewtopic.php?f=3&t=4488&start=0
Since you are not throwing any codes, the only way to tell is to hook the car up to a machine, either at the dealer or someone who had an ODB-II reader on a laptop, to monitor the operation of the O2 sensors. I have one of those and thats how I figured it out.
O2 Sensors operate at a voltage level of .2 to .9 volts. If the sensor is consistently reading low, like in the 0 or .1 to .4 or .5 range, then they are telling the DME that the engine is running lean and the DME compensates by adding more fuel.
I really think if you had a bad DME you would have all sorts of problems and codes.... O2 sensors are the most probable.
"No, no, no! If you're getting under 20 you are using the car as it should be used. No diagnostocs required. Sorry but if you aren't then the car is not being exploited to anywhere near its potential. If you are happy with that then I won't criticise but please don't tell those those of us that utilise the performance that there is a problem with their engine! Get a grip."
You're missing the point of the OP. He said that his mpg had dropped from his norm. If he hasn't changed his driving style then something else has changed. On your general point I can get 8mpg out of a track day but normal fast road driving in sport mode I get 26 ish mpg. Of course if I was to drive like a cnt and rev the nuts of the thing before I changed gear then I could probably run a consistent mpg of less than 20.
Get a grip 
You're missing the point of the OP. He said that his mpg had dropped from his norm. If he hasn't changed his driving style then something else has changed. On your general point I can get 8mpg out of a track day but normal fast road driving in sport mode I get 26 ish mpg. Of course if I was to drive like a cnt and rev the nuts of the thing before I changed gear then I could probably run a consistent mpg of less than 20.
Get a grip bruss said:"No, no, no! If you're getting under 20 you are using the car as it should be used. No diagnostocs required. Sorry but if you aren't then the car is not being exploited to anywhere near its potential. If you are happy with that then I won't criticise but please don't tell those those of us that utilise the performance that there is a problem with their engine! Get a grip."
You're missing the point of the OP. He said that his mpg had dropped from his norm. If he hasn't changed his driving style then something else has changed. On your general point I can get 8mpg out of a track day but normal fast road driving in sport mode I get 26 ish mpg. Of course if I was to drive like a cnt and rev the nuts of the thing before I changed gear then I could probably run a consistent mpg of less than 20.
+1 the op has a problem. I'm getting more than the OPs mpg with nearly all stop start town driving at the moment.
Wow, I'm afraid that's simply not true.Z4coupebeaver said:
The OP says 25mpg on the motorway, so I think 18mpg elsewhere just implies the car is being revved.
Once my car is back, I'm going to suggest a test - something like.. using your Cruise Control (if you have it), hold the car at 6,000 rpm in 3rd.. reset the OBC and holding it at those revs, see what the computer tells you it's doing.
I know it's not the most reliable / scientific test, but it should prove consistent across most cars.
alexman said:
Based on this journey I would be getting around 25 I would say.
In town computer is saying 20. But in real terms its a bit less.
Either way if the OP is saying hes down at 18 on a 200 mile round trip he has a problem and you can't argue with that.
ETA - Andy he claims no hectic driving which suggests not much revs.
bruss said:"No, no, no! If you're getting under 20 you are using the car as it should be used. No diagnostocs required. Sorry but if you aren't then the car is not being exploited to anywhere near its potential. If you are happy with that then I won't criticise but please don't tell those those of us that utilise the performance that there is a problem with their engine! Get a grip."
You're missing the point of the OP. He said that his mpg had dropped from his norm. If he hasn't changed his driving style then something else has changed. On your general point I can get 8mpg out of a track day but normal fast road driving in sport mode I get 26 ish mpg. Of course if I was to drive like a cnt and rev the nuts of the thing before I changed gear then I could probably run a consistent mpg of less than 20.
I wasn't addressing the point of the OP, rather some of the general comments made about the expected consumption on these cars. I'm impressed that you keep all your really enthusiastic driving for the track, you are veritably a saint and I can't hope to live with these standards. You are also wrong to assume that I and other posters drive like cnts to have lower consumption figures than yourself, we're just enjoying the cars more than you in day to day driving.
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