Fuel consumption in a Brabus (Sorry for the lame question, but it's killing me!)

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Permalink Reply by Ian Pellant on August 26, 2009 at 6:36pm

Aha... a real BRABUS with turbo (not one of the decorative posers.)

I have the Australian pulse with turbo (84 bhp). None of the US smarts have the factory turbo and the BRABUS Xclusive is but a pipe dream for USA and Australia. This web forum is primarily American, so little direct advice can be offered here.

The published factory fuel consumption of for the BRABUS Xclusive is 6.7 lhk and that should be what to expect in normal driving conditions. My turbo is rated at 6.4 lhk and that's about normal for town driving. On trips I can get it down to 5.5 lhk. Air con always on. Once the turbo spins, revs to over 6,000 rpm in a blink.

When new, it was guzzling over 7 lhk. The smart does need a long run in period and I suspect (and was told by a friend who used to work at the smart dealership) that the smart does change it's ECU programing as mileage builds up. Mine certainly seemed to change at 2,000 km, 3,000 km, 5,000 km and 10,000 km. Getting quicker, smoother and less fuel thirsty at each mile post.

But I have discovered one peculiarity. There seems to be a relationship between battery voltage and fuel mix. It took me 11 months to find this out! The negative battery terminal was not tightened up when the car was delivered. The car from new had a very rich exhaust when first started. Fuel consumption as measured realtime on a ScanGauge has been inexplicably erratic. Cold starting became a problem. This last weekend I cleaned both battery posts and tightened them up and recharged the battery. It took over 12 AH to top it up. The cold starts have been diagnosed by the smart centre to be caused by the crankshaft positioning sensor... that controls ignition timing and thus affects fuel mix.

A replacement sensor is on order.. meanwhiles the car is behaving much better with a full battery and power supply The ignition advance is more stable. I suspect an interrelation between battery voltage and the sensor range. May sound silly... but check your battery conections... they may affect fuel consumption.

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Permalink Reply by Guy El on August 27, 2009 at 6:33am

Hi Ian,

Thanks for the reply!

I didn't realize that the forum was primarily American; I am aware that they didn't get the engine that should have come with the bodykit :(
But Australia? That's odd, especially since my smart is right-hand drive (Cyprus, ex-British colony), so they definitely make 'em.. I guess they just don't ship them for some reason (can't be for safety reasons, as it's the same chassis)..

I will check the battery terminals; it sounds like a good idea. The car did idle quite rich the first few days when I first received it too.

Regarding the change after 2000km, I definitely noticed that, and up until I read your message, I thought I was imagining things! The car's behavior changed quite dramatically.

Thanks again,

Guy

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Permalink Reply by Ian Pellant on August 27, 2009 at 7:42am

Hi Guy,
It's probably market size and expectations that decided smart Australia to only import the pulse - essentially the grey interior and fatter wheels and tyres, and then offer the turbo as an option. Auto is not standard. All the non-turbo Aussie pulses this year have mhd as standard. I'm happy with smart Australia's decisions.
The skinny tyres on the pure and passion are not a great match to our roads. And the Auto program is a dubious option. (I rarely use it) We are offered the BRABUS cosmetic parts, but not the engine... it's still open for turbo owners to find a third party remap to over 100 bhp.
The USA only gets the pure and passion. No pulse. No turbo. And then they get an Americanised Auto shift with a lever notorious for failure. I firmly believe that smart USA should have offered them the pulse with turbo option.
Still with suspect crankshaft positioning sensor, my smart has started first time the past two mornings and it definitely has lost that rich exhaust stink it had since new. It now has over 11,000 km on the clock and had it's first oil change this week. It did not use a drop of oil in those 11k km... testimony to a close tolerance engine.
Cheers, Ian
PS: swapping the pods around to get the tacho near the driver is the only mod I've done. It was worth the agony.

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Permalink Reply by Guy El on August 27, 2009 at 10:00am

Swapping the pods sounds like a great idea. I have also considered replacing the clock with a boost gauage too just for fun, since we have the digital clock in the dash anyway..

Over here, we are offered pretty much any smart possible, and I suppose they can do that as they keep practically nothing whatsoever in stock; it's all special ordered.

Is the "Auto" you describe different from the soft-touch/soft tip stuff (I forget the exact name they call it)? Or is it the programme that allows you to push the button on the shifter to make the car upshift and downshift for you by itself?

In "manual" mode, I've noticed that the smart sometimes ignores me and either upshifts (if it thinks my revs are too high) or downshifts (porbably to prevent stalling, as I'm slowing down) as it sees fit. Do the non-Auto ones do that too?

I must say, I do have the car in Auto mode 98% of the time, could that be the big factor in fuel consupmtion? I never thought much of it, as it rarely goes past 3000rpm before it upshifts anyway (you'd have to be flooring it for it to hold the gear).


Cheers,
Guy

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Permalink Reply by Guy El on August 27, 2009 at 10:40am

Ian,

I just read your post on , that answered a lot of my questions.

I know that the gearbox is a sequential 'box, and that the car performs the clutch functions, but I hadn't realised that it's ok to let it downshift for you in manual mode. That would make it so much easier to drive in manual..

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Permalink Reply by Ian Pellant on August 27, 2009 at 6:25pm

Guy,
In manual (softip) mode the smart will automatically downshift when the revs drop too low... touching the brake pedal will signal it that you are intentionally slowing down, so it will quickly decide to downshift then. The only exception is when I'm in the suburbs and know I'm going to do a 90 degree left hand turn at 10 kph then accelerate up a grade to 30 kph.. the smart will downshift semi-automatically, but it hasn't learnt that corner yet, so will not downshift two gears. A quick double tap on the left paddle just as I start to turn left and voila!
There is over-rev protection and the smart will upshift automatically in any stick mode if revs exceed about 6350.
The Auto program (softouch) adds the touch button on the side of the shift lever and it tries to fully automate the shifts. It really has a hard time with first gear and standing starts. Hold the pedal down too far and the turbo kicks in and everything sticks in first until over-rev pursuades it to upshift... a bit of a scream when it happens because you didn't really intend to be a hoon, but the smart decided to have a blast from the traffic lights. Flip the right paddle to spank it.
To see how quick and smooth the shifts can be, flip the paddles to go through 3 - 4 -5.. 5 -4 -3 when doing 60 kph. Up and down. The shifting is quick and smooth. It is the nose up, nose down body plunge under acceleration that gives the shift a bad name. Treat the gear shifts as you would in a traditional manual shift, dry plate clutched car and the whole process becomes a lot smoother.

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Permalink Reply by Guy El on August 27, 2009 at 7:06pm

Thanks for your time all the help Ian! Much appreciated.

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Permalink Reply by Timothy Cain on August 28, 2009 at 9:12am

My '09 fortwo PURE is now getting 49.6 UK MPG. That's with about 2400 kilometres on the odometer. My overall mileage for the 2 months I've had the car is over 45 UK MPG. This has been with air-conditioning on 75-90% of the time and a mix of highway and city. Different car, but just as a guide. I've explained each of my fill-ups here. (http://fuelthesmart.blogspot.com/)

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Permalink Reply by Guy El on August 28, 2009 at 12:46pm

Here's my summary, if you're interested:

A/C pretty much on all the time, usually only one person in the car (me), only I drive the car, Using Auto Mode. Average air temps are between 28 degrees (night) to 35-40 in the days. Mostly driven during the day. Mix of in-town and highway driving about 50/50.


27.53 liters (98 Oct)
319.3 km
8.6 l/100km
Notes: First fill ever, definitely Zero Boost, totally babied it, varied revs really gently, never went past 1/4 throttle.

28.89 liters (98 Octane)
312.1 km
9.3 l/100km
Notes: Breaking in the engine


30.29 liters (filled it with 100oct)
274.5 km
11 l/100km
Notes: Driving up to 4,000rpm no full throttle, but was going on boost


25.44 liters (100 oct)
222.8 km
11.4 l/100km
Notes: Driving up to 4,000rpm no full throttle, but was going on boost


31.45 liters (100 oct)
368.0 km
8.5 l/100
Notes: Mostly highway driving. I drove some 70km on about 5 liters of fuel, no A/C, keeping the revs really low as an experiment on the highway. Those are unrealistic driving conditions. This is probably the best efficiency this car will ever do.


20.38 liters (100 oct)
182.7 km
11.2 l/100
Notes: Some more "normal" driving now that it's past the babying stage


19 AUG 2009
28.89 liters (100 oct)
274.0 km
10.5 l/100
Notes: Usual, mix of highway and in-town

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Permalink Reply by Ian Pellant on August 28, 2009 at 6:39pm

Guy,
One thing that stands out is a fill of 31.45 litres. The smarts have a maximum tank capacity of 33 litres (5 of which shows up as reserve / finer scale fuel gauge readout).
You seem to have been fillig up at a variety of pumps. That is an unpreidcatble variable. I know my local service stations well and at one I know that one pump will deliver precise quantities (according to ScanGauage), whil another pump on a different aisle will deliver about 2 litres more than expected. Pump one is less sun exposed to pump two. The cross fall on the hardstand is different. Pumps are a much bigger variable than we may expect.
Always use the same pump at the same time of day - preferably early morning when the fuel is coolest and densest, when trying to get consumption figures.
How do you do know the turbo boost? Xclusive has a gauge?
I'm using the ScanGauge to monitor MAP in kpa. Anything over 100 kpa is obvious boost. Don't see it much in normal cruising.
Have to lead foot around town to get worse than 6.5 lhk. Your figures really are too high a consumption.
I'm off for an 800 km round trip with a dicky CKP sensor... my lhk figures may be a bit abnormal for this trip due to drifting ignition timing and mix... an adventure beckons.

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Permalink Reply by Guy El on August 29, 2009 at 10:38pm

Ian,

100% of all my fills were made at the same station, at the same pump (there aren't many 100octane pumps here). It's the same place that I fill my other cars.

The 31.45 was me coming back from a long trip on literally fumes. The fuel gauge in the car read 0.5 liters!! It was that I really wanted to go to that pump specifically. I left another town 70kms away and the car flashed low fuel and said 5 liters left just as I turned onto the highway.. I risked it, babied it with A/C off for most of the trip. I was really curious to see what kind of mileage it would get.

I would probably trust the pump more than the car's gauge. The car's gauge shows 8 bars when full, and stays on the first bar for at least 60kms, about 40-50kms on the second bar and then races through the last 6 bars. It is somewhat accurate at below 5 liters when it gets into the details.

By a boost gauge, I meant finding an aftermarket gauge that resembles the colors of the Brabus clock, and replacing the clock with a boost gauge, just for fun.

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Permalink Reply by Ian Pellant on August 30, 2009 at 4:38am

Hi Guy,
I did the round trip ok... just a bit of a worry getting the smart to cold start on both mornings.
Managed to attain 5.5 lhk driving south, then 6.1 lhk coming back. Really inexplicable differences in fuel consumption that I'm hoping is caused by the crankshaft positioning sensor being flaky. The ScanGauge shows varying fuel consumption (second by second) when steady cruising at 100 kph. MAP (Manifold Absolute Pressure) stays constant, but the mixture is obviously changing from around 5 lhk to almost 7 lhk at the same speed and load.
Turbo boost (MAP) seems to be greater in 5th gear than in 4th at 100 kph... maybe the turbo is producing more torque at the lower rpm in 5th. In 4th the rpm are higher and the power is more in the brake horse curve. (?)
The only way I reproduce your heavy consumption would be by sustained uphill drives... with no fuel saving by returning downhill.
I hope the replacement sensor arrives this week...
One reason for the fist bar on the fuel gauge lingering is that the gauge measures the level in the fuel tank.. it does not try to guess how much is in the filler pipe so until that is used and the tank starts to drain, the gauge stays on full.

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