Real world fuel economy from new GE Jazz

[rossw]

yes, it's auto/VTI-S. Did I hear it right? using paddle shifters results in lower fuel consumption? (p.terribilis) - wow 621 kms. Haven't even gotten to 400kms on a full tank.

Can someone post their intake/exhaust that gained them 1/1.5km i.e. twinloop? Is that both for 1.3/1.5L M/Auto versions?

E10 gives better fuel consumption/regular unleaded? Is that Caltex/Shell/whichever?

E10 will theoretically give you worse fuel consumption by 3% due to the lower calorific value. That balances against the slightly higher octane (about 93 instead of 91 if the ethanol is blended with regular unleaded) that allows more ignition advance. I haven't found much noticeable difference between regular ULP and E10, but I can't get regular ULP here anymore, it's E10 or 95 octane now. I use E10 and it works fine.

[debowen]

Don't buy the 1.3lt engine Jazz. My mate bought one for his wife after driving a 1.5lt for the last two years. The 1.3 does no better in city fuel consumption and wouldn't pull your hat off. He had two large mates in the car recently and it struggled to get up the steep ramp in a car park. As I wrote before I get 6.75lt/km from my 1.5 vts and that gave me over 630km to the tank. By the way, the tank (which is under the front seats) and the long filler pipe hold about 43 litres filled to the neck of the screw cap. Don't fill this much unless your driving about 20 km straight off or parking in the shade. The expansion of the fuel when it warms up will stress the plastic, especially the joins at the tank and the filler!

[rubyjazz]

E10 will theoretically give you worse fuel consumption by 3% due to the lower calorific value. That balances against the slightly higher octane (about 93 instead of 91 if the ethanol is blended with regular unleaded) that allows more ignition advance. I haven't found much noticeable difference between regular ULP and E10, but I can't get regular ULP here anymore, it's E10 or 95 octane now. I use E10 and it works fine.

That's what I thought E10 should be worse. Is cruising on neutral bad? I sometimes do this when not in cruise control and see the consumption drop bit by bit.

[rossw]

That's what I thought E10 should be worse. Is cruising on neutral bad? I sometimes do this when not in cruise control and see the consumption drop bit by bit.

If you coast in neutral, the engine will idle and use fuel. If you coast down a hill in gear, the fuel will shut off completely. you can verify this from your instantaneus fuel consumption, which should drop to zero when you are coasting.

[rubyjazz]

If you coast in neutral, the engine will idle and use fuel. If you coast down a hill in gear, the fuel will shut off completely. you can verify this from your instantaneus fuel consumption, which should drop to zero when you are coasting.

confusing. the instantaneous fuel consumption i think drops to zero in neutral.
how can fuel consumption shut off when the engine is revving higher in gear than in neutral/idle?

[rossw]

confusing. the instantaneous fuel consumption i think drops to zero in neutral.
how can fuel consumption shut off when the engine is revving higher in gear than in neutral/idle?

Fuel consumption shuts off when you are coasting because the injectors simply don't open. In a modern engine, the fuel injection rate is decided by the computer, rather than approximated using the airflow like it is in a car with a carburetor.

Each injector has a little solenoid in it that pulses rapidly. Each pulse allows a measured amount of fuel in. The longer the pulse, the more fuel.

When you have your foot off the accelerator, and the RPM is above a set value, the computer knows you are coasting and simply doesn't open the injectors. The engine is kept turning by the wheels. As soon as you add throttle, the computer starts opening the injectors again.

This doesn't happen in neutral, because in neutral with no throttle, the engine is idling. In order to keep the idle going the computer must add some fuel (although not a lot). The consumption gauge shows zero when you stop in neutral because you aren't moving. That's the way Honda have chosen to deal with the divide by zero problem. (x litres/0 km)

[rubyjazz]

^^thanks for the clarification, I was also thinking about cruise control in downhill. I think that definitely do not turn off the injectors (am I right?). That should consume more fuel than idle. Or is it the same with coasting in drive foot off accelerator?

[rossw]

^^thanks for the clarification, I was also thinking about cruise control in downhill. I think that definitely do not turn off the injectors (am I right?). That should consume more fuel than idle. Or is it the same with coasting in drive foot off accelerator?

I guess it depends on the hill. If it is steep enough that you can coast down it in gear with the throttle closed, then the cruise control will do that too. You might even pick up speed unless you change down or use the brakes, either of which will cancel the cruise control anyway.

[Everybody2]

Hey all,

I haven't posted in quite a while...not really since buying my Jazz.

I'd like to start by saying this - what a solid little well made decent performer and versatile vehicle this has turned out to be - definately no regrets!

I love checkin' out the fuel consumption of my little Jazz, and it's interesting to see that some people up here are experiencing the same effects that I am too.

So the official fuel consumption figure is 6.1 for the Jazz VTI-S built in 2007.
I fill up and reset the counter, it starts high for the avg however that's because most of the work you do to get out of the gas station is stop/start.

Typically around the city I get an average of 6.9L/100k's, the worst I ever got was 9.3L/100k's (the wife was driving - she has a lead foot), and the best I ever got was 5.2L/100k's using only the CVT mode (no paddle shifters) and only city work.

I was only able to achieve the 5.2L/100k's by making sure I estimated lights and coasted as much as I could without interrupting traffic. Acceleration was limited to 2500rpm which is fine for city driving anyway, speeds we up to 80 on short freeways.

I find the economy is best at around 50kph, the Jazz uses 3.2L-3.4L/100k's on flat tarmac of good quality in CVT mode, and revs a little over 1100rpm tyres are inflated to 3psi higher than recommended cold spec.

When the speeds get up, the fuel consumption starts to get high too.
At 100kph, the consumption is about 5.4L/100k's flat tarmac with little/no wind. The same speed using the paddle shifters in 7th gear after it selects it's highest ratio (after about 15 seconds of selecting 7th) and the fuel consumption drops to about 4.8L/100k's.

so what i've managed to work out is if you drive below 70kph, the CVT does best, however if you're doing speeds above 80kph, it tends to be better using the paddle shifters and selecting the highest available gear for cruising (7th speed from 51kph upwards).

the very best i've been able to do out of short trips (ie. not a full tank) is 4.8L/100k's, this was mainly around town (note: not city - town), mostly 60kph or below, and your typical traffic lights/stop signs/giveways/etc. Not pushing up hills too much, and coasting as much as possible to stops/traffic lights/etc.

Ended up doing 80k's like this, but then had to hand the keys over to my tiny-but-mighty wife. I think the tank finished up on about 6.2 or something....still good none-the-less.

Generally if i'm driving, it's not hard to get above 600k's per tank (usually up to 650k's) doing mixed driving, however when my wife drives it's hard to get more than 500k's out of the tank.

[dyljoy]

I think I should change my driving habbit from now, coz my GE8 Jazz with auto transmission never can achieve over 450km when fuel light on,. Maybe coz my left foot and always aircon on.

[rossw]

I think I should change my driving habbit from now, coz my GE8 Jazz with auto transmission never can achieve over 450km when fuel light on,. Maybe coz my left foot and always aircon on.

Plus yours is the later model 5 speed auto not the CVT. Why Oh why did they drop the CVT?

My GE8 is a manual ('cause I couldn't have a CVT) and I get similar numbers as Everybody2. Just remember the dash gauge is about 10% optimistic.

[Everybody2]

I probably should've noted, when I bought the car I confirmed it's speedo against 2 GPS units (one navman one tomtom), as well as confirmed the fuel consumption avg figure against the amount of fuel I had acctually used in the tank at each fill.

I monitored the fuel consumption over about 5 tanks when I first had the Jazz....it was accurate enough to be indistinguishable.

I should've also pointed out, the highest fuel consumption was also in summer and the air-con on basically full-time.