Author Topic: What MPG are you getting from your Mk1 Honda Jazz ?  (Read 201550 times)

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #315 on: January 23, 2019, 05:03:11 PM »
Further to the above post, today I had a trip into Edinburgh city centre, during the morning rush hour, and in hard frost and even freezing fog at one stage. I then travelled across the city centre and out to Danderhall on the southern edge, From there I had a trip out to Dalkeith then back to Danderhall. I then had a run back, along the city bypass, then M8, M9 and M90, before returning to Kirkcaldy. Still in sub zero conditions.
Every start was with a cold engine (blue light on).
My ScanGauge E recorded an average of 49.1 mpg (not far from the actual mpg, going by experience). The average speed was 26 mph with a max of 59 mph. Maximum revs were 2917 rpm.
I use the ScanGauge because my Jazz only has a single mpg meter. The ScanGauge gives me instantaneous readings. If your Jazz can display instantaneous readings then view that while driving.

The top display is the instantaneous reading, and the lower the average for the current journey. The secret is to try and keep the top number higher than the bottom one. Things like lifting off just before you crest a hill. Or changing up just before the crest.

smilertoo

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #316 on: January 23, 2019, 11:55:21 PM »
35psi? I have all my tyres at the specified 32psi...i might try a bit higher.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #317 on: January 24, 2019, 06:53:07 AM »
I increase the pressures slightly for two reasons. Any slight reduction in pressure between checks means that the always remain above 32 psig. Cold tyre pressures are chosen on the understanding that when the tyres heat up the pressures will rise. My tyres seldom get a chance to warm up as the bulk of my trips are only about 4 miles. The engine barely warms up, never mind the tyres.
The manufacturers choose tyre pressures as a compromise between handling, fuel efficiency and comfort. I sacrifice a little comfort (and it is very little) for a little fuel efficiency.

peteo48

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #318 on: January 24, 2019, 10:14:10 AM »
That's interesting Jocko. My motoring is even more local and short distance than yours (I follow the 33psi front and 32psi rear as per the manual for the Mk3). I might be tempted to go to 35/34.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #319 on: January 31, 2019, 09:50:35 AM »
Filled up this morning, and despite the spell of cold weather we have experienced the second half of January I still managed 52.5 mpg (on-board said 53.2 and ScanGauge 50.5). According to my average speed for the month (27 mpg) that works out at 44% Town.City and 56% Interurban.
What I did notice was that Morrisons, here in Kirkcaldy, are selling 97 RON "Premium". At 121.7p against 114.7p for Regular, I don't think I will be swapping. I'd have to push that figure to 56 mpg to make it worth while, and that is a "summer" number!

springswood

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #320 on: January 31, 2019, 12:27:37 PM »
I thought the problem with increasing tyre pressures was essentially it bulges so you get increased wear on the centre of the tread and decreased tyre life. It can also mean decreased grip. I presume you don't get this, Jocko, possibly, as you say, because your tyres often don't warm up fully. I've noticed warm tyres can show 3 or 4 psi higher but the specified pressures are for cold.
"Indecision is a terrible thing"
Or is it? What do you think?

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #321 on: January 31, 2019, 01:48:32 PM »
I thought the problem with increasing tyre pressures was essentially it bulges so you get increased wear on the centre of the tread and decreased tyre life. It can also mean decreased grip.
All the stuff I have read, and there is tons of it on Hypermiling web sites, doesn't point to this. There are many people running their vehicles with the tyres at the maximum recommended pressures as indicated on the tyre sidewall. I would never dream of doing that. To me, that is unsafe, and I have argued using the same reasons you have, but I run 3 psig over the recommended figure (5 for the rears). During the time I have been doing this I have noticed no uneven wear pattern (15,000 miles), and I am certainly not aware of any issues with grip.
The Haynes manual for the car, states that the tyre pressures are for the OEM tyres and "the recommended tyre pressures may vary if any other make or type of tyre is fitted". Add to that the accuracy of the gauge you use to check your tyres and then, who knows what pressure you are actually setting?
I haven't noticed any appreciable improvement in mpg with my elevated pressures. It just stops them dropping below the recommended pressures between checks.

springswood

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #322 on: February 01, 2019, 11:48:04 AM »
Thanks Jocko, it's what I thought but wanted to be sure. I did the same with my old tyres which lost about 6psi a week. Just had them all replaced and they cleaned the corrosion off the alloys, now holding pressure and more comfortable even at higher pressures. So I'll keep them on the high side.
Also my pump and pen type pressure gauge don't agree. 
"Indecision is a terrible thing"
Or is it? What do you think?

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #323 on: February 22, 2019, 07:21:26 AM »
Disappointing fuel consumption at the moment. Today's top up was only 50.8 mpg over 396 miles. Considering how mild the weather is I would have expected better.

Actual: 50.8       Dashboard: 53.1    ScanGauge E: 51.0

springswood

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #324 on: February 22, 2019, 08:57:43 AM »
I always suspected the 1.2 of being a good engine. I wish I could get something like from my 1.4. Still nudging the 40 mpg mark. Much of that will be down to short journeys though a 150 mile round trip to the coast only got the dash display up to 47.

Returning to the old hypermiler's trick of accelerating open throttle to reduce pumping losses I think it may be just that, an old trick. I'm now getting real time mpg display from an OBDII reader. The further I push the pedal the worse the mpg. I suppose because the pedal is no longer a throttle control it's a pot (potentiometer) that generates an electrical signal demanding power from the ECU. It's striking how the slightest movement in the pedal makes the figure plummet. But then it also shows coasting gives better mpg than engine braking. So either something in my engine stops the fuel cutting off altogether or the way it calculates mpg is misleading. Time will tell - hopefully.
"Indecision is a terrible thing"
Or is it? What do you think?

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #325 on: February 22, 2019, 10:02:28 AM »
I very, very seldom open my throttle fully. Once it goes out of closed loop it guzzles fuel. The Deceleration Fuel Cut Off only works above certain rpm. On a slower descent it is better to select 4th, or sometimes even 3rd, to get DFCO to cut in. Above 40 mph then 5th does the trick.

springswood

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #326 on: February 22, 2019, 07:29:27 PM »
That's what I thought. The suggestion from the mpg figure is that for some reason my fuel is never cutting off. I'll see if I can get the OBD reader to tell me directly.
"Indecision is a terrible thing"
Or is it? What do you think?

peteo48

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #327 on: February 22, 2019, 08:34:41 PM »
Disappointing fuel consumption at the moment. Today's top up was only 50.8 mpg over 396 miles. Considering how mild the weather is I would have expected better.

Actual: 50.8       Dashboard: 53.1    ScanGauge E: 51.0

I'd be punching the air and handing out cigars with those figures!

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #328 on: February 22, 2019, 09:53:33 PM »
I'd be punching the air and handing out cigars with those figures!
There was a time I would have been too. I remember being jubilant when my first ever tankful returned 48.3, which after 24 - 28 mpg from my Volvo was brilliant. But I have  got used to better. Today's top up knocked my overall lifetime figure (over 23.5K miles and displayed below my Avatar) from 54.2 down to 54.1. Entirely the wrong direction.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #329 on: February 23, 2019, 05:07:13 PM »
The suggestion from the mpg figure is that for some reason my fuel is never cutting off. I'll see if I can get the OBD reader to tell me directly.
To get DFCO to work, make sure you are removing your foot entirely from the throttle. If not you may be sending enough of a signal to have the ECU giving the injectors an input, and passing fuel.
Another thing to try, using the OBD, is to monitor the fuel use on a stretch of road then very slightly reduce the pressure on the throttle. You can usually add a couple of mpg to the display without affecting the speed. Sometimes more than a couple of mpg.
Another thing to do is to lift of the throttle before cresting a hill, not as, or after you crest it. Let the momentum of the car do the work.

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