Meriva 1.4 poor fuel economy

Ultrasonic

forgotmyname wrote: »

More revs does not mean worse fuel consumption.

Best economy = where the cars greatest torque figure is. Unless you dont require all that torque to keep moving.

With respect I'm going to have to completely disagree with that.

Best engine efficiency (max. BSFC) typically occurs at high load at revs corresponding to the peak torque, but this does not mean that optimal fuel economy (mpg) is achieved at this same rev value. Your caveat about not requiring max. torque applies virtually all of the time.

You have to try very hard to find any car where optimal fuel economy isn't achieved at the lowest speed that the engine is happy in top gear, and the faster you go from then on, the lower the fuel economy is. See for example the graph on page 11 of this useful VW booklet:

http://en.volkswagen.com/content/medialib/vwd4/vw_international/4_company/4_3_overview_sustainability/Nachhaltigkeit/Produkte/Recycling/effizient_unterwegs-pdf/_jcr_content/renditions/rendition.file/effizient_unterwegs.pdf.

You can have a debate at low speeds and when accelerating, but for steady-state driving above about 30 mph higher revs virtually always does mean lower fuel economy.

forgotmyname

I doubt their figures work on the road. 6th gear at 40mph. That may apply to a car on the rollers in a test lab.

But on the road where your flat road maybe up and down even slightly.

I tested my car with an ODB gauge giving accurate data. Without going into the exact fuel flow data. The throttle usage in 5th gear at 40mph was higher than when staying in 4th gear.

4th gear 9% throttle usage, 5th gear 18% throttle usage at the same speed (40mph) There was also an increase in the amount of fuel being injected when in 5th gear.

Obviously that varies between cars and the gear ratio's. Whats the top speed on their test car.

The linear lines on their chart seems a bit made up to me. I doubt you will see that on the road in daily use.

As the power and torque dip and peak at different revs the engine will be in its powerband.

There chart doesnt show this.

Seen the power and torque curves from cars on the rolling road. Unless its a highly tuned car they are not linear improvements.

I am glad you disagree, But i am only going on the tests i did and i usually say it will vary a lot on the cars powerband and gearing when i mention it.

I take manufacturers tests with a pinch of salt. Manipulating the figures is something they have done for many years.

Ultrasonic

Forgotmyname - thanks for taking the time to reply. Here probably isn't the best place for this discussion but I'll try to reply to your points.

forgotmyname wrote: »

I doubt their figures work on the road. 6th gear at 40mph. That may apply to a car on the rollers in a test lab.

But on the road where your flat road maybe up and down even slightly.

On a flat road my car (with a VW 1.9TDI PD engine) will do 30 mph in 5th, so 40 mph in 6th doesn’t sound ridiculous to me.

I know of one test that I believe wasn’t on a rolling road that shows similar results, from a What Car article in 2008. The graph is tiny but you can see the results in the following link:

http://www.whatcar.com/car-news/fuel-economy-making-every-gallon-count/the-test-findings/233124

I have the paper copy and so can explain that the horizontal scale shows speed from 30 mph to 100 mph, and the vertical scale plots fuel economy 0 to 90 mpg. The results are for five different cars all driven in top gear (three were 6 speed and two were 5 speed). The test details are poorly described here, but I believe the reference to satnav timing gears means it must have involved moving cars rather than a rolling road.

I tested my car with an ODB gauge giving accurate data. Without going into the exact fuel flow data. The throttle usage in 5th gear at 40mph was higher than when staying in 4th gear.

4th gear 9% throttle usage, 5th gear 18% throttle usage at the same speed (40mph) There was also an increase in the amount of fuel being injected when in 5th gear.

While I appreciate data, I’m not convinced that throttle position data alone tells us anything useful. Throttle position will relate to the amount of fuel injected per injection, and there will be fewer such injections per unit time in a higher gear due to the lower engine revs. At the very least you’d need to weight the results for the difference in revs, and I have a suspicion that it may be more complicated than that (e.g. does the fuel injected vary linearly with throttle percentage?)

What we really need is an indicated fuel consumption (L/min) or fuel economy (mpg). Please do go into the fuel flow data if you have it, because that would be informative.

I have a ScangaugeII sitting around somewhere for what it's worth. It's not attached to my car as it basically told me what my trip computer already did, which is that for me fuel economy in top gear behave as indicated by the VW graph.

Obviously that varies between cars and the gear ratio's. Whats the top speed on their test car.

Not sure why you ask about the top speed, but the booklet says the data is for a 90 kW (122hp) 1.4 TSI Golf, which going by the VW website has a top speed of 126 mph (203 kmh).

The linear lines on their chart seems a bit made up to me. I doubt you will see that on the road in daily use.

Yes it’s going to be harder to get such neat data on a road, but that’s a reason for using a rolling road (which like you I assume they used).

As the power and torque dip and peak at different revs the engine will be in its powerband.

There chart doesnt show this.

Seen the power and torque curves from cars on the rolling road. Unless its a highly tuned car they are not linear improvements.

This you know far more about than me, and I don’t pretend otherwise. But from a fuel economy point of view I’d have thought a BSFC plot would contain all of the relevant info, and looking at these supports the basic idea of low revs in top gear being optimal (e.g. this).

I take manufacturers tests with a pinch of salt. Manipulating the figures is something they have done for many years.

Oh absolutely. But you appear to be suggesting that the basic advice to change up as early as possible to obtain maximum fuel economy is wrong, and that’s quite a bold claim. It would be in VW’s best interests to promote the most efficient way to drive their vehicles, in order to reduce complaints from customers about poor fuel economy. So I don’t really see why they would want to mislead people about that?

forgotmyname

We could do this until the landlord calls last orders and throws us out. Or gets up the next morning and says aint you gone home yet.

My cars the same, It will happily pull 6th gear from below 50mph. But it actually uses more fuel.

My test was not just the throttle position but also measuring the fuel flow at the same time. Posting all that data along with boost and engine temperatures would be pointless. As every car would vary to some degree, Even 2 identical cars.

I honestly thought that my calculations were wrong also. 1st time i noticed it was doing 50mph in 6th gear. Used more fuel than 5th gear.
I thought it was down to a not very accurate mpg reading on the computer.
But the OBD tools backed that up.

I then repeated it on the same stretch of road at 40mph in 4th and 5th. Same results.

I also came from the era of change up to the highest gear ASAP for better economy.

But this seems not to be the case. A few guys with the 1L turbo focus also found that using more revs didnt use more fuel.

Cars gearing and top speed play a big part in what makes a difference.

1500kg 2L 130bhp 4x4 tows better than a 1500kg 2L 130bhp saloon.
Why? Because the 4x4 will be geared for a top speed of 100mph ish. Where the saloon will be geared for 130+mph.
Gearing on the 4x4 will be lower so better pulling power from 1st gear and the other gears dont need such a wide spread.

Seriously try it. Im not saying it will work for everyone or all cars but you have nothing to lose.

Enjoy.


PS.. Have we bored everyone to death yet?

Weird_Nev

To be honest I'm amazed you're getting that good a return out of it.
The 1.4 is a small engine, the Meriva is not a particularly small vehicle.

Check it's been serviced, check the tyre pressures and if you're feeling flush check the alignment (if there's any hint of uneven tyre wear then do it anyway).
After that, you're stuck with the basic physics of the engine and mass it's hauling around. I'd be pleased with anything over 30mpg from that car.

We used one at work around London, it was stuck in the low 20's.

thebullsback wrote: »

Meriva ...worst vehicle I ever had Dull/thirsty and a serious accident waiting to happen thanks to ...electric power steering .
Take my tip nd get rid .....please

I do agree, sadly. One of ours "fell over" during hard cornering. I find them pretty hateful vehicles, but then many people find them well suited to their needs, so who am I to disagree?

bigjl

I have one of those little OBD's and Dash Command.

I have found getting up to speed fairly fast and then adopting a kind of press and glide use of the throttle allows the ecu to cut off fuel completely on most moderns vehicles.

Which was confirmed with the fuel flow part of Dash Command.

This may be more specific to diesel I don't know.

A lot of fuel is used getting up to speed so I tend to do as I have suggested.

I have tried to do the eggshell throttle technique and noticed on my regular routes that it meant I was always on the throttle, very little periods of coasting.

I think hypermiling techniques also use this idea, I seem to remember a person in the US described it as "Pulse and Glide".

I have made it a bit of a challenge to get the fuel flows to show nothing as often as possible.

And to get back to the OP.

A relatively old school petrol engine like that 1.4 is never going to win the economy stakes.

High 30's might be all it can give on mixed use.

Especially when you consider that the turbo diesel versions would probably give mid 40's in the same use.

The meriva is an old design and the engines are fairly old aswell.

Though that little 1.4 is likely to outlive most little diesels.

Should be a long lived lump.

And the electric power steering problems were slightly overblown.

I know a few people with them and they never had any problems.

Though as electric assisted steering can be affected by other loads on the electrics I wonder if part of the problem is similar to people thinking their hydraulic power steering is iffy when it is hard to turn with very low revs from the engine?

Until it affects the OP I suspect it is something not to worry too much about, though due to the publicity it should be an easy fix!

Ultrasonic

I'll keep this brief!

forgotmyname wrote: »

My test was not just the throttle position but also measuring the fuel flow at the same time. Posting all that data along with boost and engine temperatures would be pointless. As every car would vary to some degree, Even 2 identical cars.

True, but it is interesting if the fuel use figures do show the improved economy you implied by posting the throttle data.

I thought it was down to a not very accurate mpg reading on the computer.
But the OBD tools backed that up.

I think that is always going to be the case, since presumably the on-board computer uses exactly the same OBD data to calculate the displayed mpg.

Seriously try it. Im not saying it will work for everyone or all cars but you have nothing to lose.

I've done a comparison at 30 mph on a flat road before, where 5th beats 4th which beats 3rd etc for economy. Or at least in terms of the displayed economy it does - I've had people before suggest this may be innacurate, at which point I'm back in the dark! I haven't done a test at higher speeds, and doing so up a hill would be very hard to do repeatably, which is why I then fall back on example BSFC plots (I can't find one for my exact engine/car).

I'll shut up now.

forgotmyname

Yeah i think we maybe diverting this thread too much. Sorry to the OP. But hopefully you may get some tips to try.

The OBD figures do give more accurate data compared to the fuel computer.
Again thats going by my car. So others may vary.

The end.

ShandyAndy_2

thebullsback wrote: »

Meriva ...worst vehicle I ever had Dull/thirsty and a serious accident waiting to happen thanks to ...electric power steering .
Take my tip nd get rid .....please

I wouldn't call it dull or overly thirsty, the steering affected very few cars.....

ShandyAndy_2

Engine peak power and power spread, Torque curve, Gear ratios and aerodynamics all play a big part in the final figures though.

Sadly the Meriva fails on all of them. Its a flabby, gutless brick shaped box.

They sell those small loaves of bread and little tins of food for Meriva owners. So as not to overload them.

Dont buy bottles or jars they are too heavy and your mpgs will suffer.

More power will give you better mpg's.[/QUOTE]


Don't think theres any need for your obnoxious comments really, the Meriva was designed with families in mind.....small on the outside and big on the inside with plenty of cubby holes and storage and plenty of seat configurations designed to carry different sorts of loads and will also go as a 4 seater with more leg room for rear passengers,higher seating which is easier to get our 2 year old in her car seat without having to bend your back, it is the perfect car for our family,being fairly cheap to run....low tax and insurance...low servicing costs, and only doing 5000-6000 miles per year a Diesel would be pointless. Would rather have the Meriva over a 5 door hatchback Astra..Focus...whatever any day of the week.