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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
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Fuel consumption of M13A VVT engine regarding to revving

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03 Nov 2018 08:41 #197267 by Bosanek
I remember that a few people wrote here in the past that they experienced increased fuel consumption with M13A VVT engine when it was predominently driven "lean" (i.e. rarely revved over cca 3000 RPM). When they changed their driving style to regularly rev it to 4000 RPM and more, they allegedly recorded improved fuel consumption.

But like I said, this is from my vague memory.

Is this phenomenon true, and what is the technical logic behind it?

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03 Nov 2018 12:28 #197273 by Lambert
Last weekend I was in Scotland with friends indulging in some spirited driving and with sustained periods of 4000 rpm I was still returning 32.5 mpg over 1300 miles.

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03 Nov 2018 12:35 #197274 by Delux
Sometimes known as an 'Italian tune up' revving the engine up can help burn off carbon deposits from upper cylinders, o2 sensors etc.

Also, without going to technical over it, many of the things the ECU looks at influence the fuel injection. The ECU sometimes has to calculate some of these things based on time and readings from other sensors. When the software is designed it is designed to be the best compromise to suit all drivers therefore someone else starts driving the car differently, the ECU may not be using the most efficient fuel map. It will change its self over a given time but taking the car out and giving it a good kick in should speed this up.

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04 Nov 2018 12:55 #197296 by Busta
Keeping the engine speed below 3000rpm will mean that in order to accelerate at a reasonable rate you are using full throttle a lot of the time, which certainly isn't the most economical way to drive.

But having recently done the sums on money saved on fuel vs. time wasted driving economically, I've given up caring about fuel economy. At best you will save £1/hr. I'd rather have the pleasure of making swift progress and the reward of spending 10 mins doing something else than save £1/hr by driving slowly.

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04 Nov 2018 13:44 #197297 by Caelite
I've found with my VVT mpg drops off somewhat when you cruise above 3500-3800rpm, which is where the VVT cams kick in. Have actually experimented over a few 100miles and found a 2 even 3mpg difference between sitting at 60-65 and sitting at 70-75. Although some of this is likely attributed to the Jimnys aerodynamic profile.

I also find the car is far more planted at 65, at anything over 70 it is easily upset by crosswinds and overtaking wagons. That being said I don't have a steering damper and my shocks are knackered.

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04 Nov 2018 19:25 - 04 Nov 2018 19:27 #197308 by Scimike
Assuming your engine is in good order keeping the revs high is unlikely to improve the mpg. True during acceleration higher revs will use less fuel than a laboured foot to the floor acceleration, but once upto speed low revs and a light throttle are best. The Jimny aerodynamics dont help at speed, so light throttle and low rpm (below 4000) appear to be the best.
I am an old fart so just plod around well below 4000 rpm and get an average of 36.2 mpg. Best I have seen is 39mpg on a long run @50mph, worst is 32mpg after a thrash across the moors, revving the nuts off it.
Is it worth bothering about
no not really. Just drive it how you want and enjoy your Jimny.

If this mpg is an issue for daily you have the wrong car, my old C1 achieved 56mpg around town, a better option than a Jimny if you want cheaper fuel bills.

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Last edit: 04 Nov 2018 19:27 by Scimike.

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05 Nov 2018 05:06 #197313 by Lambert
A Jimny is very often a second or fun car not a super economical but dull as ditch water commuter, it is there to be enjoyed. The thing is that petrol is cheap, use it up and buy some more and have a laugh.

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