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Engine Tuning

  • Hugo
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23 Mar 2019 11:41 #204950 by Hugo
Engine Tuning was created by Hugo
I have a 2001 Jimny soft top with the original 16v engine. Only had it a few weeks and have changed the cambelt and tensioner and given it a good general service including plugs. The problem is that is running a little lumpy and drinking petrol like 3.0l, I am getting no more than 27 mpg on the motorway (65mph @ 3750rpm), the engine takes 15 to 20 seconds to drop the revs back down to the idle tickover speed when pulling up at lights etc and the she coughs and splutters a little when restarting from warm. The carb side of things appears to be controlled by part e and part mechanical cable, so I guess it will need some kind of diagnostic testing if I take it to a main dealers. Does anyone have any ideas or experience they could share before I do shed out some of my hard earned? Thanks in advance,

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23 Mar 2019 23:21 #204982 by Max Headroom
Replied by Max Headroom on topic Engine Tuning
Hello Hugo and a BigJimny welcome to the forums.

Sorry to hear that you have some issues. I consistently get around 35 mpg with my convertible VVT and from what you describe with the rpm drop I think it is clear that you certainly have a problem of some kind.
I'm sure someone with more experience will be along soom that has some experience of these niggles, but I noticeably improved the performance of mine by fitting a K&N air filter. Is your air filter clean?


IF IT AINT BROKE, KEEP FIXING IT UNTIL IT IS

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  • Lambert
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24 Mar 2019 08:59 #204990 by Lambert
Replied by Lambert on topic Engine Tuning
Rev hang could be as simple as the throttle body needs a good cleaning. It's not unheard of for a varnish like accumulation to cause problems.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
ADOS Attention Deficit Ooooh Shiny!

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  • Hugo
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24 Mar 2019 11:05 #204995 by Hugo
Replied by Hugo on topic Engine Tuning
Many thanks Lambert, I’ll check the throttle body out on my Jimny.

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24 Mar 2019 11:08 #204996 by Hugo
Replied by Hugo on topic Engine Tuning
Thanks for the kind welcome. Yes, I have just replaced the air filter with a standard off the shelf replacement. I guess the K&N’s are available in the BigJimny online shop.

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24 Mar 2019 12:23 #204998 by facade
Replied by facade on topic Engine Tuning
Unless the air filter is solid with dirt, a K&N isn't going to make much difference.

It wants the diagnostics so that you are not just throwing money at it. If you want to punt money at it (probably a 50:50 shot), change the lambda sensor at the manifold, this controls overall fuelling, and when they go out of spec. you do get rich running, and the ecu thinks everything is awesome, as the sensor reading is "correct".

If the engine temperature reads low, the ecu will run it rich as it thinks it has a cold engine.
If the EGR valve is stuck open it will cause a rough idle and affect MPG, but I'd expect the engine light to come on.

On the other hand, 27MPG into the wind at 65MPH with off-road tyres would be good for a Jimny anyway.....

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)

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  • StatusRed
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26 Mar 2019 08:28 #205085 by StatusRed
Replied by StatusRed on topic Engine Tuning
Could be...

Spark plugs
Air filter
Throttle body dirty
Fuel pump

Worth checking all of these, maybe a vacuum leak even?

Do Jimny's have an in-line / serviceable fuel filter either? I assume not being petrol but if so, maybe worth checking.

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  • Lambert
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26 Mar 2019 09:18 #205088 by Lambert
Replied by Lambert on topic Engine Tuning
The filter is in the fuel tank and is not a service item. The pumps too are generally reliable.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
ADOS Attention Deficit Ooooh Shiny!
The following user(s) said Thank You: StatusRed

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27 Mar 2019 08:17 #205122 by kirkynut
Replied by kirkynut on topic Engine Tuning
I'd clean the throttle body by spraying carburettor cleaner in it, nothing else and don't poke anything in it to clean it, just spray.

If this makes no difference I would replace the idle control valve as it sounds like it is sticking and it cannot be cleaned.

Kirkynut

The underdog often starts the fight, and occasionally the upper dog deserves to win - Edgar Watson Howe.

My Jimny Thread Here: www.bigjimny.com/index.php/forum/8-my-ji...on-continues?start=0

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