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Old 21st February 2017, 17:04   #1
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Default Jerkiness due to fuel cut-off?

Hi gurus,

i have this peculiar problem with current crop of fuel injected cars , especially the wagon- r 1.0 L K- series. In the quest for maximum efficiency, when we lift off the throttle, the fuel supply is cut off , which is great for mileage. But the moment it slows down to middling speeds and we get on the throttle, there is a jerk as the injectors switch on.

This combined with the inherent 3 cylinder vibrations, make you and the others in the car think that you still have a long way ahead to learning driving.

So my point is , is there any way we can disable this fuel cut off on over-run? I don't care about mileage , i need a smooth drive in city, not some eco-minded loony ecu instructing me when to cut off the fuel for which I HAVE PAID !!

Is it a switch we can simply pull out or we have to go into the muddled alchemy of ECU tuning?

Help !
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Old 21st February 2017, 17:18   #2
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Default re: Jerkiness due to fuel cut-off?

Quote:
Originally Posted by Nanolover View Post
Hi gurus,

i have this peculiar problem with current crop of fuel injected cars , especially the wagon- r 1.0 L K- series.
=============
Is it a switch we can simply pull out or we have to go into the muddled alchemy of ECU tuning?

Help !


You should not be feeling the injectors starting to work again.
I do believe it is not the injectors you are sensing but something else that jerks. And no, I dont think you can turn this off.

Last edited by Jaggu : 21st February 2017 at 17:32. Reason: Please avoid Quoting entire large post for short reply. Thanks.
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Old 21st February 2017, 17:40   #3
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Default re: Jerkiness due to fuel cut-off?

Second mayankk, ideally such transitions should be fairly smooth and one should not feel any apparent snatch while slowing down or while accelerating away. Unless it is sudden acceleration OR a wrong gear the vehicle is in.

If it is an old vehicle you might want to check the engine / gearbox mountings, injector / throttle body functioning to rule out issues, these are common reasons for such jerkiness while accelerating.
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Old 21st February 2017, 18:15   #4
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Oh, one other thing. To what revs do you drop before you touch the accelerator?
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Old 21st February 2017, 22:26   #5
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The fuel cut - off in over run is more of a safety and emissions related feature than for mileage. Of all ECU controlled cars I have driven till date, I have never encountered the mentioned problem, unless the over run is long enough for engine speed to settle at near idling speed.
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Old 21st February 2017, 22:39   #6
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Default re: Jerkiness due to fuel cut-off?

Quote:
Originally Posted by Jaggu View Post
Unless it is sudden acceleration OR a wrong gear the vehicle is in.

If it is an old vehicle you might want to check the engine / gearbox mountings, injector / throttle body functioning to rule out issues, these are common reasons for such jerkiness while accelerating.
Quote:
Originally Posted by mayankk View Post
Oh, one other thing. To what revs do you drop before you touch the accelerator?
You guys have asked the questions which I had in my mind as well. Well, my old Chevy Spark also had bad throttle response @ lower rpms in city traffic. But when I tried Shell fuel and after few top ups, the response was better.

So you could try different fuel, mechanical stuff as Jaggu as mentioned.
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Old 21st February 2017, 23:45   #7
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Default re: Jerkiness due to fuel cut-off?

I think what has been referred to in the opening post is nothing but the poor grunt at low RPMs which is a characteristic of 800 - 1000cc petrol engines. This 'jerky' feeling comes to the fore in creeping b2b traffic where the RPM falls below 1500 even in first gear with constant switching between the ABC pedals.

Not much can be done except for a bit of clutch riding to smoothen the transition which I do not like out of compassion for my clutch set.
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Old 21st February 2017, 23:53   #8
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Default re: Jerkiness due to fuel cut-off?

I believe you are experiencing the phenomenon known as inertia combined with lifting off at higher revs, engine braking kicking in and then engine getting on the boil again. AS such we cannot give you much advice without knowing how you are driving tbh
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Old 22nd February 2017, 00:27   #9
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Exclamation re: Jerkiness due to fuel cut-off?

Quote:
Originally Posted by Nanolover View Post
I have this peculiar problem with current crop of fuel injected cars, especially the wagon-r 1.0 L K- series.
In the quest for maximum efficiency, when we lift off the throttle, the fuel supply is cut off, which is great for mileage.
But the moment it slows down to middling speeds and we get on the throttle, there is a jerk as the injectors switch on.
It's not a "peculiar problem", pretty much all ECUs are programmed this way.
Have you looked at the data using an ECU reader or is this your theory regarding the "jerk" ?
For example :
- In my 2001 Alto, the fuel-cut-off on the overrun is disabled once the engine RPM drops below ~ 1,700.
- In my 2010 Alto, the same happens once the engine RPM drops below ~ 1,200.
In both cases, since the throttle is still closed, the IACV is activated too.
Quote:
Originally Posted by Nanolover View Post
Is there any way we can disable this fuel cut off on over-run ?
I don't care about mileage, i need a smooth drive in city, not some eco-minded loony ecu instructing me when to cut off the fuel for which I HAVE PAID !!
Is it a switch we can simply pull out or we have to go into the muddled alchemy of ECU tuning ?
Do note that when you have your foot off of the accelerator, the throttle is closed, hence there is little or no airflow into the engine anyway, if you have no fuel-cut-off on overrun you'd just be wasting fuel.
That said, if you can find somebody to decipher the ECU's engine maps, I guess you could try & raise the RPM at which the overrun fuel-cut-off is disabled.
You'd also have to activate the IACV appropriately, but you would lose engine braking earlier ( which I find very disconcerting ) & your car will behave like its diesel-engined.
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Old 22nd February 2017, 08:30   #10
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Default re: Jerkiness due to fuel cut-off?

Hi, yup had the same probelm in the alto vxi 1.1 also.

I guess my problem lies in the transition zone. For eg ; once i am coasting , fuel is cut off as per ecu and the if i press the accelerator before the engine falls into the overrun disabling zone ( say 1700 rpm). this is where the jerk is experienced. Maybe i feel it more due to inherent imbalance of the 3 cylinder engine amplifying it.

In many autocar india road tests also they have complained about the jerkiness of the throttle in city conditions for the 1.0 K series.

Any ways to smoothen this without affecting engine breaking? maybe a switch to K& N filters or better NGK spakplugs?

Also now that wagon-r is nearing 30 K, makes sense to change the engine mounts also.
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Old 22nd February 2017, 09:58   #11
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Default re: Jerkiness due to fuel cut-off?

Quote:
Originally Posted by Jaggu View Post
If it is an old vehicle you might want to check the engine / gearbox mountings, injector / throttle body functioning to rule out issues, these are common reasons for such jerkiness while accelerating.
Yeah, even I feel that it has something to do with the engine/gearbox mountings. The reason being - when we have our foot off the accelerator, engine braking comes into action and when we press it again, the throttle opens and there's smooth flow of air into the engine + injectors start to inject fuel into the engine. So this switch from braking to acceleration accompanied by worn out mounts might be the culprit here.

I too have observed this in my Santro. But recent cleaning of throttle body and the IAC has improved things a bit.
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Old 22nd February 2017, 10:19   #12
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Default re: Jerkiness due to fuel cut-off?

P.S : forgot to mention, it is not an old wagon- r . it is a 2 year old one with 30 K on the clock.
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Old 22nd February 2017, 10:25   #13
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Default re: Jerkiness due to fuel cut-off?

Quote:
Originally Posted by Nanolover View Post
Hi gurus,

i have this peculiar problem with current crop of fuel injected cars , especially the wagon- r 1.0 L K- series. In the quest for maximum efficiency, when we lift off the throttle, the fuel supply is cut off , which is great for mileage. But the moment it slows down to middling speeds and we get on the throttle, there is a jerk as the injectors switch on.

Help !
Check your clutch - maybe its worn out. This kind of jerk is common occurence on cars with worn out clutches.
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