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Old 10th February 2011, 00:07   #16
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Default re: RPM shoots up when changing gears

I have the same issue in my ford Ikon 1.6 . There are two ways to solve this problem.

1. Stop the engine and start again.
2. If that doesn't work, disconnect the battery for 5 minutes and connect it again.. This will solve the problem.


If the problem is still there, consult a ford service center. They will apply some oil below accelerator pedal to solve this problem. If clutch is worn out, this problem will arrive very often.
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Old 10th February 2011, 00:35   #17
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Default re: RPM shoots up when changing gears

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Originally Posted by oxyzen View Post
... I have a feeling that this is not good for engine braking.
An increase of 100-200 revs/min should not affect engine braking. As downshifting raises the RPM much more than this.
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Old 10th February 2011, 20:04   #18
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Default re: RPM shoots up when changing gears

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Originally Posted by dhanushs View Post
An increase of 100-200 revs/min should not affect engine braking. As downshifting raises the RPM much more than this.
Normally it should go down by 200-300 RPM.
So isnt a difference of 500 RPM good enough to reduce engine braking.
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Old 10th February 2011, 21:50   #19
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Default re: RPM shoots up when changing gears

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Originally Posted by dhanushs View Post
An increase of 100-200 revs/min should not affect engine braking. As downshifting raises the RPM much more than this.
But would'nt it be bad for the clutch? Hope these things do not occur frequently. It happens in my Santro Xing, but I doubt it is Drive by Wire.
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Old 14th February 2011, 19:52   #20
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Default re: RPM shoots up when changing gears

The Altis suffers from the worst Rev Hang caused due to the DBW. It's a royal pain.

It takes time to get used to it and once your used to it, it's a pain to drive a car without DBW.

The DBW tries to make it easier to shift. When you let go off gas and press clutch it increases rpm's then it keeps it there. The rpm's drop after a while. This lets you slot into the higher or lower gear without having to rev match. So while upshifting or downshifting you use the clutch and no acc pedal to match the rpm's.
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Old 14th February 2011, 20:03   #21
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Default re: RPM shoots up when changing gears

Well, I have noticed the same thing in my Swift (K-Series).
As many has pointed out, this is the "Rev hang" caused by Drive By Wire. Essentially, ECU keeps the engine on boil a bit longer than you lifting the foot off the throttle.

I believe this is done to prevent the Car from jerking when you keep on-off throttle, especially during start-stop traffic. Of course more experienced drivers don't need this. But the torque vehicles will need this to keep less experienced drivers from bouncing the passengers around and/or giving extra workouts to the seat-belts
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Old 16th February 2011, 16:03   #22
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Default re: RPM shoots up when changing gears

i think it irrespective of the type of throttle drive by wire or the normal way. when accelerating the load on the engine is transferred to the wheels by the clutch, when depressing the clutch the load gets cut or the engine is free of the load which in turn increases the rpm by a couple of 100s. this difference will be minimal during sedate driving. but try in brisk driving the rpm increase will be considerable.
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Old 16th February 2011, 17:08   #23
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Default re: RPM shoots up when changing gears

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Originally Posted by Jump Start View Post
i think it irrespective of the type of throttle drive by wire or the normal way. when accelerating the load on the engine is transferred to the wheels by the clutch, when depressing the clutch the load gets cut or the engine is free of the load which in turn increases the rpm by a couple of 100s. this difference will be minimal during sedate driving. but try in brisk driving the rpm increase will be considerable.
The engine RPM will increase ONLY if fuel is supplied.

I believe you are mentioning the inertia of the flywheel?. If so, for this to happen you will have to have a really heavy flywheel revving at very high rpm's.

I don't think this is the case in engines of size <1.5-2
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Old 22nd February 2011, 07:12   #24
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Default re: RPM shoots up when changing gears

Hi guys! Sorry i was out of town and my internet was also kaput, so I wasn't here much!

I only took an example of 1300 rpm. I don't really see at what rpm I shift! I'm sure it'll be more on the 1.6 S since its pretty rev happy!
I just noticed that it happens only upto 3rd Gear, after that it doesn't seem to happen.
However, I do not consider it as a result of wrong clutch operation or acc pedal pressing during gear change, since it happens some what like it has been programmed!
The car is new, 4 months, 5800 kms. So, I guess this phenomenon isn't a problem, but a feature. But I will look out for some answers and get back ASAP.
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Old 27th February 2011, 20:14   #25
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Default re: RPM shoots up when changing gears

Hey Guys,

I have been observing this on my swift petrol too, It happens each time I change gears, I depress the clutch completely and I see that rpm zoom up a little and as soon as the clutch is engaged after the gear change the RPM comes back to lower than where I depressed the clutch to change the gear.

I may be wrong, but my theory of why this happens could be, when the clutch is engaged, the engine has the load of the car, so for example if the rpm is around 2200 and when I press the clutch the load from the engine is released and hence the RPM shoots up and then comes back down after the gear change / clutch release.
I feel this is normal. I may be wrong, any inputs are welcome.
I would also like to know if anyone else is facing such issue with their swift petrol (1.3).

Just to add -
The clutch on my car is brand new (2 weeks / 300 kms old)
I do not keep my foot on the accelerator when changing gears.
I depress the clutch completely before gear change.
I release the clutch and pump in gradually.

Please advice, if there is something that I need to be worried about.
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Old 28th February 2011, 18:08   #26
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Default re: RPM shoots up when changing gears

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Originally Posted by oxyzen View Post
I have a feeling that this is not good for engine braking.
Quote:
Originally Posted by oxyzen View Post
So isnt a difference of 500 RPM good enough to reduce engine braking.
You bet it is. The first car I experienced this in was the Opel Astra (did it have DBW???). I hated the revv hang in that car and had to adapt my driving style around it (lesser engine braking).
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Old 28th February 2011, 18:49   #27
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Quote:
Originally Posted by gearbox View Post
Hey Guys,

I have been observing this on my swift petrol too, It happens each time I change gears, I depress the clutch completely and I see that rpm zoom up a little and as soon as the clutch is engaged after the gear change the RPM comes back to lower than where I depressed the clutch to change the gear.

I would also like to know if anyone else is facing such issue with their swift petrol (1.3).
Hey gearbox,

Have noticed similar issue with my Swift Petrol 1.3 mostly on a long drive or while spirited driving. Well in my case, i really like this feature/issue as there is no need of manual rev matching while changing gears.(specially while driving hard)
But would really like to know if this is causing any damage to the sprinter.
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Old 28th February 2011, 20:39   #28
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Default re: RPM shoots up when changing gears

If you are not forgetting to close the throttle comepletely while shifting, this is what i think is happening.

i havent worked on gasoline systems, but i gues they will be similar to diesels which i am a little familiar with.
drive by wire cars do not use the raw input of the throttle for fuelling. the throttle sensor or (TPS) does give the ECU input on the instantaneous position of the throttle pedal. this input is processed or 'filtered' by the ECU / ECM processor using PID (proportional-derivative-integral) control logic. this refined input gets referred to in the fuelling curve.

take a case when the throttle goes from 0% to 100% in say 0.3 seconds. That cannot be the same rate at which fuelling can be increased from idle to full throttle. so fuelling increases gradually in a progressive manner. and usually follows a reverse exponential curve. hence it would reach from minimum to maximum in something like 1.5 or 2 seconds, or even more if some other correction map restricts it to anything of lower value.

similar is the case when the throttle closes. the closure can happen much earlier if we just move the foot sideways to our right and just let the throttle snap back. if fuelling reduces at the same rate, the engine would stall. so it must be reduced gradually.
so when you change gears, generally you would snap the throttle close and depress the clutch.
This removes the load off the engine and makes it rev up.

hope this helps.

nitro
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Old 28th February 2011, 23:44   #29
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Default re: RPM shoots up when changing gears

Quote:
Originally Posted by nitrogary View Post
take a case when the throttle goes from 0% to 100% in say 0.3 seconds. That cannot be the same rate at which fuelling can be increased from idle to full throttle.
Why this can not be the same rate at which fueling is increased? Manual throttles do it. Dont they? What is the advantage of increasing fuel gradually?

Quote:
Originally Posted by nitrogary View Post
similar is the case when the throttle closes. the closure can happen much earlier if we just move the foot sideways to our right and just let the throttle snap back. if fuelling reduces at the same rate, the engine would stall. so it must be reduced gradually.
How can the engine stall when you are around 2000RPM? And if the engine reaches idle RPM (In case you take years to shift) optimum A/F ratio for idle will be maintained. Thus no stalling. (Manual Throttle body)
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Old 1st March 2011, 00:05   #30
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Default re: RPM shoots up when changing gears

I also have same "revv hang" effect on my Santro Zip Drive. If i press clutch to change gear , it just roars if you are not releasing it really fast, I enjoy that mode but my father doesn't, so he checked with Hyundai Service they asked him to replace something near the ECU, Fuel mixing area which will cost 4k. Didn't replace it as of today, since i found a workaround to get away with the issue. Stop the car Just switch off the engine for few seconds then start, everything works normally after that for few hundred Kms.
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