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Old 19th December 2008, 12:50   #1
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Default Unwanted RPM surge with my Dzire VDi

Hi All T'bhpians,
Had a question. Hope you all can help me with the same.
Background: I bought a Dzire VDi approx a month back. It has gone approx 900Kms till now and I would be giving it for the first service next week.
I have been noticing something from day one and it has been bothering me. I will try and explain the same:

Issue:The main issue I have seen is that if I downgrade from a higher gear to a lower gear, I notice a RPM surge which I can see clearly in the RPM meter. For e.g. If I am driving in 3rd at approx 35 kmph and need to brake and move to second, the moment I engage the clutch, I see a momentary surge in rpm to the tune of approx 200 rpm and then it decreases. Sometimes the surge is to the tune of approx 500 rpm and then it comes down especially if I am coming dowm from a high gear like 4th or 5th down to second or third.

Also I have noticed that in the first two gears, pretty much till I reach approx 20 kmph I dont even need to press the accelerator. I believe it might be set a little high from the company as the car is new. Can this be the reason for the momentary RPM surge.

Your valuable inputs would be highly appreciated.

Thanks
f1fan
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Old 19th December 2008, 13:17   #2
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Almost all ECU driven cars will pump in a little extra fuel into the engine when you go on the clutch, but that it not enough to get the RPM up by as much as 500 RPM. I don't think this is any cause for worry.

Also try a small experiment. When down shifting, make sure your right foot is completely of the accelerator and then press the clutch pedal and see if this still happens. I think you are going on to the clutch a little earlier than lifting your foot of the gas pedal.

Edit: I have a diesel swift as well and have not noticed this on my car.

Last edited by vikram_d : 19th December 2008 at 13:19.
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Old 19th December 2008, 13:45   #3
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Quote:
Originally Posted by vikram_d View Post
Also try a small experiment. When down shifting, make sure your right foot is completely of the accelerator and then press the clutch pedal and see if this still happens. I think you are going on to the clutch a little earlier than lifting your foot of the gas pedal.
That was my first thought too but checked it without my foot nowhere near the gas pedal but still the same result.
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Old 19th December 2008, 13:48   #4
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Quote:
Originally Posted by f1fan View Post
That was my first thought too but checked it without my foot nowhere near the gas pedal but still the same result.
In that case wait for first service to get over and see if this behavior persists. If it does then get it checked by a competent service station.
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Old 19th December 2008, 14:07   #5
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Quote:
Originally Posted by f1fan View Post
Hi All T'bhpians,
Had a question. Hope you all can help me with the same.
Background: I bought a Dzire VDi approx a month back. It has gone approx 900Kms till now and I would be giving it for the first service next week.
I have been noticing something from day one and it has been bothering me. I will try and explain the same:

Issue:The main issue I have seen is that if I downgrade from a higher gear to a lower gear, I notice a RPM surge which I can see clearly in the RPM meter. For e.g. If I am driving in 3rd at approx 35 kmph and need to brake and move to second, the moment I engage the clutch, I see a momentary surge in rpm to the tune of approx 200 rpm and then it decreases. Sometimes the surge is to the tune of approx 500 rpm and then it comes down especially if I am coming dowm from a high gear like 4th or 5th down to second or third.

Also I have noticed that in the first two gears, pretty much till I reach approx 20 kmph I dont even need to press the accelerator. I believe it might be set a little high from the company as the car is new. Can this be the reason for the momentary RPM surge.

Your valuable inputs would be highly appreciated.

Thanks
f1fan
Hi F1fan,

Welcome to the power/Torque of DDIS engine. DDIS has 190 NM of torque which is driving your car even without pressing accelarator in gears 1 and 2. This is normal.

The engine behavior of RPM surge also seems normal to me. This will reduce over time not to worry. You need to get adjusted to driving a Diesel car especially DDIS.
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Old 19th December 2008, 14:14   #6
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same speed results in different RPMs in different gears. its possible that you are downshifting at a higher speed.

the next time you drive your car, note down the speeds at 1000 and 2000 RPMs in each gear. then at each gear upshift at 2000rpm (while accelerating) and downshift at 1000rpm (while slowing down).

assume 40kmph in 3rd gear produces 2000RPM and 20kmph in 2nd gear also produces 2000rpm.

in this case while upshifting from 2nd to 3rd if you do it at 20kmph it would decrese from 2000 to 1000 in 3rd.

similarly while slowing down from 40kmph, do not downshift until 1000rpm (20kmph). when you downshift at this point, you can see the rpm at 2000 in 2nd gear. keep slowing down (using engine braking or pressing the pedal) and you can see the rpm reduce rapidly.

maybe 35kmph is too fast for 2nd gear, hence the high rpm.

i think what you are facing is not a problem but a feature of a torquey diesel engine! is this your first diesel car?
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Old 19th December 2008, 14:28   #7
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Atleast in my DDIS, when I let the car slowdown till the rpm drops to about 1000 rpm or lesser and then press the clutch, the rpm increases. I think this is because the ecu suddenly has to adjust to the engine not propelling any load and correspondingly reduce the fuel being pumped in. This might take a second or two during which time the rpm increases.
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Old 19th December 2008, 14:39   #8
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I have come across this while driving my relative's Dzire VDi.

What i noticed is that the clutch is kept little steep to reach and due to this - i had some minor problems during gear change (bringing the clutch to biting point) and sometimes over acceleration during gear change

Not sure how many of you guys felt the same.
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Old 19th December 2008, 14:45   #9
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Quote:
Originally Posted by CtrlAltDel View Post
maybe 35kmph is too fast for 2nd gear, hence the high rpm.

i think what you are facing is not a problem but a feature of a torquey diesel engine! is this your first diesel car?
I was just giving an example about 35 kmph. What I meant to say was that when I try to downgrade and press the clutch (irrespective of what speed I am doing) I see a small surge in the RPM.
Pls note that it is a momentary surge and within a couple of seconds comes down. If I downshift using a higher speed in a lower gear, the RPM would jump no doubt but would not come down till I slow down but in this case it is a momentary blip and then everything is back to normal.

Yup, This is indeed my first diesel but have driven diesels.

BTW I never encounter this while upshifting.

Last edited by f1fan : 19th December 2008 at 14:51.
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