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Old 22nd July 2008, 12:31   #1
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Default does MPFI jerk when revved at idling ?

guys i just observed a strange phenomenon.
i have an alto 800 cc and today it just happened that i revved my car to high rpms in idling mode. i found that the engine gives a strange jerks and misfires at high RPM as if one cylinder fails to fire.

i went to M.A.S.S and they said that it happens in all MPFI cars and henceforth i shouldnt rev the car in idling as the catalytic converter gets damaged. he also showed me another alto in which the same thing happened.

i think that the exhaust gases get trapped in the catalytic converted and this jerks occur
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Old 22nd July 2008, 12:52   #2
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Doesnt happen in my M800 which is completely stock. Something is not right. Get a second opinion.

BTW i thought you got rid of the cat and opted for a FFE.
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Old 22nd July 2008, 13:10   #3
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doesnt happen in mine either its been long though that I tried something like this.
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Old 22nd July 2008, 13:12   #4
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Hi Amit, are you sure it's not just the rev limiter cutting in ?

At what RPM have you noticed this misfire ?
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Old 22nd July 2008, 13:20   #5
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Quote:
Hi Amit, are you sure it's not just the rev limiter cutting in ?
Bang on, this is the reason I believe
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Old 22nd July 2008, 14:41   #6
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Nope, I haven't experienced any mis-firing while revving in neutral. I've tried it in an OHC. It may mis-fire if the engine has not heated upto its operating tempature. Do not do this on a cold engine, never!!
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Old 22nd July 2008, 15:38   #7
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cant the exact RPM, but its quite high. till some extent of revs this thing doesnt happen at all but when u press the pedal to almost bottom you hear a sound " vroooom vrooom fadrrrrrr "

Vroom : smooth revving
Fadrrrr : at this moment the engine jumps the front of the car bounces once and the exhaust bangs a big stroke once.

the above continues till u dont leave the accelerator.

@ technocrat : can you confirm whether this happens with your alto?

just when the car is stationary press the accelerator to almost full and check whether there is jerk with the engine.

he showed me one more alto there which faced a similar but mild jerk.
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Old 22nd July 2008, 15:41   #8
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Me too thinks its the limiter cutting in.This just does'nt in 'idling mode' but also if the car is revved beyond a certain RPM in any gear.
The reason for the existance of this rev limiter is to protect the engine from being over revved and ultimately from something being blown to smithereens.
Its OK, no problem.
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Old 22nd July 2008, 15:42   #9
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Quote:
Originally Posted by n_aditya View Post
Doesnt happen in my M800 which is completely stock. Something is not right. Get a second opinion.

BTW i thought you got rid of the cat and opted for a FFE.
ya lots of things are trying me to indicate that i dont need the stock exhaust anymore planning for a 2 days trip to mumbai soon.
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Old 22nd July 2008, 15:43   #10
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As said it looks like the fuel is getting cut off when you hit the revlimiter.

Amit, its not good to rev the engine so much on idling. Do you feel the jerking when the car is being driven?

Quote:
Originally Posted by amit_mechengg View Post
Fadrrrr : at this moment the engine jumps the front of the car bounces once and the exhaust bangs a big stroke once.
Sounds like gas. Sorry Amit. couldn't resist.
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Old 22nd July 2008, 15:44   #11
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Quote:
Originally Posted by im_srini View Post
Hi Amit, are you sure it's not just the rev limiter cutting in ?

At what RPM have you noticed this misfire ?
how do i judge whether this is the rev limiter? how does rev limiter act?

actually this is happening only in neutral/ idling and not when i am speeds of 120 kmph.

i really dont know why all funny things keep on happening with my car.
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Old 22nd July 2008, 15:51   #12
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Quote:
Originally Posted by amit_mechengg View Post
how do i judge whether this is the rev limiter? how does rev limiter act?
Well if you have a tacho you can see the needle bouncing off the revlimiter. Since you dont have one, listen to the sound. Is it a continuous trrrrrrr, trrrrrrrr sound? If yes, then its the revlimiter you are hitting.

If the exhaust is blasting away once in a way like a firecracker, then the air/fuel mixture is not optimal. The engine is running too lean.
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Old 22nd July 2008, 16:14   #13
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ya now i guess its the rev limiter thats kicking in. its doesnt blast like the autos like a misfire.
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Old 22nd July 2008, 16:14   #14
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Quote:
Originally Posted by amit_mechengg View Post
how do i judge whether this is the rev limiter? how does rev limiter act?

actually this is happening only in neutral/ idling and not when i am speeds of 120 kmph.

i really dont know why all funny things keep on happening with my car.
Amit, a revlimiter as the name suggested limits the revs to increase beyond a certain RPM.

Do one thing, Rev your car in first gear, it should start jerking around 35-40kph & similarly on 2nd around 75-85kph.

Its perfectly normal.

Also there is nothing wrong with your car, you are over cautious thats all
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Old 22nd July 2008, 16:20   #15
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Quote:
Originally Posted by Technocrat View Post
Amit, a revlimiter as the name suggested limits the revs to increase beyond a certain RPM.

Do one thing, Rev your car in first gear, it should start jerking around 35-40kph & similarly on 2nd around 75-85kph.

Its perfectly normal.

Also there is nothing wrong with your car, you are over cautious thats all
ya i will surely try this. even aditya suggested me the same.

Yes perfect, even the service station people say the same, i am overcautious
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