Knocking sound when rev hard / speed picks up

[Ixat]

Hi bros,

 

My ride is experiencing "knocking sound" when I rev hard and the car picks up speed.

 

If I rev in free gear, no knocking sound.

 

If shift normally at 2.5k for ever gear up to 110km/h its also smooth without the knocking sound.

 

Once I drop a gear, rev shoots up to 5-6k and car picks up speed, the knocking sound comes in. Recently changed to coilovers but had same sound before changing too.

 

Any idea bros?

 

BTW driving a Getz 1.6M.

[Aros]

Bro, As what i was told by the machanic the knocking sound is due to the octane not enough ,previous using 92 now switch to 95 n the sound is gone. hope this help

[Supercharged]

Bro, another thing u might wan to check is ur axle!!

My bro car last time also same problem - cause his axle wan to ker chiang liao!!!

hope dat helps!

[Ixat]

I'm using Esso/Mobil 95 at the moment. Initially also thought somewhere is out of breath or misfiring or simply pinging....hmmmm

[Ixat]

Hey bro, the knocking sound also sounds like metal hit metal but its "thud thud thud" and not "clank clank clank" if u know what I mean. Yeah so I'm also worried it could be the steering rack or like say axle...

[Beei]

1. axles or

2. tyre nuts loose

[York]

Time to tune up the engine...adjust to a slightly wider firing angle..

....or Just let ur mechanic noe the problem..he'll noe how to correct it.....

[Kyojin]

if it doesn't happen a high speeds with low revs (as you described), it's probably pre-detonation/engine knock.

 

it should sound like marbles being shaken in a Milo tin. but it could well be a case of noisy lifters.

 

but could be other problems too, drive shafts, wheel bearings. try driving with all your windows up, no air-con, no radio and listen carefully according to the RPM.

 

have you checked your coolant lately? are you overheating?

 

in any case, if it doesn't happen at high RPM, you should back off your accelerator IMMEDIATELY. if it's really pre-detonation, it will cause serious damage to engine.

 

since you have a coilover, what other mods have you done?

[Ixat]

Bro it does sound a little like the frequency of marbles shaken in Milo tin but more of a lower tone rather then "clink clink". Kinda like "tong tong tong"

 

I can maintain 120km/h at 3k rev and its smooth without any knocking. Once the gear drops and rev ups the sound comes in.

 

Even after I lift off the throttle, can see hear the knocking till the revs drops and car slows down.

 

Coolant is at right level and still looking green. No experience of overheating for this car.

 

Other than coilver, I have got a CAI done with a K&N filter. Filter hasn't been serviced for 40K but took it out and see and it looks ok. I was thinking the filter maybe restricting air flow thus knocking.

 

Overall power of engine is still the same throughout the revs/power band.

 

PS: Going to my mech tomorrow. Meantime pls continue to contribute so I can have a clearer picture when I go to my mech tml.

[Kyojin]

just tell ur mech the prob. he should be able to give you a diagnosis quickly.

 

in the meantime, keep your revs low. do not try to down shift from 5th to 3rd gear. the more you try, the more internal damage you are causing...

[Yeobh]

I am bit confuse with yr " Once I drop a gear, rev shoots up to 5-6k and car picks up speed" - if you shift gear downwards, the transmission will try to retard the engine rev - the result is a drop of engine speed.

When you rev hard - if yr engine is a distributor type , the vaccum adv mechanism will comes into action and advance the spark firing timing by as much as 7 to 10 degs.If this does not happen , you will not be able to rev the engine smoothly. Bas etiming is normally set for most cars @ 5 to 7 degs Before Top Dead Centre.

My conclusion is either the clutch bearing is going bad or the engine base timing is far too advance. When you have too much advance base tinmig setting, during acceleration the spark will fires almost when the piston is at its top dead centre - it's just too late for the spark to fire up the fuel. The actual combustion will happen when the piston has already near or pass TDC.The near or after TDC combustion will creat tremendous vibrations and knocking on the piston and crankshaft bearings.

 

Hope this helps

[Ixat]

Thanks for ur advise bro.

[Ixat]

Hi Yeo, I am driving Getz manual. Drops a gear and rev goes up. I hope I am understanding what you meant.

 

Also what you mention with regards to spark timing etc, does it also apply to when stationary and in free gear, and revving the engine? Cuz revving in such state, does not reproduce the knocking sound.

[Yeobh]

Frankly , it's very difficult to do virtual diagnosis, even with the car in front and with good maintance history reocrd and driver feedbacks - the professional mech still need to carry out tests with the right tools to get the infos before pinpoint the source of the problem. Sometimes the problem can created by multi sources- so one have to tackle one by one to elimate the minor from the major.

Sorry , I cannot be of much help .

[Ixat]

Just came back from my mech. Confirmed its not engine issue nor steering rack. Isolated it down to suspension. Either not enough grease or not enough damping between the damnper and the car chasis.

 

Above 4k rpm, every bump on the road will result in very pronounced "tong" sound. Below 4k rpm the sound is very very slight.

 

I can either live with it, or seek 2nd opinion...what do you guys think?

[Apollo]

if u hv just done ur timing belt it may b the cam outta alignment.

 

i am also not sure if the problem has anything to do with the ignition coil faulty/ distribution cable faulty/ plug misfiring.

[Ixat]

Bro in free gear, the engine revs very smoothly, only when gear engaged and moving fast over bumps.

 

Can I ask engine under load and engine without gear is very much different?

[Apollo]

i can only haphazard a guess betw electrical or mechanical fault.

 

dun think is the fuel octane level. if u hv EGR (exhaust gas recirculation) system in the car, check the EGR filter and EGR soleniod (cud b the latter)

 

how to know this is beri easy, just pop over bonnet, push hand to the EGR box, and other person rev the engine. u may b able to feel the thud in the filter box. this happens to me b4.

Edited November 3, 2007 by Apollo