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MG MGF Technical - Maybe being stupid but...


I am recently noticed a hissing notice when pressing the accelerator. It happens when you first touch the pedal (more noticable over 3k) for about 1/2 a second. The sound is not unlike a dump valve in turbo'd cars but a bit quieter.

You can only really hear it with the roof down. Obviously sounds like a jet of air escaping from somewhere but don't know what or where.

Is this anything to worry about? Performance doesn't seem to be affected and it only happens when you first touch the accelerator.

CJ Uren

Hi ,
probably the coal canister being emptied of fuel vapour when You accelerate hard. Can usually be heard on cars with standard exthaust system ;)
Another thing could be the beginning of a small leak in the flexible portion of the exthaust system. Milage and age of car ?

BR, Carl.
Carl Blom

The car is an early 1996 MPi covered 65k.

The exhaust system and the engine is completely standard, my insurance company went ape went I suggested only a K&N to them.

CJ Uren

Mine does excatly the same thing
Will Munns

On a similar note, I've noticed with my VVC+K&N that when approaching a speed hump, if I leave the car in gear and clutch engaged while braking (e.g. in 2nd, revs ~ 2k) I hear a very noticable hiss/sucking noise. Always assumed this was K&N related but never understood why as at these revs there shouldn't be too much airflow...
John Pickup

John, in your case it might be air being pulled thru the butterfly valve or IACV, as the inlet plenium is at very low pressure because the valve is shut, however the noise I hear is exactly oposite to this.
Will Munns

This thread was discussed on 21/03/2003

MG MGF Technical index

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