Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - fffft sound on accelaration

With the roof down this afternoon I happened to notice a brief "fffft" sound emanating from the engine bay on each gear change when accelerating. Sounds like a sharp intake of air - very faint, never noticed it before but now my ears have tuned in to the sound it's becoming more noticeable. Is this normal? The "fffft" sound, that is.
Paul Bevan

I had a sound that made my TF sound a little like a VW beetle when accelerating, that turned out to be a leak in the exhaust downpipe I think.
Paul Lathwell

there is a technical reason, but I cant remember ... been a while.. but all MGF's and TF's make it .. it is air ... If you want me to elaberate ... I will need to phone a friend ... But I'm sure if you ask the audience they can tell you ... I remember anoying my mechanics over it :)
Mr E

Paul, it's nowhere near as prominent as the Beetle sound and I've not noticed any loss of performance or changes in fuel consumption so I'll go with Mr E's judgement on this one but keep an ear out just in case!
Paul Bevan

Mine did that too, prior to fitting a K&N (can't tell any more!)

Mentioned it when I took her to Techspeed recently for a damn good going over. They couldn't figure out what it was, but were pretty sure it wasn't anythng bad. I just left it at that!


Totally normal, I'm not sure what is but I have 3 guesses:-
When putting you foot down on the accelerator the ECU opens a bypass valve, the idea being that when you let off, the ECU slowly closes this to get a smooth idle and cleaner emmisions, this is called 'soft landing'. I was sure it was this until I thought that the pressure differential on each side of the IACV would be quite low at full throttle

The charcoal canister:
The petrol tank is vented (petrol expands quite a lot with heat, like day/night cycles), but to limit that petrol smell, and again for emmisions, the venting is thru some charcoal, the engine puts this under high vacume which sucks out the petrol, when the engine is running normally.

The throttle:
On carbs there is always a leak past the throttle plate, this is how idle is adjusted, on injection this is done by leaking air in a ECU controled way with the IACV, so you could just be hearing the seal of the throttle being broken, and air rushing past the narrow opening before the throttle gets wider and the air pressure can stabalize.
Will Munns

Will, a little over my non-technical head but my vote goes to your 3rd guess: The ffft can be heard when you blip the throttle fairly sharply when cruising,/changing gear - if you accelerate smoothly or blip the throttle when idling there's nothing...
Thanks to all for the reassurance.
Paul Bevan

Ok I rang a friend .. he said " For the last time its the Throttle butterfly air intake, you salesmen are all the same, now sod off I'm busy".

He added "The reason you can't hear it when there is a K&N on, is because they're so bloody loud"

I hope this helps
Mr E

option 3 then, I had a feeling it would be!
Will Munns

LOL nice one Mr E!!! :oD
Rob Bell

Paul Bevan

This thread was discussed between 29/03/2004 and 30/03/2004

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.