For my sins, I own an 03 plate Fiesta 1.6 Zetec and its just failed its MOT on massively high CO levels in its emissions.

Looked under the bonnet and there is a hissing air noise coming from somewhere on the right-hand side/right-hand front of the engine block; coupled with this, when I stamp on the accelerator, I get what sounds like a sudden intake/pop/suck of air which is not too dissimilar to a dump valve sound (and I ain`t got one of them!).

I`m thinking it's taking air into the cylinders from somewhere other than the normal routes; could this effect the CO emissions to such a great extent and how could I diagnose and repair??

Cheers, James.

For my sins, I own an 03 plate Fiesta 1.6 Zetec and its just failed its MOT on massively high CO levels in its emissions.

Looked under the bonnet and there is a hissing air noise coming from somewhere on the right-hand side/right-hand front of the engine block; coupled with this, when I stamp on the accelerator, I get what sounds like a sudden intake/pop/suck of air which is not too dissimilar to a dump valve sound (and I ain`t got one of them!).

I`m thinking it's taking air into the cylinders from somewhere other than the normal routes; could this effect the CO emissions to such a great extent and how could I diagnose and repair??

Cheers, James.

sounds like you have a vacuum leak, check all the hoses/pipes for splits or damage.

sounds like you have a vacuum leak, check all the hoses/pipes for splits or damage.

Checked for splits/bad connections and found nothing; however the source of the sudden air suck - took the air filter box and pipe off of the throttle and found the noise to be coming from the inlet butterfly valve on the throttle unit. It`s almost like its gasping for as much air as if can get in and is more violent the faster you press the loud pedal....