Turbo whine

My friend has bought an 09-plate Ford Focus ST which has a couple of issues. First, there’s a notable knock from the gearbox end of the engine which stops with the clutch down. What’s the likely culprit: DMF, clutch or transmission?

My friend said the car has been remapped. It has a cone-type induction air filter under the bonnet – sucking in all the hot air, I guess – and an atmospheric dump valve and a de-cat pipe which is going to be replaced with a cat, so there’s a good chance it has been remapped and producing a lot more torque. Am I right in thinking that DMFS are only designed for the OE engine specs?

There’s also a whine/whistle from the turbo as it spools up, which can be heard from inside the car. This sounds suspicious to me, but I’m not familiar with these engines so I don’t know the norm. Anthony Pattinson

The knock from the gearbox end is most likely to be the DMF, but it is difficult to say without hearing it. Short sharp revs of the engine will normally show up a DMF noise, which will knock as the revs increase.

The re-map has probably been necessary due to the removal of the standard air filter system and fitting of the de-cat. This is a point that will get picked up at the next MOT and will need rectifying. When the cat is refitted, the ECU will have to be readjusted.

The whine/whistle may be due to the dump valve or the cone filter – both can alter the pitch of the turbo. It could also be that the turbo bearings are failing and the rotor is making contact with the interior of the turbo duct. You can check this by looking in the turbo for any shiny marks, indicating that contact has taken place. If any contact is taking place, or if any movement can be felt in the shaft, the turbo will need to be renewed.