Turbo sound
 

I think i have got a leak somewhere in my exhaust system( probably the exhaust manifold is cracked. When i release the gas pedal ( after a quick acceleration) i hear a turbo sound ( pssiiiww) . Do you think that the sound is related to the exhaust leak ? ( my x is also louder than before)

If your exhaust manifold is cracked you will have a lot more noise than when it is intact, I would start there.

ECS Tuning

Do you have 3.0d? It's quite common to have a crack in exhaust manifold in these. They start to whistle especially under acceleration and also loose some low end torque.

2001 4.4 . Everything is normal ( power torque ) but the sound is louder than before. But if the manifold is cracked i think that o2 sensor should find the problem?

Ahh... why didn't I pay attention to you nick, that should have told me already that we are talking about V8's here :D.

This cracking manifold problem is specific for 3.0 diesels. It shouldn't affect the O2 readings that much but it looses some pressure and turbo doesn't fully kick in until you get to the higher revs. Your 4.4 turbo is aftermarket and I'm not that familiar with those, sorry.

My mpg is very poor . Do you think that it is related to the cracked exhaust?

Forgot to say That im getting also a rumble noise from under the car