Screeching sound under acceleration - 3.0d Sport

[spidey]

Hey Guys

I recently picked up a horrible screeching noise when I accelerate. The noise is similar to a slipping fan belt. I took it in and the mech seems to feel that it's a blocked Cat (come the think of it, the noise does sound like a cat in pain )

So, it's booked in next week to get the cats removed. Funny that it seems to be intermittent and there is no noise when the engine is cold. One suggestion was that it is harmonic distortion, meaning that the turbo may have been worked on and is hurt slightly - if this was the case though, surely I would have a constant noise?

Any ideas?

[pvr]

Blocked cat??? We don't have cats on the diesel ....

[spidey]

Apparently there are two - one below the manifold and one further down. SA version perhaps? I need to check.

[spidey]

Local Dealer confirmed 2 Cats

[X5Sport]

In all gears, or just one? Does it appear as soon as you apply power even before the engine speeds rise? Could be torque converter as well.

Could be water pump. Possibly turbo if the bearings are worn, but I'd expect you to see oil smoke if that was the case as well as a loss of power.

Some versions have twin cats - in the UK we don't. You probably have this lot.

http://www.realoem.com/bmw/showparts.do ... g=18&fg=10

Mine does have a cat, but only one - http://www.realoem.com/bmw/showparts.do ... g=18&fg=10 which was required to meet Euro III emissions certainly in 2005, dunno about earlier production years. Preferred option now is to replace with a DPF - which the E70 & E71 now have to meet Euro IV.

[spidey]

In all gears. there are times you hear it when you take your foot off the gas - sounds like a jet engine, which is better than when you accelerate. There's no loss in power that I can feel. The engine pulls like a train and seems pretty strong - 180km/h comes up in no time with power in reserve.

I'll ask Alec @ Evolution 2 to check out the various options and will post up diagnosis and cure when I find out. Decat will be done anyway.

[Black X5]

I'd put my money on a fractured exhaust manifold- especially if there is smoke from around tht area when the engine is revved (stationary, with bonnet open and a willing assistant) HTH.

[x555]

If it's a cracked manifold (and i hope it isn't for you) then as said above you will have smoke coming from under the bonnet and there would be a very strong exhaust fume smell.You can check the manifold for cracks with a small mirror and torch.

[spidey]

Thanks X555 - will do. I havnen't noticed the smell of exhaust fumes though, or excess smoke.