Hissing sound from engine and varied idle rev's

T

Tasty

Member
Hi there

I wondered if anyone has had a the above problem. I have a nearly 6 year old Z4 with 88000 miles on the clock. The hissing sound stops 5 seconds after the engine has stopped running. Any ideas? I have rang AA Home Relay to come out and see if it is safe to drive the car.

Thanks
Tasty
 
Unfortunately not a hose loose! My mechanic had difficulty finding the airleak and had to strip the outlet trunking and perform a smoke test (apparently baby oil burns with a white smoke and also smells nice :D).

The smoke test found that it was the DISA valve that had broken. The specific element of this part that had broken was the air adjuster valve which fits in the centre of the inlet manifold and adjusts effective length of the inlet tract thereby improving torgue. The AAV was a hollow spindle made from a flimsy yellowpiece of plastic that had broken and was letting air in. There was a significant amount of carbon that had built up around the black plastic valve which probably helped break this spindle. He game me the part so I could see the issue at first hand. The part cost £131 including VAT which hurt, my mechanic was quick to find the problem and only charged me £80 for investigation and fitting (AJ Robinson, Brighton).

After AJ had spoken to the BMW local dealer (3 garages) he was told that they had never had this problem before. The part has also now been modified.

I have had the car since the launch in June 2003 and have done 90,000 miles so hope I am not a trailblazer on problems for aging Z4's.

Cheers
 
Is this the same part as what blew another owners manifold up?

http://www.z4-forum.com/forum/viewtopic.php?f=3&t=10372

Pictures would be handy of the bit that was bunged up and failed, as in the post above the owner was told it was a common fault!?


Really interested in looking at mine as it seems to be the 60-80k miles age when it might start to cause problems!

Manifold tuned intake flap thingy (number 7):
http://www.realoem.com/bmw/showparts.do?model=BT52&mospid=47797&btnr=11_2879&hg=11&fg=40

Part that other member had blow up (number 1):
http://www.realoem.com/bmw/showparts.do?model=BT52&mospid=47797&btnr=11_2194&hg=11&fg=15

Are these related as part of the same breather system!?

Thanks

Dave
 
Hi Dave

The whole orf the adjuster unit was replaced. The yellow spindle which twists the valve open and lengthens the air duct was the item which broke and allowed air to escape. If you remove the adjuster valve and clear the carbon deposits away this will probably stop the brake from occuring and a nasty £200+ bill.

regards
Tasty
 
I cannot see it making such an explosion as with the original post. I will upload photo's later as I have the broken part from the mechanic.

Cheers
T
 
Hmmm, something on mine is certainly on it's way out here, as the ticking has become louder recently.

Ran the car at idle, unplugged this device on/off and the rattle came and went away.

Plugged in, the shaft pushed out (closing the plate I guess), unplugged, the noise went away (ticking), and the shaft came back into the pushing unit (towards back of engine)...

Pressing down on the pushing shaft made it quieter a bit.


I guess this is a vacuum control solenoid, and it simply oscillates to maintain the valve closed state (seems to spring open by default, so ticking when at idle as it closes up).


Could do with removing all this and cleaning. Anyone taken this off before?!

I have a non-BMW warranty, so might take the car to get checked over, just hope that they recognise the fault and then advise a fix!

Cheers

Dave
 
Hmmm, this device has a standalone pump, or vacuum (probably vacuum), that runs to operate the flap in the manifold.

I think it is my pump that is making the ticking... clearly done enough cycles now to be on it's way out. Odd that this flap defaults open, since the duty cycle of the pump would be many factors less if it operated the other way around, as you rarely spend much time over 4000rpm vs time below it.

Anyway, it seems like an all-in one unit, so a replacement seems the best way to resolve. Might find a low-mileage breaker one :)

Dave
 
Mr Whippy said:
Hmmm, this device has a standalone pump, or vacuum (probably vacuum), that runs to operate the flap in the manifold.
I think it is my pump that is making the ticking... clearly done enough cycles now to be on it's way out. Odd that this flap defaults open, since the duty cycle of the pump would be many factors less if it operated the other way around, as you rarely spend much time over 4000rpm vs time below it.
Anyway, it seems like an all-in one unit, so a replacement seems the best way to resolve. Might find a low-mileage breaker one :)
Dave
Click to expand...

talking to OCS motorsport this weekend thay are regularly changing these units not as once they become rattly they are on the way out and could cause internal damage to the engine. They said that mine wasn't too bad, but I keep hearing it now when the roof is down and I'm becoming paranoid, so a new one will be ordered next week...
 
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