Z4 3.0si N52 (facelift) hissing / performance issues

[David]

Going to be investigating today, and searching for a vacuum leak, as I'm experiencing the following issues:

• Strong petrol smell on start-up
• Hissing/Squirting noise can be heard on light acceleration
• MPG decrease
• Power decrease

The noise has been present for a while. Initially I thought it was just wind noise between the car body and the hardtop, as it is audible on the left side of the car, when sat in the drivers seat. But since removing the hardtop the noise has continued and worsened. This noise was also present before fitting my AFE cold air intake, but I will also inspect that for leaks.

I've been researching this over the past week, and it seems like I'm not the only one who has had this issue. Lots of others have taken their cars to BMW for this hiss, and all have reported that the techs have told them it's "just a characteristic of the engine", which I, along with others, fail to believe.

The noise can be heard in this clip, which is not my video, but the noise is identical:


https://youtu.be/TKskUA7H0PQ


And one of many a thread where people have experienced the same issue:

http://www.bimmerfest.com/forums/showthread.php?t=526444

People with a similar issue on the 3.0i M54 have resolved this by replacing the DISA valve gasket, which will be my first port of call along with inspecting all the hoses.

(From ZRoadster.org) @MAURICE THE MARTIAN had a similar issue recently which @Murray Wall helped him resolve. I'm hoping someone on here has had a similar experience with the later engine (N52)?

Any help/advice is much appreciated!

David

 

[David]

New I will be creating a couple of new gaskets on the cold air intake, using this stuff I found on Amazon:



It's primary use is in hospitals for non slip surfaces, as it's non toxic/antimicrobial, so I figured it should create a good seal. Hopefully there won't be any issues with heat of the engine.

I am also armed with an o-ring set, so I won't have any issues sourcing the correct size o-ring for the DISA valve seal.

 

[David]

Update:

Inspected the DISA valve and the seal looks in good nick, so I have left that as is, and eliminated that from the list of suspects.

There was a bit of oil inside the inlet manifold, which I've been told is normal (...anybody?)

Also refitted the the cold air intake, added gaskets, and an o-ring to the MAF sensor. Also made sure all the jubilee clips were tight and seated well.

Took the car for a drive, and didn't notice any change in performance/economy. Unfortunately, I couldn't hear if I've cured the hissing as there was surface water on the road, which made a very similar noise to the hissing.

Will update on the next dry day.

 

[Smartbear]

Check the ccv hoses as well, not good to have a lot of oil in the inlet manifold-could be a sign of a bad ccv?
Rob

 

[David]

Check the ccv hoses as well, not good to have a lot of oil in the inlet manifold-could be a sign of a bad ccv?
Rob

Thanks, I will have a look!

 

[David]

Update: (or lack of...)

Hissing noise still present.
Petrol smell still present.

Injectors removed and cleaned today.

INPA didn't throw up any error codes, nor did it display any worrying stats or short/long term fuel trim percentages. So it doesn't look like I've got any unmetered air getting in?

Next up:

- Check fuel lines and pressure
- Check CVV

 

[Marlon]

Its a new one on me David :?
Hope you get to the bottom of it

 

[goldbcfc]

when was the fuel pump last changed?

 

[David]

when was the fuel pump last changed?

Not aware of it ever being changed, but will double check the history that came with it. I've owned the car just over a year now, and it's now done 35k miles.

 

[ph001]

Hate it when people leave threads open and don't feed back to the community. I wonder if David ever got to the bottom of this?

 

[David]

Hate it when people leave threads open and don't feed back to the community. I wonder if David ever got to the bottom of this?

Thanks for the valuable input and constructive comment! :x

I've made no progress with this since, other than removing my AFE CAI, and fuel consumption has improved slightly.

 

[Carmad84]

I have the same sound on very light acceleration but no petrol smell.

I just thought as the tech guy that it was a common thing.

I think you have to have good hearing as I keep trying to get other people to hear it and they never can, I think some think I've gone crazy!

 

[David]

I have the same sound on very light acceleration but no petrol smell.

I just thought as the tech guy that it was a common thing.

I think you have to have good hearing as I keep trying to get other people to hear it and they never can, I think some think I've gone crazy!

Yes, I’m the same. Drives me nuts but no one else seems to notice it. Seems so obvious and intrusive when driving past close walls/cars/railings as the sound bounces off them.

Still no progress unfortunately!

 

[Scooba_Steve]

The work involved getting the manifold off, if you're going to check the CCV, you might as well just replace it for what they cost.

 

[David]

The work involved getting the manifold off, if you're going to check the CCV, you might as well just replace it for what they cost.

Definitely agree with this. That's the next step, though I'm not sure when I've get a chance to do it.

David

 

[Scooba_Steve]

Probably the starter too :lol:

 

[David]

Finally getting on top of this. Pausing mid-work with research needed.

I’m replacing the CVV and very nearly have the manifold out.



The good(?) news is that the CVV is leaking, and looks like it has been for a little while, as you can see from the picture.

The problem I’m having now is that my manifold (early 3.0si has a line from the master cylinder running through it.



Does anyone have a link to a how to specifically for the Z4 early N52? Can only find other series...

 

[David]

A quick bit of research tells me it’s the “master brake booster vacuum hose” as desribed somewhere here:

http://www.zpost.com/forums/showthread.php?t=455180

Back to work...

 

[David]

And then out came the manifold.



On closer inspection it looked like the oil was coming from the secondary DISA, so I removed that and...



The seals are toast! Planned on scraping out the rubber, before realising that the inner rubber seal (for the flap) has had it as well.

Looks like I’m replacing this too. And this could very well be the cause of the hissing noise.

Also, there’s a bit more oil than I’m comfortable with inside the manifold, so looks like I am right to replace the CVV in the first place, but happy that I’ve found another potential culprit.

As a side note, I’m also replacing/refurbishing the starter motor. Will decide which one once it’s out.

 

[David]

I have the same sound on very light acceleration but no petrol smell.

I just thought as the tech guy that it was a common thing.

I think you have to have good hearing as I keep trying to get other people to hear it and they never can, I think some think I've gone crazy!

I’m happy to inform that both the hissing and performance issues have gone as a result of removing the mani and replacing the Secondary DISA and CVV. As you can see from the pictures I posted a few replies up, the hissing was most likely caused by the disintegrated DISA seal.

Case closed!