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

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:

View: 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.

@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]

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.

 

[NZ00Z3]

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

Hi David

It can be very hard to find the cause. Don't go throwing parts at the car without having done some very good diagnosis first.

How to track it down:

1. Download the engine codes and look for lean engine codes or anything else out of the ordinary.
   
   
2. Remove the "beauty covers" off the engine so you can see what's going on with the injector rail etc. Do a good "look, watch and listen" while someone starts the engine and runs it up the rev's to where the hiss can normally be heard. Look for fuel leaks and try to pin point where the hiss is coming from.
   
   
3. Get a scanner that will monitor the live fuel trims .
4. With the engine running (with the hiss happening if possible), while watching the fuel trims, squirt some carb or brake cleaner at the area to be tested for the leak. The fuel trims should jump when the engine sucks in the cleaner. The engine may not change tone but the DME will be quick enough to pick it up and change the fuel trims.

Going by your symptoms, here are my guesses (sitting in an armchair 10,000 miles away and they are likely to be wrong) and reasons why.

1. You have a leaking inlet manifold gasket.
2. An injector fuel rail or O ring is leaking

Reasons:

• To get a smell of fuel on start-up you either need a fuel leak (Injector O Ring or rail) or your DME sees the mixture as lean and is dumping lots of fuel into the system
  
  
• Inlet manifolds have a vacuum on them. For you to get the fuel smell on start up, the leak needs to be near the injectors or at the injectors
  
  
• The noise gets worst on light acceleration. The manifold vacuum changed as you put your foot down. Highest vacuum with throttle closed, lowest vacuum with throttle fully open. At idle the volume of air going through the leak is enough to lean out the mixture but not enough to cause a hiss. As the engine rev's up it needs more air and the air volume increases through the leak and causes the hiss. There will be a balance point between manifold vacuum and air volume through the leak where the amount of air coming through the leak will either reduce and the hiss will stop or it will open up the hole and the hiss frequency will change and the noise will be perceived to have stopped.

Its a bit long winded, but I hope it will help you.

Regards

Muzz

 

[t-tony]

I get a bit of a whistle at light throttle openings since I fitted my induction kit which can be a little annoying but that's all.

Tony.

 

[NZ00Z3]

Hi David

Just been reading a E46 forum and came across a couple of comments about how a damaged diaphragm in the CCV separator can cause a whistling. Probably a likely source for your problem.

Regards

Murray

 

[David]

Hi David

Just been reading a E46 forum and came across a couple of comments about how a damaged diaphragm in the CCV separator can cause a whistling. Probably a likely source for your problem.

Regards

Murray

Thanks Murray,

My INPA software and cable arrived today, so I will try hook it up over the weekend and see if anything unusual shows up.

One thing I have noticed this week is, although the MPG has dropped (4mpg down on my commute, and nothing has changed) and I've still got an apparent air/vacuum leak, the idle is bang on, and the needle barely quivers.

I would've expected any unmetered air getting in to cause a lumpy idle?

 

[NZ00Z3]

Lumpy idle occurs when the engine is cold and in open loop mixture control. Once the engine gets warm, it switches to closed loop mixture control and the DME will get a lean signal from the O2 sensors and compensate for un-metered air/lean mixture by dumping in more fuel. That's why you look at the fuel trims to see whats happening.

Good luck with your investigation.

 

[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

 

[billz]

A strange one David. Hopefully it is not too big an issue. Trouble is its the small issues that sometimes take the longest time to find

 

[billz]

I meant to ask did you manage to locate some wheel decals ?

 

[David]

A strange one David. Hopefully it is not too big an issue. Trouble is its the small issues that sometimes take the longest time to find

Just going through it all systematically Bill. The positive is that it's a good learning experience. I know a lot more about the engine than before I started this journey!

I meant to ask did you manage to locate some wheel decals ?

Completely forgot about that! Will probably save it for a rainy day. Currently desiring a set of 224s or ACS wheels though.

 

[Antm72]

Hopefully you will find this i can imagine it to be annoying it would be too me.
Good luck in finding this

 

[David]

Hopefully you will find this i can imagine it to be annoying it would be too me.
Good luck in finding this

Thanks Ant,

It is annoying! More so that I can't replicate the noise when the car is not being driven, which makes searching for it a right būgger.

Thought I had a breakthrough last night in that it can be heard from the passenger side, and that's where the fuel filter is on most BMWs.

I got all excited, started googling for a replacement on mine, to find that it's a lifetime part, and is positioned in the fuel tank. At least I can cross that off too!

 

[Antm72]

Its not a belt noise is it ? High pitch tensioner whistle ?
Doesn't explain the smell but maybe the noise under load ?

 

[David]

Its not a belt noise is it ? High pitch tensioner whistle ?
Doesn't explain the smell but maybe the noise under load ?

It's not a whistle. The only noise I can compare it to for reference is the squirting noise a water pistol makes.
This happens at around 2500rpm, and is heard coming from the passenger side of the car.

 

[t-tony]

Did you have this noise with the original airbox fitted David?

Tony.

 

[Redline]

Also check the oil filter. Sounds odd but I had a filter collapse. It created a whining hissing noise as oil was pushed through what was left of the filter or the by-pass valve. Highly unlikely to be this to be fair but you know.

 

[Brian4]

Also check the oil filter. Sounds odd but I had a filter collapse. It created a whining hissing noise as oil was pushed through what was left of the filter or the by-pass valve. Highly unlikely to be this to be fair but you know.

Ian makes a good point regarding the noise, probably doesn't explain the fuel smell. The engine in the 3.0is is the N52 which doesn't rely on vacuum in the inlet manifold and throttle body to control engine speed but the valvetronic system controls engine speed with the throttle being fully open once the engine has started and a separate vacuum pump for servo etc.

 

[billz]

Just going through it all systematically Bill. The positive is that it's a good learning experience. I know a lot more about the engine than before I started this journey!

Completely forgot about that! Will probably save it for a rainy day. Currently desiring a set of 224s or ACS wheels though.

Would love a set of ACS Wheels.