[AD18]

Hi All,

I posted this question in the UK forum but things seem pretty quiet there now, so thought I'd try here.

Has anyone with a 335i experienced their turbo 'hissing / psss' sounds have stopped?
Where previously I could get sounds from building some boost and letting off, I can no longer get any no matter what. I'd like to investigate why this has happened as I feel there are some knock on effects, but not sure how or what to look into.

Symptoms:
- Turbo sounds have gone
- Car feels slower in the lower rpm ranges, as if I need more throttle to do simple overtakes on the motorway.
- At higher rpms car pulls strong, but this gives the feeling of a heavily turbocharged car where its slow at low rpm and then fast at higher. (Thought the car felt faster than this but maybe I'm just used to it now?)
- Lumpy engine running at idle

I thought either:
- Diverter valve (/BOV?) is passing / not sealing properly
- Small leaks from some hoses
- Perhaps starting to experience issues with the turbo itself.

Car is all stock and now on 100k miles, no error codes.

I don't have the equipment but I thought if there was a way of measuring turbo boost pressure then that might reveal something?

Any advice or avenues to explore will be helpful

Thanks

[TheGoodTheBadTheUgly]

Hello, might be something super simple as a boost leak because of loose components and on the extreme end, whicj is more unlikely, could be issues with the turbo itself.

You are right that measuring the built boost would be the best way to diagnose what is going on.

The N55 is equiped with a TMAP sensor (temperature-manifold absolute pressure) on the chargepipe before the intake manifold and by reading its output values compared to what is requested by the car's ECU, we can learn more about potential boost leaks. We can also look at wastegate duty cycles if we must go further.

I recommend getting a proper scanning and logging tool for this car. You can learn a lot from it, diagnose multiple things and prevent larger issues from happening.

Getting the MHD N55e monitor pack with a MHD OBDII device would be good.

You could also see if Torque App and a regular bluetooth adapter could work.

Meanwhile, have you checked to make sure that you have no obvious hardware issue? Is the chargepipe showing cracking (this is a well documented issue that has arised multiple times even on non tuned/stock cars)? Are all the pressure pipes still well connectes to each other as wrll as the intercooler?

[AD18]

Originally Posted by TheGoodTheBadTheUgly

Hello, might be something super simple as a boost leak because of loose components and on the extreme end, whicj is more unlikely, could be issues with the turbo itself.

You are right that measuring the built boost would be the best way to diagnose what is going on.

The N55 is equiped with a TMAP sensor (temperature-manifold absolute pressure) on the chargepipe before the intake manifold and by reading its output values compared to what is requested by the car's ECU, we can learn more about potential boost leaks. We can also look at wastegate duty cycles if we must go further.

I recommend getting a proper scanning and logging tool for this car. You can learn a lot from it, diagnose multiple things and prevent larger issues from happening.

Getting the MHD N55e monitor pack with a MHD OBDII device would be good.

You could also see if Torque App and a regular bluetooth adapter could work.

Meanwhile, have you checked to make sure that you have no obvious hardware issue? Is the chargepipe showing cracking (this is a well documented issue that has arised multiple times even on non tuned/stock cars)? Are all the pressure pipes still well connectes to each other as wrll as the intercooler?

Hi there! Thanks for the reply, some good points there!

I'll look into those MHD applications, I couldn't find out what I needed to measure things like boost so that gives me a good starting point. Is it future proof in that I could use it for future cars or is it specific to only the N55 as the name suggests?
Any idea what a shop that does turbo diagnostics would be using as they'd need to test any and every vehicle?

I'm wondering whether there is something hardware related that has ever so slightly failed, especially with the long periods it was sat stationary during covid, something must have dried out and perished.
I'll need to see if I can spot anything from a simple engine bay view. Unfortunately, I don't have any lifts or fancy equipment so I am quite limited currently with what I can do and probably why I feel stuck with this issue. Things like checking intercooler pipes might be tricky for me if its hidden behind the front bumper. Shall check the chargepipe though that should be easy, good point!
Will see how I get on, thanks!

[TheGoodTheBadTheUgly]

Originally Posted by AD18

Hi there! Thanks for the reply, some good points there!

I'll look into those MHD applications, I couldn't find out what I needed to measure things like boost so that gives me a good starting point. Is it future proof in that I could use it for future cars or is it specific to only the N55 as the name suggests?
Any idea what a shop that does turbo diagnostics would be using as they'd need to test any and every vehicle?

I'm wondering whether there is something hardware related that has ever so slightly failed, especially with the long periods it was sat stationary during covid, something must have dried out and perished.
I'll need to see if I can spot anything from a simple engine bay view. Unfortunately, I don't have any lifts or fancy equipment so I am quite limited currently with what I can do and probably why I feel stuck with this issue. Things like checking intercooler pipes might be tricky for me if its hidden behind the front bumper. Shall check the chargepipe though that should be easy, good point!
Will see how I get on, thanks!

You are right in the sense that the MHD package you buy is specific to that platform. Hence if you buy the N55e series monitoring package, you will only be able to use it on N55e. For the hardware though, you can get an adapter that would work on other cars.

I have no clue what a professional shop would do, but here is a logical workflow that I think might be part of some of their steps:
- Scan for obvious code
- Monitor car boost, wastegate duty cycle and other relevant parameters
- If boost target is not met (underboost), check for piping connections
- Inspect wastegate and ensure it is in working conditions (mine was completely rusted through and would not build boost at some point)
- If no obvious leak is found, conduct a smoke test to find anything obvious
- Remove and inspect diverter valve for teared diaphragm

Hardware that could fail:
- Charge pipes, intercooler joints
- Wastegate actuator. Actuation can be tested by applying vacuum
- Boost solenoids
- Diverter valve. DV failure can cause over or underboosting depending on how the part failed. If its overboost, you will have a compressor surge which you can identify by a chirping sound when revving