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      06-26-2015, 10:26 PM   #1
loesch
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DIY: Locating boost leaks in N55

First, I do not claim to be an expert by any means. This is just an account based on my experience.

So how did I come to the conclusion that I have a boost leak? The first thing that I noticed was that I was not hitting targets, especially at higher RPMs. I saw some other people with logs showing 17psi at 6,000rpms so I figured something wasn't right. Also, PWM spikes almost immediately to 99. This shouldn't happen at lower RPMs like this.


Newguy123 was a big help as he pointed me to the company that puts together a tester that works perfectly for the N55. http://turboboostleaktesters.com/n55-engine-all-models/. It's a very nicely put together tool. Just make sure they send 2 clamps with it. Mine first showed up with just the one so I couldn't attach it to the inlet tube. They were great about it and sent another one to me right away though.

This tester is a must for us. Pure has said that 90% of the cars they get in their shop have some sort of leak. That says it all.

Starting the test

First, Remove the under body plastics so you can get a friend to help find leaks while you have the system under pressure. This is super easy and just requires the removal of several bolts.

1, Unclip the intake from the airbox. If you have the stock intake then unclip the top part of the airbox. You might be able to get away with leaving it but I would just remove the clips to make things less prone to breaking.
2, Loosen the flat head screw on the worm clamp shown in the image below. Squeeze and pull the intake free
3, 4, Remove the 2 screws that hold in the EGR fitting. Carefully pull it straight up and out.
5, Remove the 10mm bolt that secures the intake tube.

Now remove the intake tube.


Now you have access to the mounting point for the boost leak tester shown below.


Remove the rubber gasket from the turbo inlet tube. In this instance I have the Pure inlet tube but it should be the same procedure for the stock inlet tube.


Pre-tighten the bottom clamp on the boost leak tester until it won't fall off. Align it as shown in the pictures below...




Now seat the tester onto the flange of the turbo inlet tube and tighten the clamp to secure it.


Get out your air compressor fill to about 25psi. You don't want too much because you want to add pressure to the system gradually. Attach the air hose. You will use a standard tire inflator tool. Now REMOVE THE OIL CAP!! This helps to let the crankcase pressure escape to save your seals. Slowly add air until the tester gauge reads about 3 - 5 psi. At this point you may already find your leak. You'll hear air hissing and can feel around and listen to see where it's coming from. As you fix your leak(s), keep increasing the pressure slowly until about 20psi on the tester. In my case the air was escaping from the hot side charge pipe at only about 4psi. I had thought it was goodentight but apparently not.


While I was in there I also decided to empty my catch can. Always a good idea to do that every once in a while. I had a good bit of watery grossness to dispose of.
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      06-26-2015, 10:35 PM   #2
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Reserved for results once leaks are all gone and the car is logged.
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      08-03-2015, 10:10 PM   #3
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Any updates on this?
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      08-09-2015, 12:28 PM   #4
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Sorry. Not really. Funny thing is that my logs look almost exactly the same after fixing this leak. I'm not sure if another leak occurred or what.
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      05-23-2016, 03:43 PM   #5
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Quick question. What's the diameter size of the pipe where you put on the Boost leak tester? Or even better, what's the diameter of your boost leak tester on both sides? I want to make my own since I live in Mexico and the site charges me 50 USD for just shipping that thing.
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      06-05-2016, 09:37 PM   #6
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3"
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      06-19-2016, 09:33 PM   #7
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Hi Loesch

Are you still a few psi short up top - like me? I have been trying to trouble shoot a dozen times over the last 6months, but no success so far.

I am comparing my lack of boost to this log from Peter...I am starting to think that his log was just run in at colder temperatures - hence the turbo can make more boost. The F-series turbo inlet is different so I deviced a leak tester myself from a plumbing cap
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      06-19-2016, 09:54 PM   #8
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Quote:
Originally Posted by harkes View Post
Hi Loesch

Are you still a few psi short up top - like me? I have been trying to trouble shoot a dozen times over the last 6months, but no success so far.

I am comparing my lack of boost to this log from Peter...I am starting to think that his log was just run in at colder temperatures - hence the turbo can make more boost. The F-series turbo inlet is different so I deviced a leak tester myself from a plumbing cap
I went Stage 2 so definitely no shortage up top now.

Your log looks pretty much the same as mine on the stage 1 at its best.
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      06-19-2016, 11:44 PM   #9
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Quote:
Originally Posted by loesch View Post
I went Stage 2 so definitely no shortage up top now.

Your log looks pretty much the same as mine on the stage 1 at its best.
Haha - that is also a way to fix it

God knows I would love a Stg2, just cannot justify it for city driving with 2x 200usd shipping and 30% import tax so just want to get the most from the stg1.
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      09-09-2016, 05:35 PM   #10
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Hey Loesch,

Running the test on an identical PS2 turbo, intake, etc. I disconnect my oil catch can and I can hear air hissing from the oil cap removal and the line going to BMS OCC at around 7-12psi. Is this normal?
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      08-18-2019, 09:39 PM   #11
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Doing this procedure. The turbo inlet seal starts leaking at 5 psi. Any way to seal that better? It isn't designed to see pressure.
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      06-30-2020, 11:07 AM   #12
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curious why didnt you do a smoke test? why go throught the hasstle of pressurizing the system like this way? wouldnt the smoke test do the same and give you a visual of leak better than listning to hissing sound?
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      08-19-2021, 08:07 PM   #13
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Hey just curious did you ever find the boost leak on your N55, ive fixed all my leaks new DV and my tuner says i still have a leak somewhere
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      09-22-2021, 05:02 PM   #14
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Same here

I have the exact same issue on M135i, same engine except it has an electronic wastegate. Logging 2-3psi below target on MHD stage 1. MHD say it looks like a boost leak, but three different workshops have had it and all say no leak. Changed the diverter valve, checked the PCV.
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      05-14-2022, 10:11 PM   #15
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Bringing this back to life...

I recently started hearing more noise on hard acceleration. I logged a few runs and saw my pressure still strong but not at where id expect it. I have the Dinan Stage 2 tune for what its worth. Not sure what the PSI is supposed to be on that tune, and may just call the guys at Dinan and ask.

The noise made me think I might have a boost leak, and I went ahead and purchased the tester from this thread. I too had the same issue that the turbo inlet pipe couldn't hold pressure above 5 PSI. I do think the noise could be related to the vacuum leak on the inlet pipe, So I decided to order the VSRF inlet pipe, and I checked all the other connections in the charge pipe etc and they seem to be good.

I might try and fit the tester on the inlet side of the intercooler, and see if I can spot any leaks from that point on. I do wonder about the O rings in the intake manifold, and perhaps that could be a sneaky location for some leaks.


I also plan to buy complete aluminum intake charge system - from turbo outlet to intercooler, lower charge and upper charge. I am running a Wagner EVO I btw.
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      01-22-2023, 10:55 AM   #16
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what is the leak sound like at high RPM? mine is squealing like a loose belt(all new tensioner, belt etc.) beyond 1/2 throttle. have driven much because of a Valve cover oil leak that hopefully I'll fixed soon. any insight will be helpful.
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      04-12-2023, 04:50 PM   #17
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Quote:
Originally Posted by AndyW View Post
Doing this procedure. The turbo inlet seal starts leaking at 5 psi. Any way to seal that better? It isn't designed to see pressure.
I'm running into the same problem, turbo inlet seal breaks loose at 5psi during the test. I thought it might be the Diverter Valve, so I upgraded to the GFB DV+, but still have the same problem. Anyone successfully run this test at the turbo inlet pipe, or find a solution to the leaking of it?
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