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Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 23444
Experience:  BEng hons Mech engineering, in auto industry 22 years
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2004 BMW E46 320d saloon: I have had an ongoing issue which

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2004 BMW E46 320d saloon : I have had an ongoing issue which I believe to be either an intercooler hose leak / turbo leak. I am no expert but I know some of the basics i guess. Current symptoms include ;
- black smoke from exhaust especially under heavy acceleration (I'm guessing it's running rich due to a lack of air within the air/fuel mix)
- a struggle to output the same performance as it once did especially as it judders heavily around the 2K RPM mark which makes driving quite unpredictable & unpleasant.
- previous check up at an independent BMW garage noted a "possible turbo leak" on my paperwork.
- engine light is constantly on because of the ongoing issue.I replaced the MAF sensor last year but it didn't improve anything. I haven't been driving the car for the last year due to not needing it (I walk to university as a student) and therefore haven't followed up the issue yet. I am planning on using the car in a few months time and would like to sort it out either by taking it to a professional or by doing it myself (I like to learn as much as possible). Based off the information I've given you, I'd like to know what your best guess would be in terms of the culprit and if possible the best way to proceed in order to fix this problem. What tests should I perform if need be etc? I'm hoping it is simply an intercooler hose leak as opposed to a damaged turbocharger for obvious reasons.Cheers

Hello and welcome to Just Answer

I'd first check all the high pressure hoses post turbo/s for any split hoses or cracked metal pipes, also check the ends of the intercooler as its not unheard of to pop the end caps off under high boost.

If this is OK then check the small vacuum lines to the turbo and its connected control solenoid on the bulkhead, any cracks or leaks can give turbo issues
Also have a feel around with your bare hands with the engine running to see if you can feel any escaping gas under your touch. Another method is to use a soap and water solution sprayed onto any suspect areas - if there's a leak it'll bubble up with the engine running

Also check that the vacuum hose running to the dump /or turbo bypass valve is intact with no leaks as if the dump valve is opening prematurely you'll be losing all your boost

If this is OK then remove the high pressure intake hose after the turbo and have a feel of the turbine wheel - there should be no play radially at all - but a little bit of axial / end to end float is normal

one other possibility is that the wastegate actuator spring has gone soft so allowing the wastegate to open prematurely - if your actuator has a threaded end you can increase the preload on it to see if this improves things otherwise these units are quite cheap compared to a new turbo so it may be worth trying a replacement

The dump valve is on the turbo boost air (post compressor) side its there to blow off or 'dump' the excess boost pressure you get when you close the throttle ( like just before a gear change)
the important thing with a dump valve is that it seals properly when its not being operated if the valve has a torn seal or a broken spring then it'll blow off before it should and you'll lose boost pressure

this video shows how you can test it

as for the wastegate then this is on the exhaust side and 1st thing to check is if the wastegate 'penny' or flap can be fully seated
if you remove the wastegate actuator and then look inside the turbo exit you'll see the wastegate penny moving back and forth as you move its arm if you smear a little grease or engineers blue onto the face of the penny and snap it shut and reopen it you shoudl hopefully see the seal line all around the penny

if thats OK you can then test the wastegate actuator with compressed air to check its opening up this shows if its going to be able to control boost
this video shows how ( from about 2 mins in)

and to check the spring ( is it blowing off too early) you need a spring balance or some other method of measuring the spring force as shown in the previous video

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
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Thanks Matt

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Customer: replied 5 months ago.
incredibly in depth response. I now have a lot of testing to do when I get the chance. Thank you very much for sharing your knowledge.