Like most diesel engines, this BMW N57 uses an EGR – exhaust gas recirculation. What that means its some of the hot exhaust gases that still have some unburned fuel and oxygen are siphoned off, cooled and sent back into the intake. That helps lower the intake air temperature and get more complete combustion. The problem though, is along with the cooled gas you also get sooty carbon that makes a huge mess of the intake and piping. Here’s where the EGR enters the intake manifold, and here’s inside the intake. Look how nasty it is in there. That’s around 80,000 miles worth of carbon build up and this isn’t even as bad as we’ve seen. This much carbon acts as a flow restriction and messes with the carefully designed air patterns manufacturers spend millions designing and is generally a bad thing to have built up like this, so it needs cleaning.
Now me and the car’s owner are fairly proficient at working on cars, but we are often defeated by what seem like relatively simple tasks. This is one of them. Here’s some entertainment for you in the form of us trying our hardest to get the intake off to clean it…
We eventually settled for just cleaning the worst of the deposits, right where the EGR enters the intake manifold. It’s relatively clean throughout the rest of the piping, and from what we could see further into the manifold, so for now cleaning this lot out will do. To recap how to get at this, you’ll want to remove the engine cover, then air filter, then air box. Then remove the strut brace on the right side, and intake pipe. Then disconnect the charge pipe by pushing it towards the rear of the car and lifting up on the locking clip, then it’ll just slide back and off. You might want to unplug the sensor on the side of the charge pipe too. Then unplug the throttle body/anti shudder valve, it’s on the bottom but fairly easy to get to. Then it’s just 3 5mm allen bolts and the valve comes off and you are there.
To clean it up, you’ll want a scraping tool and a lot of brake cleaner. Spraying it down, then wiping it out works well. Once you’ve scraped all you can, spray it down some more, and if you can use some kitchen roll to wipe the rest.
