Mercedes Benz BlueTec Vacuum Pump Rattle
Vehicle: 2014 ML350 Bluetec.
Symptoms: Rattle, knocking or tapping sound coming from passenger side of engine. In this case rattle or tapping is noticeable only after vehicle is warmed up and does not follow engine rpm. Noise will disappear when engine is reved up at idle or while driving, it is noticeable only on idling. Do not mistake it with an engine bad bearing or timing chain issues.
Problem: Issue is vacuum pump located on front of engine on passenger side. Pump will cause knocking or tapping sound which can easily mistaken for a timing chain rattle or other internal engine problems, bearings, lifters, etc. Mercedes Benz ML350 vacuum pump cost about $500 for a decent quality (Hella) and $150 or so if you want to take your chances with Amazon parts/quality.
Repair: Remove and replace vacuum pump. Time to replace is about an hour at most, difficultly is minimal and can be done as a DIY with few tools. Tools: 3/8 ratchet and extension, E10 torx socket (all bolts are E-Torx E10), pliers and flat screwdriver.
Removal and installation: Remove engine cover and engine inlet air hose. No screws on both, pull engine cover upwards to remove, same goes for inlet air hose. Remove vacuum air box located in front of vacuum pump, two E10 bolts. remove bolts and then pull vacuum box upwards to release and remove.
Next remove vacuum pump line, press on both tabs simultaneously while pulling on it.
Remove harness bracket and unclip harness, has two clips. Vacuum pumps has four E10 bolts, remove bolts and pull vacuum pump out. below shows positioning of vacuum pump bolts.
Old vacuum pump pulled out of engine.
Installation: Installation is pretty much reversal of removal, clean thoroughly before installing new pump to avoid any leaks.
One thing to note on installation, make sure to align slot on engine with water pump axle when installing new pump, image below.
Do not overtighten vacuum pump bolts, aluminum doesn’t take much to break, just tight enough.
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