Mercedes MBE 900 Testing Injectors - Pusher School Bus

Mechanics Hub - December 20, 2013
Working On Non Emission Diesel Engines

This Mercedes model is a 2004 so there are no emission components. These models are very reliable and the only trouble we've had is the overflow valve located between #5 and #6 cylinder which regulates the return fuel back to the tank. If you experience a power problem the overflow valve may be at fault. The fuel pressure can be checked by removing the engine lifting bracket located on the driver side front part of the cylinder head. Remove the fuel pressure sensor and install a pressure gauge.

Mechanical Injection Compared To Electronic Fuel Injection Systems

Years ago during the mechanical injection (non electronic) age of diesel engines the common procedure was to crack the injection line one at a time to check for a miss. Today since injection is controlled electronically the software enables us to do a quick test of each injector simply by pushing a button provided by the software program.

Technical Information Is Essential

The only catch is you need to have a laptop on hand with the software loaded up. Your local dealer will have it available. We also have an online program offered by Detroit Diesel that supplies us with technical help with repairs. The repair section is called “Power Service Literature”. There you'll find all the specifications and diagrams for mechanical repairs on all Detroit Diesel engines.

Since the injectors are checked using individual cylinder torque readings I can tell which injector is not performing well. This is a nice no fuss method that makes it easy to troubleshoot for a faulty injector. Our local Detroit dealer who is extremely helpful advised us that the injector fuel line and cross tube be replaced as well. The information in the “Power Service Literature” is very detailed so this repair will be straight forward.

As I mentioned in the video I wasn't sure if we were going to replace the one bad injector or all of them. Since it's obvious #5 injector is at fault we are going to change that injector alone and monitor the engine performance during the road test and carry out another injector cut out test.