I'm not much of an mechanic but I was able to do a compression test on my 240D. Here are the steps I took;
1)Remove the metal fuel injector lines coming from the injection pump
2)Remove the return fuel lines, those are the braided lines that connect to each injector
3)To crank the engine, I bought a remote starter, which a tool that connects one wire to the negative battery terminal and the other side to the starter solenoid. Real easy to connect. I bought it from autozone for $15 and it allowed me to crank the engine from the engine bay with the key in the ignition all the way to the right. Pretty cool tool. Otherwise, you can have someone crank the engine for you.
4)I bought a diesel compression tester from Ebay for about $40 shipped.
5)At this time, you can remove the injectors one by one and test them. Only have the injector that you are testing out of the engine. Under the injector, you will find a heat shield. It's a metal gasket looking piece. That needs to be replaced with a new one when you reinstall the injector.
6)With the injector out, plug in your compression tester with the injector adapter and tighten.
7) Crank the engine or use the remote starter to get a reading. About 6 to 8 cranks should give you the compression reading. I rested the compression tester, cranked the engine with the remote starter in one hand and the other hand pushing the "stop engine" lever so that the engine doesn't start.
8)Now you should have a reading!
9)Unplug the compression tester and reinstall the injector with a NEW heat shield. Make sure the heat shield is facing the right direction. Just make a note to see what direction the original heat shield was before you removed it.
10)Now, to the next injector and so on.
11)When all done, you should reinstall the metal injector lines that connect one end to each injector and the other to the injection pump. You should also replace the braided return lines(those are the plastic lines you removed) with new ones. They sometimes leak when reinstalled. Plus they are pretty cheap to replace. You can buy the line for all the injectors for probably $8.
12)Leave the connection coming from the metal injector lines to the injector loose. Now with everything tight except those five connections, crank the engine until all five of them are leaking out a little fuel. Once that happens, tighten those connections and the engine should be back to normal.
-A couple notes. Some people suggest you test compression on a warm engine, others say a cold engine. Others suggest if you get a low reading (probably under 290), you should squirt a bit of engine oil in the injector hole and then test the compression again. If you get a low reading, then you probably have bad or worn rings.
-Badly adjusted valves will also give erratic readings.
-You need to buy heat shields for each cylinder, new injector return line, a compression tester. A breaker bar helps free the injector from the engine. Not sure what the size the fittings on the metal injector lines are.
Hope that helps!
