The other day my wife was driving my Mercedes on the expressway when it suddenly lost power in the high speed lane. She proceeded to move over to the right lane and by the time she got there it quit altogether. Repeated attempts to start it failed, and we towed it home.

When I got it home, I couldn't get the engine to turn over. As I had been having some trouble with the battery, I immediately replaced it with a new one. Unfortunately, that didn't fix the problem although the engine will now turn over when I hit the starter - although, sometimes, it seems reluctant. When the engine turns over, I can hear a squeak (just a single squeak) after every third or fourth revolution. The squeak seems to come from the bottom of the engine.

The question is how to diagnose the problem. Can you give me any ideas about where to start? The car is a 1981 Mercedes 300 D(iesel). It has about 215,000 miles. To date it has given excellent service and I have had no major problems, the only thing I've ever had to replace other than wear components (brakes, etc.) is the alternator. Except for the squeak, I'd suspect the high pressure fuel pump. Is there a recommended way to check that out? I'd appreciate any help you could give on this.