I’ve spent a lot of time talking about the systems that manage the fuel delivery to your engine. We haven’t said anything about the mechanical integrity of your engine yet, and we should. All of the aforementioned systems don’t mean diddly if your engine has a mechanical problem. It’s been my experience that engine mechanical is often overlooked in diagnosis. It shouldn’t be. If your engine has a mechanical problem, no amount of parts or sensors you throw at it will cure it. It is the heart of the system, after all.
One of the most basic tests you can perform to assess an engine’s mechanical integrity is a compression test. This test measurers the engine’s ability to draw in and compress air. In truth, your engine is nothing more than an air compressor. If it can’t do that efficiently, it won’t run right, and fuel economy will suffer. Here’s a video on compression testing that can walk you through the process.
Compression testing gets you in the ballpark. To find out the source of a compression problem, you would then perform a leak down test. The leak down test will tell you almost exactly where the compression loss is occurring should you have compression loss. Yes, in fact I do have a video on leak down testing.