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Efficient Engine Mechanical Diagnostics by Matthew Shanahan
Engine mechanical issues are becoming more common in our repair bays today, and they can be difficult to diagnose. Engines are built with more valves, camshafts and complex variable valve timing systems. Guessing is not an option for these failures, if you are wrong it could mean a lot of expensive parts and many hours of lost labor. Shanahan explains the DSO techniques that allowed him to accurately diagnose a Ford in about 45 minutes, a lot quicker than tearing the engine down on a guess.
A 1998 Ford Expedition 4.6L needed to pass a state emission test to be renewed, no codes, none of the monitors were complete, a noticeable misfire at idle that got better RPM increased.
He used the Ford IDS Power Balance to quickly identify the misfiring cylinders. This test is now available on many aftermarket scan tools. (Fig. 1) including the Autel MaxiSys.
Time to tear apart the front of the engine, right? No says Shanhan, it is time to do more testing.
With a Pico, he tested relative compression with a high amp probe and performed in-cylinder analysis with a WPS pressure transducer.
To read the complete article and watch the video, visit http://technician.academy
