Homemade stethoscope with hard probe over tire in rusty engine b…

The easiest way to find a vacuum or exhaust leak is with a mechanic's stethoscope. Remove the hard probe (which is used for listening inside hard parts) and attach an extension if necessary. About 3' of common garden hose is almost as good as a real stethoscope. For internal component noise, many people use a long screwdriver with the tip pressed against the component & an ear sealed to the plastic handle.

An exhaust leak will sound like puffing or popping. If the tailpipe is blocked (as when stuffed with rags), it will become a hiss audible even WITHOUT the stethoscope, but ignore any leaks on the muffler or tailpipe - they're not relevant to driveability problems, and the muffler's weep holes should be tiny leaks. Exhaust leaks on the EGR system, 2ndry air system, or manifolds are VERY significant & dangerous. For better access to the manifolds, remove the wheel liner as this photo shows.

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Before madly ripping out all the emissions systems on your vehicle, read this article to learn how each one benefits the engine.

A vacuum leak is an obvious hiss on an idling engine's intake system, vacuum lines, or vacuum-operated components (including the HVAC vacuum system & brake booster which can be checked from inside the cab). The hiss near the throttle body may be the normal sound of the air rushing past the throttle plate, which is loud enough to pass through the solid metal.

5.0Ls & 5.8Ls are known to suck in the plenum gasket on the R side, creating a hard-to-find leak. They also use an odd T40 bolt in the center of the plenum, which can require grinding or a special long bit to remove/install.

Owner caption October 2013 · Photo 0 of 5000