Tool Q&A: Make engine diagnosis easier with the right tools

Technical Editor Dave Cappert answers your questions about borescopes and more.


WHAT SORTS OF READINGS SHOULD I NORMALLY EXPECT FROM A VACUUM GAUGE?

Typically, with the engine at idle, you can expect a vacuum reading in the range of 15” Hg to 22” Hg. Of course, engine size, age, altitude and a number of other factors will affect this reading, so keep that in mind. You can also perform a cranking vacuum test, which may come in handy when you have an engine that won’t start, but you need to quickly check vacuum. When cranking, you should see a reading in the range of 3” Hg to 15” Hg.

WHAT TYPES OF PROBLEMS CAN VACUUM READINGS REVEAL?

The readings from a vacuum gauge can reveal an engine that’s mechanically out of time, improper valve sealing, intake system leaks, a malfunctioning PCV system, and a restricted exhaust.

HAS TECHNOLOGY BROUGHT ANYTHING NEW TO THE ARENA OF VACUUM GAUGE TESTING?

Yes, vacuum waveform diagnosis has become a widely accepted, advanced diagnostic technique used by technicians looking for more insight into vacuum readings and how they relate to specific engine components. Usually coupled to a lab scope, a vacuum transducer senses vacuum pulses from the engine and then passes on a signal for display as a waveform. The waveform has specific pattern characteristics that can then be compared and analyzed with other engine events to make determinations about engine mechanical problems. For instance, a vacuum waveform can be used to trace an intake valve that is not sealing properly.

I find it difficult to locate vacuum leaks on many of today’s engines. The old technique of spraying carburetor cleaner or even propane near vacuum connections just isn’t reliable and it’s hard to see many connections nowadays. Is there a better way to find vacuum leaks?

One newer method involves using an electronic vacuum leak detector. This type of detector provides a set of high-frequency ears that translate the presence of a leak into a visual or audible alert, signifying a leak. It’s more reliable than the poke-and-hope methods of the past. Another high-tech way of finding vacuum leaks includes the use of a smoke machine. With it, you introduce artificial smoke into the intake manifold and you then watch potential leak spots for signs of smoke. Ultraviolet dye can also be added to the smoke to make leaks more evident when inspected with an ultraviolet light.

WHAT NEW TOOLS WILL HELP PINPOINT ENGINE NOISES EASIER?

Several manufacturers offer electronic stethoscopes that feature technology to best amplify the sound transmission of suspect engine components. These stethoscopes enhance sound transmission to help pinpoint key components and also help to filter out extraneous noise from other sources in the engine compartment.

TRACING OIL LEAKS FROM ENGINES CAN BE BOTH TRICKY AND MISLEADING. IS THERE A QUICK AND ACCURATE WAY TO FIND LEAKS?

Ultraviolet dyes, when added to the engine oil, can help reduce the amount of time it takes for you to find oil leaks. You simply use an ultraviolet light to look for the presence of dye from potential leak points on the engine. Since you’re more likely to find the true source of oil leaks this way, it’ll help reduce comebacks, too.


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