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

WHICH IS BETTER FOR DETERMINING PROBLEMS WITH ENGINE COMPRESSION PROBLEMS, A COMPRESSION TESTER OR CYLINDER-LEAKAGE TESTER?

Both have their place. To best pinpoint compression problems, these testers work hand-in-hand. Generally speaking, a compression tester is your best bet to determine which cylinder has compression loss. A cylinder-leakage tester helps you determine the source of leakage from a cylinder with low compression readings.

WHEN TESTING CYLINDER LEAKAGE, HOW MUCH IS TOO MUCH?

Manufacturers don’t provide specifications for cylinder leakage, but most engines in good mechanical condition reveal less than 20-percent leakage (some engines can reveal cylinder leakage readings as high 30 percent and still perform OK). As a general rule, leakage of more than 20 percent indicates a problem with the cylinder.

When there is excessive leakage, remember these potential sources:

Air escaping into the crankcase indicates blow-by due to worn rings, a worn or damaged cylinder, or a cracked or burned piston.
Air escaping into the radiator indicates a compression leak into the cooling system through a bad head gasket or a crack in the head or cylinder.
Air escaping into the intake manifold tells you there’s a leaky intake valve.
Air escaping out the tailpipe indicates a leaky exhaust valve.

SINCE I DON’T DO THAT MUCH ENGINE WORK, IS A BORESCOPE A WORTHY INVESTMENT?

Borescopes are often perceived only as tools for inspecting engine wear and damage, but they can do so much more. For instance, you can look inside hidden areas for fluid leaks, check for gear wear inside differentials, inspect HVAC system airflow control doors, find serial numbers and production dates/codes in concealed areas, and inspect mechanisms in tight spaces like window tracks and regulators. Since you can make these inspections without disassembly, it can make your diagnosis more efficient using a lot less labor. To put this into context, just think of the times where you disassembled something for inspection reasons only to find nothing wrong.

WHAT FEATURES SHOULD I CONSIDER WHEN SHOPPING FOR A BORESCOPE?

Features directly relate to the applications where you plan to use the borescope. Traditionally, rigid borescopes use a straight inspection tube using lenses to create and transmit the image. Flexible borescopes, on the other hand, often use fiber-optic technology to carry the image for viewing. The latest models now feature electronic imaging technology where you can view inspections on an LED/LCD video screen. In some cases you can also project the image on a larger computer screen and even save videos of your borescope inspections. This can come in handy for building diagnostic files or even to show to your customers.

You will also want to consider the thickness of the inspection tube that the borescope uses to make sure it’s both small enough and flexible enough for small openings. Some borescope models also offer articulation control so you can control your point of view when making an inspection. Also consider special attachments such as mirrors and other implements that may help with inspecting certain components, such as engine valves.

To see if a given borescope is the right one for you, see if your equipment rep will let you try one out for a short period before making a purchase commitment. If possible, try several different models out first to make sure you’re purchasing with confidence. If you can, also get the opinions of other techs on their experiences with a borescope.

IS A VACUUM GAUGE STILL USEFUL FOR DIAGNOSING PROBLEMS WITH TODAY’S ENGINES?

Although it’s been around for many years, a simple vacuum gauge connected to the intake manifold provides valuable diagnostic information about an engine’s ability to move air in and out of its cylinders. After all, an engine is really an air pump of sorts and without being able to both take in and exhaust air consistently, it’s impossible to achieve good engine performance. You can also use a vacuum gauge to check for vacuum at vacuum-operated accessories like HVAC controls and solenoid valves.

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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