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A Dose of Digital: Part 2 - Diagnostic Tool Buyer's Guide - Page 1 of 4

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© 2011 by Hib Halverson
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This part of Corvette Action Center's series on servicing Corvette engine controls surveys a wide variety of tools DIYs might want for diagnostic work.

Test Light Low-Down

Around since the dawn of automotive electrical systems, continuity testers, circuit testers or test lights, check DC circuits. Most consist of a metal probe attached to a plastic tube containing a 12V light bulb. On the other end, is a wire ending in an alligator clip. Attach the clip to a grounded part of the vehicle or the negative battery post, then touch the probe to any part of the electrical system at battery voltage. If the bulb lights, the circuit is continuous from where you're probing, back to the battery's positive post.

There are many variations, such as: powered test lights, which test de-energized circuits, special test lights for engine controls circuits which operate at five volts and microprocessor-equipped, "smart" test lights which determine polarity, can test powered or unpowered circuits and adjust to different voltages.

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A 12v test light typical of what a service tech might have in his or her tool box, in this case the MD1138 from Matco Tools. Matco's design is typical of many basic test lights. Matco also makes a similar unit with a coiled cord.
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A Waekon AST Pistol Probe uses LEDs and an audio tone generator to indicate circuit condition. The AST has a "headlight" for use in dimly lit areas and its shape makes it easier to handle than a conventional test light.
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The ultimate test light may be the Waekon "AST Pistol Probe" (PN 76200). Made by a Cleveland, Ohio maker of automotive diagnostic equipment, Hickok, Inc., and sold through Amazon and other tool vendors, it suits a geeky gearhead's fancy, if anything because Waekon terms it an "automotive signal tester with logic". The AST is a standout for its ergonomics-the pistol shape fits in your hand better than does a probe-type test light. Another unique feature is it indicates with both LEDs and a tone. Finally, it has a little "headlight" for testing in dimly lit areas. It's designed mainly for testing engine controls components. With a single connection you can identify power-either 5, 6, 12 or 24 volt systems-and grounds. The AST also detects pulses from Hall Effect devices, variable reluctors and signals from MAF sensors.

Also in the test light family are "noid lights" which are available from GM's special tool source, SPX Kent-Moore, Matco Tools and a variety of other sources. "Noids" are used to verify the engine's injector drivers are switching to ground. Pull the plug off the injector, stick the noid in the injector connector and crank the engine. If the circuit is live, the noid will flash as the injector driver connects to ground.

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This noid light comes with Kent-Moore's "Fuel Injection Diagnostic Kit" which is discussed elsewhere in this article, however, they are available on a stand-alone basis from many sources.
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The EFI Quick probe is another of Waekon's handy "test guns". It senses the the injector's mechanical action providing proof of pintle movement.
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More expensive than a noid, but easier to use because you don't have to unplug injectors, a difficult or impossible task on some engines-L98s and LT5s for example-is another Waekon product, the "EFI Quick Probe" (PN 76462) sold by Matco Tools. Touch it to the injector and, if the injector is operating, the Quick Probe's LED blinks. The clever engineers at Hickok, designed the Quick Probe to work by sensing vibration from injector pintle action. It's better than a noid because it indicates pintle movement as well as confirming the electrical signal.

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