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March 2006 Willie's Workbench Engine Diagnostics

Posted in How To: Tech Qa on March 1, 2006
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A neighbor dropped by the other day for what I thought was a friendly chat. However, he didn't shut off his engine, and I couldn't help but notice by the sound that one or more cylinders weren't firing. Yep, sure enough he wanted to know if I could find out why his truck was lacking power. He said he'd done a "tune-up" that included a new cap and rotor, spark plugs, and even new spark-plug wires, but it still didn't seem to be running right.

OK, I said, "pop the hood and I'll take a look" as I headed to the toolbox for my "gun." No, I didn't shoot his engine, as the gun I was using was my noncontact infrared thermometer. It kinda does look like a gun with its pistol shape, but more like Buck Rogers' ray gun. From about a foot away, I aimed the gun along the exhaust manifold, transversing its length a couple of times, and it indicated that the No. 2 hole was about 100 degrees lower than the other holes. Because of the new wires, cap, and plugs, I pretty much ruled out an ignition problem. The problem turned out to be a bad electrical connector on the injector.

But back to the gun: What it does is measure "surface emissivity" of an object with an infrared light sensor. OK, it simply measures how hot an object is without physically touching the object. The "field of vision," or how much area the gun reads, is determined by the distance from an object. For instance, my Raytec Raynger ST will measure a 1.5-inch area at one foot, but at 5 feet the area expands to about 5 inches. It has a temperature range from -25 to 750 degrees Fahrenheit as well as its counterpoint in Celsius. To promote proper aiming, a laser pointer is incorporated into the gun so you can be right on target. One thing that I did find is that it doesn't like shiny surfaces such as aluminum or chrome thermostat housings. The solution is to just put on a few strips of black electrical tape or even masking tape on the object.

What else is it useful for? Well, beyond the introductory example with the exhaust manifold, I've used it for numerous things. Take troubleshooting a cooling system. You can tell exactly at what temperature a thermostat opens by pointing the gun at the housing and letting the engine come up to temperature. There will be a major increase in temperature on the outlet side when it opens. No change means it is stuck open or closed, depending on the overall temperature. Run it across the face of the radiator to check for plugged tubes or to measure how different fans and shrouds affect the overall cooling ability of the radiator. Use it to check heater or air-conditioner temperature at the outlets.

Want to check if your catalytic converter is operating properly? The older converters will show 100 degrees F (or more) between in and out exhaust temperature readings, while the newer three-way converters maybe show only 20 degrees. But there always should be a difference. However, if the output is in the 100-degree area or so, then you've not got a converter problem but a bunch of fuel leaking into the exhaust system from a non-firing cylinder, a bad injector, or a leaking exhaust valve.

Got a noise that sounds like a bad wheel bearing? Or is it the pinion bearing? Most likely, the noisy one is going to make more heat, so use the gun to determine which one it is by the rise in temperature.

If you're like me, you'll find endless uses for your gun including a few playful ones.

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