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Basics of Troubleshooting


Learn what you need to have to have and how to diagnose a problem quickly and efficiently.
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The secret of effective diagnosis and troubleshooting is to have a logical, well-ordered system. Following a logical step-by-step procedure will get you to the root cause of a problem quickly and efficiently. Repair manuals will have a diagnostic tree that goes in a logical progression. It will ask a question, usually yes or no, and depending on the answer will branch off in two or more directions. The last box in the tree will have the problem and how to correct it. The example shown is a simple one. A more complicated system will have branches going into specific tests and then have 2 or more branches from there depending on test results.

You will need some basic test equipment to perform your diagnosis. A 12-volt test will tell you if a circuit has power or, when hooked up in reverse, will tell you if a ground circuit is good. A good volt-ohm-meter (VOM) will be needed to perform specific voltage and resistance tests. You can get a good meter at any Radio Shack or Best Buy store. A digital meter is an excellent choice because they are easier to read than an analog meter. I have both digital and analog meters in my toolbox because sometimes an analog meter is best for a certain job. Most VOM's have an ammeter that will test the alternator output and test for current draws. Make sure the one you but has it.

If you have an older car with a point equipped ignition system, you will need a dwell meter as well to measure and adjust the dwell angle of the points. As with any piece of equipment, read the instructions that come with your meter. It will tell you what the various functions are and how to connect the meter to the circuit for accurate test results. Most meters have a fuse in them to protect them from an incorrect connection. Make sure the one you buy has one and get a couple of spare fuses. You will, at some point, hook it up wrong and be very thankful you have the spares. I know I have.

Most of the troubleshooting on today's cars will be electrical in nature. A good wiring diagram is essential to properly troubleshoot any electrical circuit. They usually come in two parts, a schematic and the wiring diagram. The schematic shows the different components of a system and how they relate to each other. The wiring diagram shows the actual wire colors and connections.

For testing the mechanical side of the engine, you will need some more specialized equipment. A vacuum gauge with several adapters can be used to test manifold vacuum and test vacuum operated circuits. A hand vacuum pump is handy for testing vacuum operated components such as EGR valves and heating and air conditioning systems.

A compression tester is a must for testing your engines compression. The best type is the one that screws into the spark plug hole. They will give a more accurate reading then the ones you push against the spark plug hole. When doing a compression test, look for the uniformity between cylinders more than the actual compression. All the cylinders should be within 10% to 15% of each other.

Spark Plugs Tell A Story
Sample Diagnostic Tree

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Additional Information provided courtesy of
ALLDATAdiy.com and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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