2 Basic Tests For a Rough Running Engine
Posted: Friday, November 28, 2008
by Mark Gittelman
certifiedmastertech.com
When faced with a rough running engine , many do-it-yourself mechanics begin to look for the answers in the vehicle's high tech systems. In many cases, the actual problem lies in the basic principles of engine operation. Not all engine performance problems are related to electronic control systems. Therefore a car mechanic still needs to understand basic engine testing procedures . These tests are an important part of modern engine diagnosis.
Compression test for rough running engines
Why perform a compression test ? Internal combustion engines depend on the compression of the air fuel mixture to maximize the power produced by the engine. The upward movement of the piston on the compression stroke will compact the air fuel mixture within the sealed combustion chamber raising the temperature of the charge and making it easy to ignite and burn completely.
An engine with poor compression or low compression will not run correctly and cannot be tuned properly. If a rough running engine condition is present, this could be a symptom that suggests the cause of the problem may be poor compression. A compression gauge is used to check the cylinder sealing capabilities. This is an easy to use inexpensive tool that comes with complete instructions on how to use it.
Power balance test
Diagnose a rough running engine with A power balance test . This is performed quickly and easily using an engine analyzer, because pushing a button can automatically or manually control the firing of the spark plugs. Some vehicles have the power balance test built into the engine control computer. This test is either a part of a routine self-diagnostic operating mode or must be activated by the mechanic through a scan tool. These types of vehicles will often use these functions to set engine misfire codes.
On some computer controlled engines certain components must be disconnected before attempting a power balance test. Always check the service manual for appropriate procedures. Be careful not to run the engine with a shorted cylinder for more than 10 or 15 seconds. The unburned fuel in the exhaust can damage the catalytic converter and create an unsafe situation. It is also a good idea to run the engine on all cylinders for a minute before proceeding to the next cylinder.
As each cylinder is shorted, a noticeable drop in engine speed should be detected. Little or no decrease in RPMs indicates a week cylinder. If all of the readings are fairly close to each other, the engine is in good condition. If the readings from one or more cylinders differ from the rest then a problem should be looked into on that cylinder.
Mark the mechanic provides information on many more engine testing procedures on his website. He also recommends that you brush up on the operational principles of automotive engines.
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Top-level comments on this article: (3 total)Great help to me. Thanks and keep up the good job. chris from Nigeria
Mark, good article. If I may, I will also recomend a quik vacum test before a compresion test which will also help you diagnose other problematic areas.Pedro Talavera from CMT of Miami.Pedro: I agree with you on the vacuum test being important as well. In fact this would seem to be a great subject for my next article. Thanks for stopping by and for your comments!Good to be of help. Keep churning those great articles Mike,Pedro.
my car has no check engine light on i just did the timing to make sure that wasnt it i check the time five times its right whare it should be. im not sure whare to go from here plugs wires are all good
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