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Automotive Diagnostics
Automotive diagnostics Despite the sophistication of today's power train control systems, even the most advanced software program can not diagnose a worn camshaft Lobe, a burned valve, or loose timing chain. Unfortunately, even though these types of mechanical failures create recognizable symptoms of poor performance, many technicians get caught up analyzing or over analyzing computer-controlled systems. When the root failure is related to a mechanical or hard part failure. Automotive diagnostics used to uncover diagnostic trouble codes, may actually be the result of faulty mechanical components. That's why it is important to follow a logical diagnostic routine. In this article we'll take a look at just one basic automotive diagnostic troubleshooting procedure that can effectively isolate the root cause of many power train related failures. Simple automotive diagnostics. Checking vacuum, while it may be low tech a vacuum gauge is a powerful diagnostic tool that can help you quickly determine an overall engine's performance. Engine vacuum is simply a condition in which the pressure of gas. In this case air is less than the normal atmospheric pressure at sea level atmospheric pressure is approximately 14.75 psi, which corresponds to a barometric pressure of 29.5 inches of mercury. This means that if you placed a long tube into a bowl of liquid mercury and remove the air from the opposite end the surrounding air pressure would force the Mercury almost 30 inches up the two. This works out to 2 inches of mercury for every one psi of air pressure.
Using vacumm for automotive diagnostics
Understanding the relationship between pressure and vacuum is important to avoid misinterpretation of automotive diagnostics. The OBD to automotive sensor that measures vacuum is the map sensor or manifold absolute pressure.
With the key on and the engine off the map reading will be about 29.5 inches of mercury, which is the equivalent of atmospheric pressure at sea level. Once the engine is idling the map sensor reading will drop to about 11.5 inches of mercury. At first glance, you may think that this reading is indicative of a serious mechanical problem.
However, while this may appear to be a low vacuum reading. It is actually a normal pressure reading. Remember that map sensor voltage is measured in pressure and not vacuum. To determine actual engine vacuum simply subtract the running map sensor value from the key on the engine off value.
This means that if the running value is 11.5 inches of mercury actual engine vacuum is 18 inches. A healthy engine will typically produce between 18 and 20 inches of vacuum at idle with closed throtle and no engine load. With this baseline measurement in hand automotive diagnosis can now be continued.
Mark is willing to share more automotive information with you at his do it yourself auto repair web site. A good place to start is an article on troubleshooting your own car problems. A close second would be some tips on using troubleshooting manuals for increased chances of success.
Using vacumm for automotive diagnostics
Understanding the relationship between pressure and vacuum is important to avoid misinterpretation of automotive diagnostics. The OBD to automotive sensor that measures vacuum is the map sensor or manifold absolute pressure.
With the key on and the engine off the map reading will be about 29.5 inches of mercury, which is the equivalent of atmospheric pressure at sea level. Once the engine is idling the map sensor reading will drop to about 11.5 inches of mercury. At first glance, you may think that this reading is indicative of a serious mechanical problem.
However, while this may appear to be a low vacuum reading. It is actually a normal pressure reading. Remember that map sensor voltage is measured in pressure and not vacuum. To determine actual engine vacuum simply subtract the running map sensor value from the key on the engine off value.
This means that if the running value is 11.5 inches of mercury actual engine vacuum is 18 inches. A healthy engine will typically produce between 18 and 20 inches of vacuum at idle with closed throtle and no engine load. With this baseline measurement in hand automotive diagnosis can now be continued.
Mark is willing to share more automotive information with you at his do it yourself auto repair web site. A good place to start is an article on troubleshooting your own car problems. A close second would be some tips on using troubleshooting manuals for increased chances of success.
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, Nov 3 2007, 11:51 AM EDT
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