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ENGINE DIAGNOSIS AND FAULT ANALYZING METHODS

 

Modern engines are equipped with intricate units that act as brain or memory parts of the engine. Some of them these unit have sensors and actuating devices for some automatic functions. When dealing with some computer-controlled engines such as the ones mentioned earlier, certain components must be disconnected before attempting the power balance test. However, it is important to always check the service manual for appropriate procedures.

It is not healthy to run the engine with a shorted cylinder for more than 15 seconds because the unburned fuel in the exhaust can build up in the catalytic converter and create an unsafe situation, instead run the engine for at least 10 seconds between cylinder shorting.

It is necessary to override the controls of the electric cooling fan by using jumper wires to make the fan run constantly. If the fan control cannot be bypassed, disconnect the fan.

Connect the engine analyzer’s leads, then turn the engine on and allow it to reach normal operating temperature then reset the engine speed at 1,000 rpm and connect a vacuum gauge to the intake manifold. As each cylinder is shorted, note and record the rpm drop and the change in vacuum.

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As each cylinder is shorted, a noticeable drop in engine speed should be noted. Little or no decrease in speed indicates a weak 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, there is a problem. Further testing may be required to identify the exact cause of the problem.

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VACUUM TESTS

One way to diagnose the condition of an engine is through the measuring of intake manifold vacuum. The manifold vacuum test can be conducted with a vacuum gauge. The method involves forming a vacuum through the downward movement of the pistons during their intake stroke. If the cylinder is sealed, a maximum amount will be formed. High vacuum improves volumetric efficiency.

The vacuum gauge readings can be interpreted to identify many engine conditions, including the ability of the cylinder to seal, the timing of the opening & closing of the engine’s valves, and ignition timing. Normally, each cylinder of an engine will produce the same amount of vacuum; therefore, the vacuum gauge reading should be steady and give a reading of at least 17 inches of mercury.

When one or more cylinders produce more or less vacuum than the others, the needle of the gauge will fluctuate. The intensity of the fluctuation is proportional to the problem. For instance, when the reading of the vacuum gauge fluctuate between 10 and 17 inches of mercury, we should look at the rhythm of the needle.

If the needle seems to stay at 17 most of the time but reduces to 10 and quickly increase again, then the reading is probably caused by a problem in one cylinder. Low reading or fluctuating could indicate many problems. For instance, a low, steady reading might be caused by retarded ignition timing or incorrect valve timing. A sharp vacuum drop at regular intervals might be caused by a burned intake valve. Other conditions that can be revealed by vacuum readings follow:

Stuck or burned valves

Improper valve or ignition timing

Weak valve springs

Faulty PCV, EGR, or another emission-related system

Uneven compression

Worn rings or cylinder walls

Leaking head gaskets

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Vacuum leaks

Restricted exhaust system

Ignition defects

 

OIL PRESSURE TESTING

An oil pressure test is used to determine the wear of an engine’s parts. The oil pressure test is performed with an oil pressure gauge, which measures the pressure of the oil as it circulates through the engine. Basically, the pressure of the oil depends on the efficiency of the oil pump and the clearances through which the oil flows. Excessive clearances, most often caused by wear between a shaft and its bearings, will cause a decrease in oil pressure.

Loss of performance, excessive engine noise, and poor starting can be caused by abnormal oil pressure. When the engine’s oil pressure is too low, premature wear of its parts will result. An oil pressure tester is a gauge with a high-pressure hose attached to it. The scale of the gauge typically reads from 0 to 100psi.

Using the correct fittings and adapters, the hose is connected to an oil passage in the engine block. Normally, the engine’s pressure sensor is removed and the hose is connected to that port. Here is a procedure for the conducting of the test; first, simply follow the guidelines given in the service manual and observe the gauge. The pressure is read when the engine is at normal operating temperatures and at a fast idle speed.

To get accurate results from the test, ensure you follow the handbook manual and manufacturer’s recommendations. Compare your findings with the specifications. Excessive bearing clearances are not the only possible causes for low oil pressure readings; others are pump-related problems, a plugged oil pickup screen, a weak or broken oil pressure relief valve, low oil level, contaminated oil, or low oil viscosity. Too much oil, cold oil, high oil viscosity, restricted oil passages, and a faulty pressure regulator can cause high oil pressure readings.

 

 

 

Originally posted 2018-11-21 18:13:58.

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