Powerbuilt 648744 Manual De Instrucciones página 4

TROUBLESHOOTING AUTOMOTIVE VACUUM SYSTEMS
Automotive vacuum systems consist of a vacuum source, lines, hoses and fittings, and vacuum units or components. This system must be free from leaks. If leaks occur, the air/fuel
mixture of the engine may be changed by the additional air entering the engine. This may result in poor engine performance and lead to damage to the engine internal components
over time.
Trouble with vacuum systems can most often be determined to be one of the following problems:
1. Leaks - Leaks occur in hoses, connectors, tees, diaphragms and valves. Most often the leak occurs at the end of the vacuum line where it attaches to a component. The hose
becomes hard at the hose end and splits, no longer sealing the connection. Often cutting off a small piece at the hose end will temporarily solve the problem. The hose should
eventually be replaced.
2. Blockage - Blockage occurs when vacuum lines are pinched or full of foreign material, when valves are clogged or stuck, or when some other problem occurs that prevents air from
flowing. Clearing the line and/or freeing up stuck valves should solve the problem.
3. Failed component - A visual inspection of vacuum devices can be important to determining their correct operation. It is important to have manufacturer's service information available
to determine the location and proper function of vacuum components. Often tests are provided that will allow you to determine whether a component is leaking, has failed, or is
functioning properly.
ENGINE MECHANICAL CONDITIONS
Reading the gauge on the vacuum pump can help diagnose a variety of engine conditions.
With the pump connected to the appropriate component or vacuum line, read the measured amount of vacuum at the gauge (engine running). Do NOT pump the handle, as this will
cause an incorrect reading.
In order to put the vacuum gauge to good use, we must understand how it works and what the readings can tell us. A vacuum gauge measures the difference of pressure in the intake
manifold and the actual atmospheric pressure. Vacuum is a pressure that is below atmospheric pressure.
For instance, zero on your vacuum gauge would represent 14.7-psi at sea level. As the engine is cranked, the piston of each cylinder will create a partial vacuum during its intake stroke.
This results in lower manifold pressures. Any leaks in cylinder sealing will increase manifold pressure. A cylinder that is not sealing properly will not produce sufficient compression
pressures. We need to raise combustion chamber pressures and the resulting temperatures for reliable ignition.
An engine in good mechanical condition, depending on its size, will typically develop somewhere between 17 and 21 in. Hg at 1000 rpm.
Low Vacuum: A low steady vacuum reading at idle could indicate a problem with an external vacuum leak. Another cause could be late ignition or valve timing. If adjusting the ignition
timing to specification does not increase the vacuum gauge reading, the valve timing should be checked.
Cranking: During cranking speeds, we should develop between 3 to 5 in. Hg with the throttle closed. This is a good test for an engine that will not start. A reading of zero would indicate
there is an internal engine problem. A quick test here can save a lot of diagnostic time.
Base Idle: A quick check to see if the base idle screw of a fuel-injected vehicle has been tampered with is as follows. Hook up your vacuum gauge to ported vacuum on the throttle body
at idle. There should be almost zero vacuum.
Restricted Exhaust (Catalytic Converter): When the engine is unable to exhale properly, a positive pressure will develop inside the cylinder each time the exhaust valve opens. This
increases the pressure inside the intake manifold as the intake valve opens. The end result is lower manifold vacuum. See Figure: Restricted Exhaust.
Run the engine at 1000 rpm and record the vacuum reading. Increase engine speed slowly to 2500 rpm. Exhaust backpressure, depending on the amount of restriction, will increase
with engine rpm. If the vacuum reading at 2500 rpm should drop more than 3 in. Hg from the reading taken at 1000 rpm, the exhaust system is most likely restricted.
Worn Piston Rings: When piston rings are sealing properly, manifold vacuum will increase above a normal level whenever the throttle is quickly snapped closed. The closed throttle with
high piston speed will create a large pressure differential in the intake manifold. If rings are worn out, the gauge should drop to zero, then rize to 22 in. Hg when the throttle is rapidly
depressed and then released. See Figure: Worn Piston Rings.
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