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Diagnostics of the engine with vacuum gauge application
Use of the gauge at relatively low cash costs provides a fairly capacious information about the internal state of the engine. The results of the measurements can get an idea of the degree of wear of piston rings and cylinder bores, to identify the signs of failure of head gaskets and intake manifold, violations of regulations of the carburettor and cross-exhaust system, jamming or burnout valves subsidence valve springs, installation fails angle ignition timing and valve timing, ignition system failure, etc. etc.
Unfortunately, the results taken with the gauge readings easy to misinterpret, and therefore, they should be analyzed together with the data obtained in the course of other diagnostic tests.
When reading an indicator gauge should pay attention not only on the absolute value of the deviation of the arrow, but also on the speed of its movement. Most of the imported meters show the depth of depression in inches of mercury. It should be borne in mind that all regulatory requirements are given for the case of performance audits at zero altitude. Increased relief for every 300 m mark after 600 meters leads to an underestimation of the readings of about 1 inch Hg. Art. Note that 1 inch = 25.4 mm.
 | Connect the gauge directly into the inlet pipeline - not to the throttle body. Make sure that in the course of testing all hoses remained connected, - otherwise the taking of evidence can not be considered reliable. |
Before the measurements, the engine warm up to normal operating temperature. Support the wheel chock and cock a lay brake. Put the transmission in "P" position, start the engine and leave it running at normal idle speed.
 | Before starting the engine, carefully check the fan blades for cracks and other damage. Try not to approach the impeller arms and meter. Also avoid taking a position directly in front of the car! |
 | Consider the testimony of the gauge. The average depth of the depression in the intake manifold serviceable engine must be sufficiently stable (without jerks arrows) and is about 17 ÷ 22 inches (432 ÷ 560 mm) Hg. Art. The following paragraphs provide a scheme of interpretation takes readings: |
Low reading stability can be a sign of leaks through the gasket between the intake manifold and cylinder head, or else between the pipeline and the throttle body. There is also the likelihood of leakage of the vacuum hose failure, the ignition timing (in the direction of the lag), or violations of the timing. Check the ignition timing with a timing light, then turn eliminate all other possible causes, perform the checks in this chapter, only then it makes sense to remove the timing cover to verify the correctness of combination of adjusting labels.
If the result is 3 ÷ 8 inches (76 ÷ 203 mm) Hg. Art. below normal and thus fluctuations take place, the reason for this deviation may be a violation of tightness of a lining of the inlet pipeline in the area of the inlet port, a fault injector fuel injection.
Regular deflection meter down from the stable reading on 2 ÷ 4 inches (51 ÷ 102 mm) Hg. Art. with a high degree of probability testifies to leaks valves. Check the compression pressure in the cylinders or perform the test for leaks.
Irregular deviations or reset may be related to the jamming of valves or misfire. Measure the compression pressure, perform the test for leaks, check the condition of the spark plugs.
Frequent vibration indicator arrow within the range of 4 inches (102 mm) Hg. Art. while idling the engine, accompanied by smoke emissions from the exhaust pipe, speaks about deterioration of valve guides. Test the leak. If the needle vibrates at higher engine speeds, check for signs of leakage gasket intake manifold and cylinder heads. Please rate the degree of subsidence valve springs, check for signs of burnout valves and try to identify the misfiring.
Minor fluctuations in the readings within a range of one to two inches (25 ÷ 51 mm) Hg. Art. It can be regarded as evidence of infringement of serviceability of functioning of the ignition system. Verify that all of the usual adjusting installations, if necessary, resort to testing with analyzers ignition.
In the presence of fluctuations arrow meter in a wide range of compression pressure check or perform the test for leaks in order to identify the defective cylinder or infringement of tightness of the cylinder head gasket.
If the needle meter with slow speed "walking" in a wide range of the scale, check the patency of PCV and the mix of idling, and make sure there are no leaks through the gasket carburetor / throttle body and intake manifold.
Evaluate the rate of return to its original value when closing the throttle after raising the engine speed to a value of about 2500 rev / min due to rapid priotkryvaniya flap. First reading should drop to near zero, then rise above the values characteristic of the normal idling speed by about 5 inches (130 mm) Hg. Art. and to return to the idle indication. If the depth of the vacuum recovered slowly and does not form a peak throw at sharp closing the throttle, check, whether are not worn piston rings. In the long delay return of indications check the patency of the exhaust system (often blocked muffler or catalytic converter) - easiest to just disconnect suspected section of the exhaust system and repeat the test.
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