How to use cylinder pressure gauge? How to use cylinder pressure gauge

Because the instrument has the advantages of simple structure, small size, light weight, low price and reliable use, it is widely used in automobile maintenance companies to detect cylinder pressure.





Structure and working principle of cylinder pressure gauge
The cylinder pressure gauge is a special pressure gauge for gas, which generally consists of a pressure gauge head, a conduit, a one-way valve and a joint. Most of the pressure gauge heads are of the Bourdon-tube type. The driving element is a flat tube bent into a circle, with one end as a fixed end and the other end as a movable end. The movable end is connected to the meter pointer through a lever and gear mechanism. When gas pressure enters the elbow, the elbow straightens. Therefore, the lever and gear mechanism drive the meter pointer to swing, indicating the gas pressure on the dial.



There are two types of connectors for cylinder pressure gauges. One is a threaded pipe joint that can be tightened into the threaded hole of the spark plug or injector;the other is a tapered or stepped rubber joint that can be pressed onto the spark plug or injector hole by hand. The connector is connected to the pressure gauge head through a conduit. There are also two types of conduits, one is a soft conduit and the other is a metal hard conduit. The soft conduit is suitable for the connection between the threaded pipe joint and the pressure gauge head, and the hard conduit is suitable for the connection between the rubber joint and the gauge head.



The cylinder pressure gauge conduit is also equipped with a one-way valve that can pass to the atmosphere. When the one-way valve is in the closed position, the pressure gauge pointer can be kept in a test state for easy reading. When the one-way valve is in the open position, the pressure gauge pointer can be returned to zero for retesting.

How to use cylinder pressure gauge? How to use cylinder pressure gauge


① Testing conditions


The engine should be run to normal operating temperature;use the starter to drive the engine with all spark plugs or injectors removed, and its speed should comply with the original manufacturer's specifications.



②Detection method


Remove the engine air filter, use compressed air to blow away the dirt around the spark plugs or injectors, remove all spark plugs or injectors, and place them in order by the cylinder. For gasoline engines, the secondary high-voltage bus of the ignition system should also be unplugged from the distributor end and reliably grounded to prevent electric shock or fire. Then, insert the rubber joint of the cylinder pressure gauge into the spark plug or injector hole of the cylinder under test, straighten it and tighten it.
Place the throttle valve (including the choke valve if it has a choke valve) in the fully open position, use the starter to rotate the crankshaft for 3 to 5 seconds (not less than four compression strokes), and stop after the cylinder pressure gauge pointer indicates and maintains the maximum pressure. Turn. Remove the cylinder pressure gauge, record the reading, and press the one-way valve to return the cylinder pressure gauge pointer to zero.


Measure each cylinder in sequence according to the above method, with no less than two measurements per cylinder, and the arithmetic average of the measurement results of each cylinder is taken.


When testing the diesel engine cylinder pressure while on the vehicle, a pressure gauge with a threaded joint should be used. If the machine requires measurement at a higher speed, all cylinders except the cylinder under inspection should be working (the injector cannot be removed). Other testing conditions and testing methods are the same as those for gasoline engines.





Cylinder pressure diagnostic parameter standard
For automobile engines in use, in accordance with the national standard gb18565-2001 "Comprehensive Performance Requirements and Inspection Methods for Commercial Vehicles", the pressure of each cylinder of the engine should not be less than 85% of the original design specified value;the difference between the pressure of each cylinder and the average pressure of each cylinder : Gasoline engines should be no more than 8%, diesel engines should be no more than 10%.
For engines that have been overhauled, in accordance with the provisions of Appendix B of the national standard gb/t15746.2-1995 "Automotive Repair Quality Inspection and Assessment Standards Engine Overhaul": the cylinder pressure of the engine that has been overhauled should comply with the original design regulations;the pressure of each cylinder should be the same as the average of each cylinder The difference in pressure: no more than 8% for gasoline engines and no more than 10% for diesel engines.





Cylinder pressure result analysis
If the measurement result of the cylinder pressure is higher than the original design value, it does not necessarily indicate that the cylinder sealing is good. It must be analyzed based on the use and maintenance conditions. This situation may be caused by excessive carbon deposits in the combustion chamber, the cylinder liner is too thin, or the joint plane of the cylinder block and cylinder head has been repaired and processed too much for many times. If the cylinder pressure measurement result is lower than the original design value, it means that the cylinder sealing is reduced. You can inject a small amount of engine oil into the spark plug or injector hole of the cylinder, and then use the cylinder pressure gauge to measure the cylinder pressure again for in-depth diagnosis and recording.
if:


① The second measurement result is higher than the first and is close to the standard pressure, indicating that the cylinder, piston ring, and piston are excessively worn, or the piston ring is aligned, stuck, broken, and the cylinder wall is strained, causing the cylinder to be unsealed.