PlugIn "Phase measurement"
PlugIn "Phase measurement" displayes the cylinder pressure waveform (the voltage waveform of the output signal of the pressure transducer in the cylinder) in a window of the program "USB Oscilloscope" when the engine at idle, marks the moments when the piston of the diagnosed cylinder is in the top/bottom dead centers (0°, 180°, 360°, 540°). Besides PlugIn highlights an admissible range for position of four characteristic points and sites of the waveform (D, E, I, L), which positions depend on mutual position crankshaft and camshafts.
PlugIn "Phase measurement".
Measurement of position of characteristic points and sites of the pressure waveform in the cylinder allows to judge correctness of mutual position crankshaft and camshafts.
Point 0°.
Position of the piston when it is on the most close distance from the cylinder head, name the Top Dead Center (TDC). The moment when the piston is in TDC and simultaneously intake and exhaust valves are closed, noted as 0°. The power stroke begins with this moment.
When the piston is in position TDC 0°, value of the pressure in the cylinder achieves the maximum. Sometimes this pressure name a dynamic compression.
Point D.
The exhaust valve of the petrol engine starts to open earlier, than the piston will achieve the bottom dead center. Thus the piston still goes away from the cylinder head and the volume between the piston and the cylinder head continues to increase, but absolute pressure in the cylinder starts to increase. Increasing of pressure in the cylinder occurs because the exhaust gases start to flow from the exhaust manifold into cylinder through the exhaust valve which opens. The point of the pressure waveform in the cylinder since which the exhaust gases start to flow into cylinder from the exhaust manifold, is noted by letter D.
It is possible to check correctness of mutual position of the exhaust camshaft and crankshaft of the petrol engine by position of point D.
If point D (the beginning of opening of the exhaust valve) is in range 130°…160° after TDC 0° (50°…20° before BDC 180°), the moment of the beginning of opening of the exhaust valve consider installed correctly.
Point D.
PlugIn "Phase measurement" is highlighted the range 130°…160° after TDC 0° of the pressure waveform in the cylinder in a window of the program "USB Oscilloscope" and is noted by letter D.
Site E.
The flowing of gases from the exhaust manifold to the cylinder occurs because the absolute pressure in the exhaust manifold, approximately equals atmospheric pressure, is greater then the absolute pressure in the cylinder. The site of the pressure waveform in the cylinder where there is an flowing of the exhaust gases from the exhaust manifold to the cylinder, is noted by letter E.
It is possible to check correctness of mutual position of the exhaust camshaft and crankshaft of the petrol engine by position of the center of site E.
If the center of site E is in range 170°…195° after TDC 0° (-10°…+15° from BDC 180°), the moment of opening of the exhaust valve consider installed correctly.
Site E.
PlugIn "Phase measurement" is highlighted the range 170°…195° after TDC 0° of the pressure waveform in the cylinder in a window of the program "USB Oscilloscope" and is noted by letter E.
Point 180°.
Position of the piston when the distance from it to the cylinder head is maximal, name the Bottom Dead Center (BDC). In BDC the piston stops, and changes the direction of movement to the opposite, started again to come to the cylinder head. The moment when the piston is in BDC and the intake valve is closed, and the exhaust valve is opened (or has started to open) is noted as 180°. Since this moment the piston starts "to push out" gases from the cylinder to the exhaust manifold.
Point 360°.
Achieved the second top dead center in the end of the exhaust stroke, the piston stops, and changes the direction of movement to the opposite, started again to goes away from the cylinder head. The moment when the piston is in the second TDC is noted as 360°. Since this moment the piston stops "to push out" gases from the cylinder to the exhaust manifold, and starts "to suck in" from an intake manifold the air/fuel mixture to the cylinder.
Site I.
When the piston has achieved point TDC 360° and has changed a direction of movement to the opposite, the exhaust valve is already almost closed. Owing to closing the channel connecting internal volume of the cylinder with the exhaust manifold, pressure inside the cylinder stops to equalizing with pressure in the exhaust manifold. The intake valve already has a slightly opened the channel of the air/fuel mixture and continues to open. Because the channel connecting internal volume of the cylinder with an intake manifold has started to open, pressure in the cylinder starts to equalizing with pressure in an intake manifold. As the value of absolute pressure in the cylinder is approximately equals atmospheric pressure, gases from the cylinder start to flow from the cylinder to the intake manifold, where pressure considerably below atmospheric.
The site of the pressure waveform in the cylinder where is the flowing of gases from the cylinder to the intake manifold is noted by letter I. By position of the center of site I it is possible to check correctness of mutual position of the intake camshaft and crankshaft of the petrol engine.
If the center of site I is in range 370°…390° after TDC 0° (±10° from the mark 380° after TDC 0°), the moment of opening of the intake valve consider installed correctly. On variable valve timed engines (equipped with the system VVT) the center of site I should be in range 380°…400° after TDC 0° (±10° from the mark 390° after TDC 0°).
Site I.
PlugIn "Phase measurement" is highlighted the range 370°…390° after TDC 0° at the switched off option "VVT" on the PlugIn panel or a range 380°…400° after TDC 0° at the switched on option "VVT" (the option "VVT" should be switched on at variable valve timed engines). The range is noted by letter E.
Point 540°.
After achievement of the second bottom dead center the piston stops, and changes the direction of the movement to the opposite, started again to come nearer to the cylinder head. The moment when the piston is in BDC and the exhaust valve is closed, and the intake valve is opened (or has started to close) is noted as 540°. Since this moment the piston stops "to suck in" the air/fuel mixture from an intake manifold to the cylinder. But at high RPM filling of the cylinder by air/fuel mixture does not stop due to inertia of a stream of a mixture.
Point L.
The intake valve of the petrol engine closes a little after the moment of achievement by the piston of the second bottom dead center 540°. The pressure waveform in the cylinder in the area of closing of the intake valve is defined by a direction of movement of a mixture on the inlet channel directly ahead of the moment of closing of the intake valve.
At high RPM, before the moment of closing of the intake valve there is an effect of superfluous filling of the cylinder by the air/fuel mixture due to inertia of a stream of a mixture, and pressure in the cylinder starts to increase already from the moment of achievement by the piston of the bottom dead center 540°. With closing the intake valve, after a site concerning intensive increase of pressure in the cylinder there is an appreciable crisis of the waveform - since this moment velocity of increase of absolute pressure in the cylinder sharply decreases.
At low RPM appears the effect of the flowing of the mixture which has arrived earlier to the cylinder back to an intake manifold and as a consequence the pressure in the cylinder does not increase to the moment when intake valve does not close. With closing the intake valve, after flat site there is an appreciable crisis of the waveform - since this moment, absolute pressure in the cylinder starts to increase rather intensively.
The moment of closing of the intake valve is noted by letter L. Since this moment the piston starts to compress gases in the cylinder.
It is possible to check correctness of mutual position of the intake camshaft and crankshaft of the petrol engine by position of the point L.
If point L (the end of closing of the intake valve) is in range 560°…600° after TDC 0° (20°…60° after BDC 540°), the moment of the end of closing of the intake valve consider installed correctly.
Point L.
PlugIn "Phase measurement" is highlighted the range 560°…600° after TDC 0° of the pressure waveform in the cylinder in a window of the program "USB Oscilloscope" and is noted by letter L.
The order of connection transducers.
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In case if the diagnosed engine is equipped by the distributed fuel injection system, it is urgently recommended to disconnect a socket from an electromagnetic fuel injector of the diagnosed cylinder and to connect to the disconnected socket the resistor with the value 100Ω (connection of the resistor will prevent preservation of the error of type "injector ¹… circuit damaged" to the fault codes memory of the engine control module). In case of performance of this recommendation, fuel will not inject to the diagnosed cylinder during carrying out of diagnostics. In case if this recommendation is not executed, during carrying out of diagnostics probably occurrence of thermal ignition of the air/fuel mixture in the diagnosed cylinder, that can become the reason of damage of the pressure transducer in the cylinder. Besides not burned fuel from the diagnosed cylinder will penetrate to an exhaust system and the overheat and damage the catalyst neutralizer of the diagnosed car is possible.
If submission of fuel to the diagnosed cylinder is not preventable, for decreasing probability of occurrence of thermal ignition of air/fuel mixture in the diagnosed cylinder of the hot engine it is necessary to unscrew a spark plug from the diagnosed cylinder and to wait not less than 10 minutes before to install the pressure transducer upon a place of a spark plug. In order to prevent damage the catalyst neutralizer, it is recommended to reduce up to a minimum duration of carrying out of diagnostics in this mode; - install the pressure trasducer Px on a place of a spark plug of the diagnosed cylinder and connect it to the 1-st analog input of USB Autoscope III;
- connect the high-voltage wire of the diagnosed cylinder to the spark gap with a spark interval no more 5mm;
- connect the black "crocodile" clip from the pressure transducer to "ground" of the engine block;
- connect the red "crocodile" clip from the pressure transducer to the terminal "+" of the vehicle battery of the diagnosed car;
- start the program USB Oscilloscope;
- choose "Control => Load user preset => Px";
- start the engine of the diagnosed car. PlugIn "Phase measurement" will start to display the pressure waveform in the cylinder after an establishment of stable idle RPM.
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The displayed signal can be written down simultaneously. For this purpose it is necessary to choose in the menu "Control" item "Record". The written waveform can be seen and if necessary to saved. For saving of the waveform in the menu "File" it is necessary to choose item "File Save As..".