Automobile Inspection Technology

Chapter 8 Automotive Engine Detection (4)
The ignition timing instrument used to detect the ignition advance angle by the stroboscopic method is also called a timing light, as shown in Figure 2-23.The instrument is composed of a flash lamp, a sensor, a shaping device, a delay trigger device and a display device. It uses the principle of synchronizing the flash moment with the ignition of the I cylinder to measure the ignition advance angle of the engine. Its basic working principle is based on the stroboscopic principle. .That is: if at precisely determined time, relative to the angle of rotation of the rotating part, a beam of short (about 1/5000s) pulses with the same frequency as that of the rotating part is irradiated, due to the physiological inertia of people's vision, it seems that the part does not rotate of.

The ignition timing detector made by the flash method can be made into a single-function portable, and can be combined with other instruments to form a multi-functional comprehensive type (such as an engine comprehensive performance test bench).Its indicating device can be either a pointer type or a digital type, and some have a printout function.

When the indicating device has the function of measuring the speed and displaying the instantaneous speed, the ignition advance angle of the engine can be measured at the specified speed.

When testing, first connect the two power clips of the timing light to the positive and negative electrodes of the battery, and then connect the ignition pulse sensor in series between the spark plug of a cylinder and the high voltage line or externally clamp it on the high voltage line of a cylinder (inductive sensor) ;Turn the potentiometer of the timing light to the initial position, turn on the switch, the timing light should flash, and the indicating device should indicate the zero position; wipe the flywheel or crankshaft pulley to make it clearly show the timing mark; put the engine at idle speed Turn on the timing light and align it with the official mark; adjust the potentiometer knob so that the active mark is aligned with the fixed mark, and the reading displayed at this time is the ignition advance angle under the idling condition.The same method can be used to measure the ignition advance angle under different working conditions.

When the engine is running at idle speed, the centrifugal and vacuum ignition advance devices do not work or have little effect, and the ignition advance angle measured at this time is the initial advance angle.If the ignition advance angle measured under each working condition meets the regulations, it means that the initial ignition advance angle is adjusted correctly, and at the same time, it means that the centrifugal ignition advance device and the vacuum ignition advance device are working normally.It can also test the centrifugal advance angle and vacuum advance angle under various working conditions.Remove the vacuum hose of the vacuum advance device of the distributor and use it when the vacuum advance device does not work. The centrifugal advance angle at various speeds can be obtained by subtracting the initial ignition advance angle from the ignition advance angle at various speeds; When the vacuum hose of the vacuum advance device is connected, the vacuum ignition advance angle can be obtained by subtracting the centrifugal advance angle and the initial advance angle from the ignition advance angle measured at the same speed.

For the computer-controlled electronic ignition system, the detection of its ignition advance angle should be carried out according to the steps of calibrating the ignition timing specified by the manufacturer.The ignition advance angle of the electronically controlled ignition system includes three parts: the initial ignition advance angle, the basic ignition advance angle and the corrected ignition advance angle.Among them: the basic ignition advance angle is the most important part of the ignition advance, and its size depends on the engine operating conditions.When testing, generally the ignition timing inspection terminal under the engine hood should be grounded first, so that the computer-controlled ignition advance does not work.First detect the basic advance angle (that is, the ignition advance angle when the engine automatic control ignition advance device does not work), and then remove the ground wire after the detection.Please refer to the instructions for specific detection methods and steps.Table 2-3 shows the basic ignition advance angles of engines of common models.The principle and method of using the flash lamp to detect the ignition advance angle of the electronically controlled fuel injection engine are the same as those of the traditional engine.

2. Cylinder pressure detection

When the piston of a certain cylinder reaches the top dead center of the compression stroke, the compression pressure in the cylinder is the highest.Use the cylinder pressure sensor to detect this moment, and use the ignition sensor to detect the ignition moment of the same cylinder at the same time, and the corresponding crankshaft angle between the two is the ignition advance angle.The ignition timing detector made by the cylinder pressure method is composed of a cylinder pressure sensor, an ignition sensor, a processing device and an indicating device.If the ignition timing detector has an oil pressure sensor, it can also be used to detect the fuel supply advance angle of the diesel engine.The ignition timing tester made by the cylinder pressure method is not only portable with a single function, but also can be combined with other instruments to form a multifunctional comprehensive type.Many types of engine comprehensive detectors (such as domestic QFC-4 and WFJ-1, etc.) have the function of detecting engine ignition advance angle by cylinder pressure method.Figure 2-24 is a schematic diagram of detecting engine ignition or fuel supply advance angle by cylinder pressure method.

The detection steps when detecting the ignition advance angle of the engine with the ignition timing instrument made by the cylinder pressure method or the comprehensive engine detection instrument are as follows:
①Run the engine until it reaches normal operating temperature and then stop it.

②Remove the spark plug of a certain cylinder, and install the cylinder pressure sensor (Fig. 2-25) in the spark plug hole.

③Fix the removed spark plug on the body to ground it (note: the center electrode cannot touch the body), plug the ignition sensor on the spark plug, and connect the high-voltage line of the cylinder.At this time, the spark plug of this cylinder can ignite outside the cylinder.

④Start the engine. Since the measured cylinder is not working, the cylinder pressure signal output by the cylinder pressure sensor reflects the compression pressure of the cylinder. The maximum value is generated at the top dead center of the piston compression end. Pulse signal or ignition voltage waveform signal.

⑤ Operate according to the requirements of the instrument manual (for example, when using the WFJ-1 engine tester to measure the ignition advance angle, you need to key the operation code 08 and operate according to the prompts on the screen), and you can measure the idle speed, specified rpm or the ignition advance angle at either rpm.For the detector with printing function, after pressing the print button, the test result can also be printed out.

The cylinder pressure method is the same as the flash method, and can measure the initial ignition advance angle and the total advance angle, centrifugal advance angle, vacuum advance angle and basic ignition advance angle of the computer-controlled electronic ignition system under different working conditions.When detecting the ignition timing, generally only one cylinder (such as 1 cylinder) is measured, and the ignition advance angle of other cylinders is determined by the ignition interval, which can be obtained from the parallel waves displayed on the oscilloscope screen, and the computer-controlled ignition oscilloscope can directly display Out of the ignition gap.Then according to the ignition timing of the measured cylinder and the ignition interval of each cylinder, the ignition advance angle of other cylinders can be obtained.When the overlapping angle of the ignition waveform of each cylinder is small, it can be considered that the ignition interval of each cylinder is equal, so the ignition advance angle of other cylinders is the same as that of the measured cylinder, and the ignition advance angle of the measured cylinder is the ignition advance angle of the entire engine horn.

(Section [-]) Detection of diesel engine oil supply system

Detection of Fuel Injection Advance Angle

There are three methods for the detection of fuel injection advance angle: manual experience inspection and correction, cylinder pressure detection and stroboscopic detection.

1. Manual experience check and correction steps are as follows:
① Rotate the crankshaft so that the 1-cylinder piston is in the compression stroke. When the top dead center mark on the flywheel is aligned with the mark on the engine casing, stop the rotation.

② Check whether the engraved mark on the driven disc of the fuel injection pump coupling is aligned with the engraved line on the front face of the pump housing, as shown in Figure 2-26.If the two are aligned, it means that the fuel supply timing of the injector is correct; if the engraved line of the driven plate is in front of the fixed engraved line at the front end of the pump casing, the fuel supply to cylinder 1 is late; otherwise, the fuel supply to cylinder 1 is early.

③ When the oil supply to cylinder 1 is too early or too late, loosen the fixing screw of the universal joint of the fuel injection pump, align the movable mark with the fixed mark, tighten it, and start the engine for a road test.

④Choose a flat, hard straight road or a special runway as the test road for the fuel supply advance angle. After the car is hot, drive at the highest gear and the most stable speed, and then slam the accelerator pedal to the end to accelerate the car rapidly.If the diesel engine has a slight ignition knocking sound, which can disappear by itself in a short period of time, the fuel supply advance angle is correct; if the ignition knocking sound is strong and cannot disappear by itself in a short period of time, the fuel supply advance angle is too large ; If you can't hear the sound of ignition, knocking on fuel injection pump 1 cylinder to start fuel supply, and the acceleration is weak, and white smoke is emitted from the exhaust pipe, the fuel supply advance angle is too small.When the fuel supply advance angle of the engine is too large or too small, stop the car and loosen the fixing bolts of the universal joint of the fuel injector, make the camshaft of the fuel injection pump rotate in the reverse direction or along the direction of rotation a little and then fix it, and then test and debug repeatedly until the fuel supply timing is correct until.

2. Cylinder pressure detection

Using the engine comprehensive detector, the cylinder pressure method can be used to quickly detect the fuel supply advance angle of one cylinder or a certain cylinder of the engine. The basic principle is: use the cylinder pressure sensor to determine the maximum compression pressure point of a certain cylinder (that is, the top dead center of the cylinder piston) , use the oil pressure sensor to determine the oil supply time of the cylinder.The corresponding crankshaft rotation angle between the two is the value of the fuel supply advance angle of the cylinder, as shown in Figure 1-2.

When measuring, remove the fuel injector of the measured cylinder, and install a cylinder pressure sensor on its seat hole; connect the oil pressure sensor in series between the fuel injector of the measured cylinder and the high-pressure oil pipe as required, so that the fuel injector Spray fuel outward; stabilize the engine speed at the specified speed (800-1000r/min), select the button according to the requirements of the instrument manual, and the detection value of the oil supply advance angle of the measured cylinder can be displayed on the screen.

3. Stroboscopic detection

The fuel supply timing instrument for diesel engine made on the basis of stroboscopic principle, its composition, working principle and usage method are basically the same as gasoline ignition timing instrument (see this chapter (section [-])).

During detection, the oil pressure sensor of the fuel supply timing instrument is connected in series between the high-pressure fuel pipe of the 1st cylinder and the fuel injector or externally inserted into the high-pressure fuel pipe to convert the oil pressure pulse signal into an electrical signal and trigger the timing light to flash.One flash, one cylinder oil supply, both have the same frequency.Align the timing light with the top dead center mark at the end of compression of cylinder 1, and when it flashes synchronously with the fuel supply time, you can see that the fuel supply advance angle mark on the running flywheel or the crankshaft pulley is located before the fixed mark, indicating that the fuel supply to cylinder 1 is When the piston has not reached the top dead center, the oil supply time is before the piston reaches the top dead center.In order to measure the fuel supply advance angle, adjust the potentiometer on the timing light so that the strobe time is delayed from the fuel supply time, gradually make the fuel supply advance angle mark on the rotating parts approach the fixed mark, and align the two marks. The delay time of the flash is the fuel supply advance time, which can be displayed on the indicating device after being converted into the value of the fuel supply advance angle by the instrument.

The method of adjusting the fuel supply advance angle is as mentioned above, and the adjusted fuel supply advance angle should meet the original factory regulations.The fuel supply timing instrument can be used to detect and adjust, so that the fuel supply advance angle reaches the specified value.See Table 2-4 for the specified values ​​of fuel supply advance angles for common diesel automobile engines.

4. Oil supply interval detection of each cylinder

After the fuel supply advance angle of 1 cylinder is detected, if the fuel supply interval of each cylinder is equal according to the working sequence, the fuel supply advance angle of each cylinder is equal to the 1 cylinder fuel supply advance angle.Therefore, it is necessary to detect the fuel supply interval between each cylinder to know whether the fuel supply advance angle of each cylinder meets the requirements.When using the oscilloscope of the engine comprehensive tester to detect the fuel supply interval of each cylinder, it should be carried out after observing the needle valve lift waveform, and the original operation key position should still be maintained.When observing, align the head end of the juxtaposition line on the screen with the zero line of the horizontal scale on the left side of the screen by operating the relevant knob, while the tail end is at about 60° (the camshaft angle of the fuel injection pump) on the horizontal scale on the right side of the screen.Read the number of screen horizontal scales occupied by each line, which is the actual oil supply interval of each cylinder.The lengths of the parallel lines may be unequal, and the camshaft rotation angle occupied by the overlapping area between the shortest parallel line and the longest parallel line is called the fuel injection pump overlap angle, as shown in Figure 2-27.The closer the overlap angle is to zero, the better, that is, the smaller the error of the oil supply interval of each cylinder 2, the better.

Shaft rotation angle, while the oil supply intervals of each cylinder of the 4-cylinder and 8-cylinder diesel engines are 90° respectively.and 45.Camshaft rotation angle, so pay attention to select the horizontal scale when reading.

The oil supply interval of each cylinder can also be expressed by the crankshaft angle.According to the regulations, the error between the actual oil supply interval and the standard oil supply interval should be within the range of ±0.5° crankshaft angle.

If the oil supply interval of each cylinder does not meet the requirements, it can be solved by adjusting the height of the adjustment screw between the fuel injection pump plunger and the roller or replacing the adjustment pads with different thicknesses until it meets the requirements.

Second, the inspection of the technical condition of the injector

The technical condition of the fuel injector determines the fuel injection quality of the diesel engine, so it has a major impact on the combustion process and technical performance of the diesel engine.

The inspection of the technical condition of the injector should be carried out on a special tester, as shown in Figure 2-28.The tester consists of a hand pump, an oil tank and a pressure gauge.The diesel in the fuel tank flows into the oil chamber of the manual oil pump after being filtered. When the manual oil pump is pressed to pump oil, the high-pressure oil flows into the fuel injector through the oil valve, so that the fuel injector sprays oil, and at the same time, the oil pressure is displayed on the pressure gauge. pressure.

1. Test of fuel injection pressure

Remove the lock nut of the tester, unscrew the adjusting screw, and then install the fuel injector on the tester; press the handle of the tester to discharge the air and dirt left in the oil pipe and fuel injector.

Press the handle of the tester at a speed of 60 times per minute, and at the same time observe the reading on the pressure gauge during the injection process of the injector.The fuel injection pressure of the fuel injectors of each cylinder should be the same, and should meet the standard specified by the manufacturer.If the fuel injection pressure of the fuel injector does not meet the requirements, the fuel injection pressure can be adjusted by increasing or decreasing the gasket at the pressure regulating spring of the fuel injector or adjusting the rotation amount of the fuel injector adjusting screw.When the adjusting screw is turned, the injection pressure should increase; otherwise, it should decrease.

After adjusting the injector, tighten the lock nut and perform the fuel injection pressure test again until it is adjusted to meet the standard value.

2. Inspection of spray quality

Press the handle of the tester at a speed of 120 times per minute, and the oil mist sprayed by the injector should be in the form of a fine and uniform mist.The direction of oil beam injection and its cone angle should meet the requirements.For example, the five beams of oil mist from the five-hole injector should have a cone angle of 10°-40°, and they should be uniform and symmetrical; -10.And even and symmetrical, as shown in Figure 60-2.In addition, it is also required that the interior of the oil mist is fine and uniform; the oil injection and oil cut-off are crisp: after multiple injections, the vicinity of the injection hole should be dry or slightly wet, and no oil should appear.

[-]. Oil supply pressure waveform and analysis
The technical condition of the fuel injection pump and injector of the diesel engine determines the injection quality of the fuel, which has a great influence on the working performance of the diesel engine.Without disassembly, the technical condition of the fuel supply system of the diesel engine can be detected through the pressure change in the high-pressure oil pipe during the fuel injection process.When a major part of the fuel supply system works badly, it will inevitably affect the fuel injection process, and its fuel pressure waveform will also change.Therefore, according to the characteristics of the measured fuel injection pressure waveform and comparing it with the standard waveform, the technical status and failure reasons of the fuel supply system can be judged accordingly.

1. Detection of pressure waveform

Diesel engine-specific oscilloscopes, diesel engine comprehensive testers, gasoline and diesel engine comprehensive testers, etc. can detect the pressure waveform in the high-pressure oil pipe of each cylinder and the needle valve lift waveform of the fuel injector without dismantling the diesel engine.Through waveform analysis, not only the maximum pressure Pmax, needle valve opening and closing pressure Po, Pb and residual pressure Pr can be obtained, but also the failure of the fuel injection pump and fuel injector and the uniformity of the fuel injection process of each cylinder can be judged.Commonly used testing instruments include CFC-I diesel engine tester, QFC-4 comprehensive engine tester and WFJ-1 microcomputer engine tester.

During detection, after preheating, self-calibration, and debugging of the detector, install the series-connected oil pressure sensor between the high-pressure oil pipe and the fuel injector according to the use requirements, or clamp the external clamp type oil pressure sensor on the high-pressure oil pipe according to the requirements; Stabilize the engine speed at 800-1000r/min, press the button to select according to the requirements of the instruction manual, and the oil supply pressure waveform of the tested engine will appear on the screen.

The pressure waveform in the high-pressure oil pipe can be observed by selecting four modes of full-cycle single-cylinder wave, multi-cylinder parallel wave, multi-cylinder parallel wave and multi-cylinder overlapping wave by pressing the button.

The full-cycle single-cylinder wave (Figure 2-30) refers to the pressure change waveform in a single-cylinder high-pressure oil pipe when the camshaft of the fuel injection pump rotates 360°.

The multi-cylinder parallel wave (Fig. 2-31) is based on the residual pressure Pr in the high-pressure oil pipe of each cylinder, and the waveform formed by connecting the pressure waveforms of each cylinder from left to right end to end according to the firing sequence. Using this waveform, it can be compared Whether the size of Pq, Pb and Pmax of each cylinder is consistent.

Multi-cylinder parallel wave (Figure 2-32) refers to the waveform formed by aligning the heads of the pressure waveforms of each cylinder and expanding from bottom to top in the vertical direction according to the firing order. By comparing the three-stage area of ​​the pressure waveform of each cylinder, it can be Judging the consistency of the fuel injection volume of each cylinder.

Multi-cylinder overlapping wave (Figure 2-33) refers to the waveform formed by aligning and superimposing the heads of the pressure waveforms of each cylinder. Using the overlapping wave, the height, length, area and Po, ft, Pmax, and pressure waveforms of each cylinder can be compared. Consistency of PR.

When observing the needle valve lift waveform, the oil return pipe of the injector of the measured cylinder should be removed, and the needle valve sensor should be screwed in.When the sensor rod is pushed up, lock the sensor, make the engine run at a medium speed, and press the button to select according to the usage requirements, so that six parallel lines will appear on the screen, and the needle valve lift waveform of the measured cylinder will be displayed on the The screens are correspondingly paralleled on the line (Figure 2-27).When necessary, the lift waveform and pressure waveform of the needle valve of the cylinder can be displayed on the screen at the same time for comparison and observation.

When using the WFJ-1 microcomputer engine tester to test the diesel fuel supply system, in addition to displaying it with an oscilloscope, it can also print out the engine speed, maximum pressure Pmax, residual pressure and pressure waveform.

2. Pressure waveform analysis
(1) Typical fault waveform
(End of this chapter)