Automobile Inspection Technology

Chapter 9 Automotive Engine Detection (5)
Comparing the measured pressure waveform with the typical fuel supply pressure waveform, it can be judged that the fuel injection pump or fuel injector is faulty. The common fault waveforms measured by the WFJ-1 microcomputer engine tester are as follows:
①The fuel injection pump does not pump oil or the fuel injector is "bitten" in the open position and cannot be closed: When the plunger spring of the fuel injection pump is broken or the fuel injection pump does not pump oil or the pump oil is very little due to other reasons, the high-pressure fuel pipe cannot A sufficiently high fuel injection pressure is established, and the fault waveform at this time is shown in Figure 2-34.

② The fuel injector cannot be opened in the closed position: the main reason for this failure is that the opening pressure of the needle valve is adjusted too high or the needle valve of the fuel injector is "bitten" by high temperature ablation.At this time, the fuel injection pump supplies fuel normally but the fuel injector does not inject fuel, which is reflected in the oil pressure waveform curve, and the curve is smooth without jitter, as shown in Figure 2-35.

Figure 2-35 The fuel injector cannot be opened in the closed position Figure 2-36 The fuel injector drips before spraying

③Pre-injection drip of the fuel injector: The main reason for the pre-injection drip is that the needle valve of the fuel injector is not tightly sealed, or the needle valve is excessively worn, or dirt sticks to the sealing surface of the needle valve.On the oil pressure waveform curve, it shows that there are two jitter points in the stage of pressure rise, as shown in Figure 2-36.

④ High-pressure oil circuit is not tightly sealed: When the high-pressure oil circuit is not tightly sealed, the residual pressure part of the oil pressure waveform curve vibrates in a narrow range and gradually decreases, as shown in Figure 2-37.

⑤ Injection every other time of the fuel injector: every other time after a certain injection, the residual pressure in the oil pipe is low, and a primary oil supply is very small, and the oil pressure generated in the high-pressure oil pipe is not enough to open the needle valve of the fuel injector. So the fuel is stored in the oil pipe, and the needle valve is not opened until the secondary fuel supply, so that the two primary fuel supplies are sprayed out once.Secondary injections generally occur when the fuel delivery is small and the injector spring pressure is high.Reflected on the oil pressure waveform curve, the residual pressure will vibrate up and down, as shown in Figure 2-38.

(2) Oil pressure detection

In order to make the diesel engine have good working performance, the maximum pressure Pmax observed on the oil pressure waveform curve of each cylinder of the engine, the needle valve opening pressure PQ, the needle valve closing pressure Pb and the residual pressure h in the oil pipe should be basically equal, and Meet the specified requirements.Table 2-5 lists the injector injection pressure (cracking pressure of injector needle valve) of common models.If the fuel injection pressure is lower than the specified value, the fuel injector should be debugged on the special fuel injector test bench.

(3) Consistency detection of fuel supply of each cylinder

On the premise that the pressures P0Pb, Pnax and Z of each cylinder are basically the same, the consistency of the fuel supply of each cylinder can be detected by waveform comparison.When comparing waveforms, first adjust the engine speed to medium and high speeds, and then use parallel waves or overlapping waves to compare the oil levels of each cylinder.
The consistency of the pressure waveform.If the overlap of the three phases of the waveform is good, it means that the fuel supply of each cylinder is relatively consistent; if the waveform of a certain cylinder is narrow, it means that the fuel supply of this cylinder is small; if the waveform is wide, it means that the fuel supply of this cylinder is large.

The start-up fuel supply of a diesel engine is often equal to or greater than the rated fuel supply.When checking the start-up fuel supply, step on the accelerator pedal to the bottom, at this time, the control arm of the fuel injection pump leans against the high-speed limit screw, and then observe or measure whether the fuel supply rod can be in the extreme position of the fuel supply direction.Otherwise, adjustments should be made.However, if the starting fuel supply is adjusted too much, it will also cause difficulty in starting the diesel engine.

(4) Needle valve lift waveform
The observation of the lift waveform of the needle valve can make a correct judgment on the opening and closing time of the needle valve, the jumping of the needle valve and the abnormal injection phenomenon. The non-injection, needle valve vibration, etc. will be reflected in the needle valve lift waveform.Among them, alternate injection or non-injection occurs more frequently at idle speed or low speed when the fuel injection quantity is small.At this time, both the peak value of the pressure waveform Prnax and the residual pressure Pr change, and the lift waveform of the needle valve is sometimes absent or the lift is sometimes large and sometimes small.

(Section [-]) Detection and Analysis of Engine Lubrication Quality
During the operation of the car, the main problems of the lubrication system are abnormal phenomena such as changes in lubricating oil pressure, deterioration of lubricating oil, or excessive increase in lubricating oil consumption.This is not only related to the technical status of the lubrication system itself, but also related to the crank connecting rod mechanism and the gas distribution mechanism.Therefore, the detection of lubricating oil pressure, lubricating oil deterioration degree and lubricating oil consumption can not only characterize the technical status of the lubrication system, but also directly or indirectly explain the technical status of other related matching pairs.

[-]. Detection of oil pressure and oil consumption

1. Oil pressure detection

The oil pressure of the engine lubrication system firstly depends on the technical condition of the lubrication system, such as the performance of the oil pump, the adjustment of the pressure limiting valve, the resistance of the oil channel and the oil filter, etc.; at the same time, the oil pressure is also related to the quality of the oil, the temperature of the oil Viscosity is related. If the oil viscosity is low and the temperature is high, the oil pressure will decrease; otherwise, the oil pressure will increase.In addition, the oil pressure is also related to the clearance of the crankshaft main bearing, connecting rod bearing and camshaft bearing. When the clearance of the bearings increases after wear, the oil leakage at the bearing clearance will increase and the oil pressure will drop. Therefore, the oil pressure is often used as a diagnosis Important parameter in relation to bearing clearance.If the technical condition of the oil pump is normal, the reduction in oil pressure is mainly caused by excessive wear of the crankshaft main journal and connecting rod journal.Experiments have shown that when the crankshaft main bearing clearance increases by 0.01mm, the oil pressure will decrease by about 0.01MPa.

The oil pressure value of the lubrication system can be displayed on the oil pressure gauge on the car dashboard, but since the oil pressure gauge and oil pressure sensor cannot guarantee the necessary measurement accuracy, a special inspection oil pressure gauge should be used during regular inspections.When testing, first remove the oil pressure sensor on the lubricating oil channel of the engine, and install the oil pressure gauge; then start the engine to run at the specified speed, and the indicated value on the oil pressure gauge is the oil pressure of the lubrication system.

2. Oil consumption detection

There are many factors that affect the oil consumption. Leakage of the lubrication system, abnormal operation of the air compressor, improper selection of oil specifications, and wear of the cylinder piston group will all affect the oil consumption.Therefore, the oil consumption can not only reflect the engine lubrication system technical
In addition to technical conditions, it can also be used to judge the wear of the engine cylinder piston group.Because when the brand of engine oil used is correct and other mechanisms reflect normal conditions, excessive wear of the cylinder piston group, increased clearance, and engine oil leakage into the combustion chamber are the main causes of oil consumption.

important reason for the increase.

When the car is in normal use, the engine oil consumption is not large.For an engine with little wear and normal operation, the oil consumption is about 1-0.5L/100km; when the engine is severely worn, it can reach 1L/100km or more.

To measure the oil consumption, it is only necessary to convert the actual oil consumption (L) of the car after a certain mileage (1000-1500km) into the average oil consumption per 100 kilometers of the car (L/[-]km).

Second, the detection method of engine lubricating oil quality

1. Physical and chemical performance index detection method
Regularly sample and test the lubricating oil in use to detect the changes of its physical and chemical performance indicators compared with the new engine oil of the same brand, which can quantitatively evaluate the change degree of lubricating oil quality.For example: the detection of viscosity changes can reflect the degree of pollution, oxidation or fuel dilution of engine oil; the detection of acid value changes can reflect the degree of oxidation of lubricating oil; The content of ether insoluble matter, n-pentane insoluble matter and benzene insoluble matter can reflect the degree of pollution of lubricating oil by fuel carbon, highly cracked matter, metal particles, corrosion products and external impurities; the detection of water content can reflect the degree of contamination of lubricating oil The degree of emulsification; detecting the content of metal particles, especially the iron content, can not only reflect the degree of contamination of the lubricating oil, but also reflect the wear rate and degree of wear of the relevant parts of the engine.

The oil change index of gasoline and diesel engine lubricating oil in my country is based on the change degree of physical and chemical performance indexes.

The oil sample should be obtained from the main oil passage of the lubrication system when the engine is running at idle in a hot state.When it is impossible to take samples in the main oil channel, samples can be taken from the oil drain hole of the oil pool 5 minutes after the engine is turned off.Do not add new oil to the oil pool before sampling.The quantity of each sample is subject to availability.The sampling container should be clean and free from water and impurities.

2. Filter paper spot analysis

Put a drop of in-use lubricating oil on the special filter paper according to the specified conditions, and the oil drop gradually infiltrates and spreads around.Due to the difference in the number and particle size of impurities contained in the lubricating oil, the residual cleansing and dispersing ability is different, so the degree of diffusion is also different, so multi-circle ring-shaped spots with different colors and shades are formed on the filter paper.Comparing and analyzing the titrated speckle pattern with the standard speckle pattern can become a simple and fast method for on-site analysis of engine oil quality.This method can characterize the remaining cleanness, dispersibility and aging deterioration degree of the lubricating oil in use, and can be used as the basis for replacing a new lubricating oil when there is no complete set of physical and chemical performance index testing methods.

(1) Morphology of filter paper spot pattern

On the spot diagram of lubricating oil titrated, it can generally spread into three annular spots, which are called deposition ring, diffusion ring and oil ring, as shown in Figure 2-39.

The deposition ring is in the center of the spot diagram, which is the deposition area of ​​coarse particles in the lubricating oil.The degree of contamination of the lubricating oil can be roughly judged from the depth of its color. The ring of the diffusion ring on the periphery of the deposition ring is the trace left when the fine particle impurities suspended in the lubricating oil diffuse outward.The finer the impurity particles, the farther they diffuse, and the lighter the color.The width of the diffusion ring and the uniformity of the color indicate the degree of dispersion of contamination impurities in the lubricating oil, that is, the detergency and dispersibility of the lubricating oil or the consumption degree of the detergency and dispersant.The color of the oil ring on the periphery of the diffusion ring ranges from light yellow to brownish red, indicating the degree of oxidation of the lubricating oil.

The quality of lubricating oil in use can be judged by comparing and analyzing the titrated filter paper speckle pattern with the standard filter paper speckle pattern.

(2) Filter paper spot diagram and comparative analysis
The standard filter paper speckle pattern is divided into six levels.The characteristics and analysis and judgment methods of each level of spot diagram are as follows.

①The core area and diffusion ring of the primary filter paper spot pattern are bright and colorless or very light in color, and there is no obvious sedimentation ring.It shows that the new lubricating oil or the lubricating oil that has been used for a short time has no pollution and can be used continuously.

②Sedimentary ring and diffusion ring in the second-stage filter paper speckle pattern are clearly demarcated, the diffusion ring is wide, and the oil ring is bright.It shows that the lubricating oil has not been used for a long time, the degree of pollution is very light, the cleaning and dispersibility is good, and it can continue to be used.

③Third grade filter paper spot pattern shows dark sedimentary ring, wide diffusion ring and bright oil ring.It shows that the lubricating oil has been used for a long time and the degree of pollution is relatively heavy, but its cleansing and dispersibility is still good, so it can continue to be used.

④ The spot pattern of the fourth-grade filter paper shows that the deposition ring is dark, the diffusion ring begins to shrink, and the oil ring is light yellow.It shows that the lubricating oil has been used for a long time, the pollution is serious, the deposits have increased, and the cleaning and dispersibility has decreased, so it can still be used continuously.

⑤ The spot pattern of the fifth-grade filter paper shows that the sedimentary ring is dark black, even sludge-like, not easy to dry, the diffusion ring is narrow, and the oil ring is enlarged and yellow.It shows that the pollution of the lubricating oil is very serious, the detergency and dispersibility of the lubricating oil are very poor, and the detergency and dispersant are almost exhausted, so it cannot be used any more, and new engine oil must be replaced.

⑥ In the six-stage filter paper spot pattern, only the extremely black sedimentary ring and brown oil ring remain, and the diffusion ring has completely disappeared.It shows that the pollution of the lubricating oil is very serious, the polluted impurities are completely condensed in the deposition ring, the detergent and dispersant is exhausted, and the detergent and dispersibility disappears. The oil change period has already passed, and the lubricating oil should be replaced in time.

The filter paper spot analysis method is relatively simple and fast, suitable for on-site operations, and can give people an intuitive impression.However, it can only roughly analyze the quality of lubricating oil in use, and cannot achieve quantitative analysis.

3. Lubricating oil detergency analysis method
Oxidation products formed after lubricating oil aging can be mixed with mechanical impurities such as metal particles produced by machine parts wear, and form sludge deposits in lubricating oil.This kind of sludge deposits, when the amount is small, is suspended in the engine oil, and when the amount is large, it will be precipitated from the lubricating oil, causing the blockage of the oil passage and the oil filter, affecting the supply of lubricating oil, and even forming carbon deposits in the piston ring groove, reducing the wear of the piston ring. activity.For this reason, an oil-soluble multi-effect detergent and dispersant can be added to the lubricating oil to make the lubricating oil have detergent and dispersibility.The lubricating oil with clean and dispersive properties has the ability to disperse, loosen, and remove harmful substances such as carbon deposits and dirt from the surface of the internal parts of the engine, so that they will not deposit, thereby keeping the surface of the parts clean and bright.

The detergency of lubricating oil can be obtained by regularly monitoring the pollution status of lubricating oil and the consumption of detergent and dispersant by using an oil detergency analyzer to judge the degree of deterioration of lubricating oil.The detergency and dispersibility coefficient K value of the engine oil is used to indicate that the lubricating oil has different detergency and dispersibility or pollution degrees.

The variation range of the detergency dispersibility coefficient K of engine oil is 0-1.When K=0, the detergency and dispersibility of lubricating oil is equal to zero; the detergency and dispersibility of lubricating oil is the best.

4. Dielectric constant analysis method

The dielectric constant of a substance (also called permittivity) is the ratio of the capacitance when a certain substance is used as an electrolyte in the same capacitor to the capacitance when it is a vacuum.The dielectric constant usually changes with temperature and the frequency of electromagnetic waves propagating in the medium, and the dielectric constant of lubricating oil also has this property.At the same temperature, the change in the dielectric constant of the lubricating oil in use relative to the new lubricating oil of the same brand is mainly caused by the gradual decrease of additives in the lubricating oil and the gradual increase of pollution and aging.By measuring the change in dielectric constant, the degree of deterioration of lubricating oil can be analyzed.When there are metal particles and highly conductive compounds in the measured lubricating oil, it will have a great influence on the measured value.

The appearance of the RZJ-2A lubricating oil quality computer detector (referred to as the oil quality meter) is shown in Figure 2-40.The instrument uses a planar capacitor with high sensitivity to pollutants as a sensor. This planar capacitor is composed of two spiral metal leads, winding from the outer edge to the center.The lubricating oil under test acts as a capacitor dielectric.The electrical signal obtained from the sensor is converted into a digital signal through a dedicated digital circuit, sent to a computer for processing and compared with a reference signal.When the digital display shows zero, it means that the measured digital signal is equal to the reference signal; when the digital display is not zero, the measured digital signal is greater than or smaller than the value of the reference signal, indicating the change in the dielectric constant of the oil.The greater the change, the more serious the pollution, aging and deterioration of lubricating oil.

The instrument is easy to carry, simple to operate, and can realize rapid detection.When using the instrument, clean the sensor oil tank thoroughly with absorbent cotton first, and then put 3-5 drops of new engine oil of the same brand as the lubricating oil to be tested into the sensor oil tank to make the lubricating oil flush with the edge of the oil tank. After 2-58, the lubricating oil has diffused in the oil tank. Press the "Reset" button lightly, and it will be reset after about 28, and "±0.00" will be displayed.Thoroughly clean the sensor oil tank, put 3-5 drops of the measured lubricating oil sample in the sensor oil tank, press the "Measure" button lightly, and the digital display will immediately show the change in the dielectric constant of the measured oil sample relative to the new lubricating oil value.Whether the tested lubricating oil needs to be replaced with new oil can refer to relevant standards.When the dielectric constant change value measured by the instrument reaches the specified range, the engine should be replaced with new lubricating oil.

After obtaining the reading from the digital display, you should continue to observe the changes in the numbers in the display to find out the reason for the deterioration of the lubricating oil.The numbers in the display screen change in the following three situations:
①The number is "+", which is stable, indicating that the lubricating oil is generally polluted and deteriorated due to aging, that is, the lubricating oil contains oxides, sludge, dirt, carbon and acidic substances, etc.

②The number drifts sharply in the direction of "+", indicating that there are more water, antifreeze and large metal particles in the lubricating oil.

③The number drifts toward "one", indicating that the lubricating oil is diluted by gasoline.But when lubricating oil is diluted with diesel oil, the number does not drift toward "one".It can be seen that the dielectric constant analysis method can not only monitor the deterioration degree of lubricating oil to determine the timing of lubricating oil change, but also analyze the cause of lubricating oil deterioration.

5. Spectral analysis

When the engine is working, due to the cleaning effect of the lubricating oil, the wear particles on the friction surfaces are brought into the oil pool and suspended in the lubricating oil.These wear particles are mainly iron, chromium, copper, tin, lead, aluminum, silicon, etc., and their content in lubricating oil is often a function of machine wear.Therefore, monitoring the content of metal particles in lubricating oil can not only show the degree of contamination of lubricating oil by mechanical impurities, but also can be used to determine the degree of mechanical wear.At the same time, the change rate of the metal particle content in the lubricating oil can also reflect the wear rate of the machine parts.Therefore, this detection work can be carried out regularly to characterize the technical condition of the engine.

The light band formed by the monochromatic light decomposed into monochromatic light after passing through the prism or grating is called the spectrum.Each element has its own unique spectrum.Analyzing lubricating oil in use by spectroscopic method can determine the composition and content of metal particles in the lubricating oil, and can realize the diagnosis of the engine without disassembly.

When the iron content in the lubricating oil is too high, it can be diagnosed that the cylinder and piston ring are severely worn.Secondly, when the journals of the crankshaft and the camshaft and the tappet and the cam matching pair wear, the iron content in the lubricating oil can also increase.If the cylinder liner is chrome-plated or the piston ring is chrome-plated, when the chromium content in the lubricating oil increases, it also indicates the wear of the cylinder and piston ring, but the chromium content is much smaller than the iron content.Piston wear increases the aluminum content in the lubricating oil.Use lubricating oil containing lead. When the leakage gas of the cylinder increases or the diaphragm of the mechanical oil pump leaks, the lubricating oil is not only diluted, but also the lead content increases.The sliding bearings used in engine crankshafts and camshafts are mostly tin-based, lead-based, copper-based or aluminum-based anti-friction alloys. The material formulation of the engine bearings can be used to diagnose the wear of the plain bearings.

(End of this chapter)