At present, professional level of repair work is becoming higher and higher, and electronic control system and engine configuration are becoming more complicated, industry has proposed a new method for detecting indestructibility of engine, i.e. , try not to disassemble motor and related components, but first determine fault point that causes problem, in order to achieve higher accuracy. Correct original directional (empirical analysis) analysis, move to a quantitative (based on results of test data) analysis;
In fact, in our actual maintenance operations, what we most feel is need to use directional analysis to determine direction. Quantitative analysis to test reasoning is fastest, simplest, ideal, and practical method. This requires that we have a whole set of organized, practical, and regular methods for discovering when we encounter problems in real work. I combine my practical experience with training from specialists in auto repair industry;
The conclusion can be summarized as follows: (Checking here is done after a visual inspection, for example: some original parts may be clearly different in appearance (original product), wire harness connector is not correctly inserted, and appearance does not match assembly Separate component instance, causing problem.
Actually, I understand that troubleshooting electronically controlled engines means that troubleshooting should also follow:
1. Oil (fuel system)
Second, electricity (electronic control system)
Third, air (intake and exhaust system)
Fourth, mechanical (mechanical system)
Complex analysis can be divided into:
1. Fault code analysis. (If fault indicator is on, it is recommended to perform a code reading analysis first)
Secondly, data flow analysis. (Based on state of car, observe whether dynamic changes in sensors and actuators correspond to standard data)
Thirdly, oil pressure analysis. (Should be used when fault is related to fuel system)
Fourth, ignition analysis. (Check ignition coil, distributor, high voltage wire and ignition waveform, etc.) Mainly check by replacement.
5. Exhaust gas analysis. (Analyze relationship between exhaust gas data value and malfunction phenomenon)
6. Pressure/vacuum analysis. (Normal value 57-71 kPa, idle fluctuation should not exceed 5 kPa)
Seven, temperature analysis. (To check relationship between malfunction phenomenon and temperature, such as temperature difference between exhaust cylinders is not more than 100 degrees, water temperature sensor, sensor, air conditioning system and temperature difference between intake and exhaust three-way catalytic converter, etc., everything related to temperature)
8. Analysis of electrical control circuits and computers. (Use multimeter, simulator and simulate online signals to observe changes before and after comparison, and use oscilloscope to check signal change relationship between each sensor and computer)
9. The simplest scheduled engine inspection includes:
1. Check ignition timing. (chronometer, vacuum gauge for checking analysis)
2. Check idle speed (corresponds to original factory setting)
3. Check pressure in cylinder (is pressure difference in each cylinder constant)
4. The rate of air leakage from cylinder can be analyzed by correlation method in combination with a vacuum gauge)
5. Gas distribution phase (can be checked with a vacuum gauge)
6. Exhaust gas back pressure (generally, idle speed does not exceed 13.8 kPa, which can be analyzed by vacuum gauge correlation)
7. Checkmatch spark plug, distributor and cylinder line to specified data)
8. Check oil pressure (especially with extraneous noise)
10. Test analysis of oxygen balance (for EOBD system)
This is a stage of comprehensive analysis and diagnostics of engine, and waveform analysis is only one of methods, this is confirmation and verification of maintenance, when repairs are carried out at a deeper level
Maintenance experience and experience
Common engine check methods include
1. Check ignition timing (Check initial ignition timing)
How to check:
1. For electronically controlled engines, you need to give computer a signal to check ignition timing. For example, for Toyota cars, short E1 and TE1 at engine detection and diagnostic site, for Mitsubishi 4G64 engines, short brown circle next to engine. Close connector so ECU knows to check initial ignition timing. For 491 series engines with electronic control, ignition timing that performs initial detection The function can be used to set a fixed value, purpose of this is to allow computer to override ignition timing Timely adjustment so that ignition timing is fixed in its original (fixed) position.
2. Use timing gun to determine if ignition timing is at specified position (the value on computer display should correspond to advance angle of timing mark on engine pulley as seen by timing gun;< /p>
3. Consistency of test results indicates that this is normal, a discrepancy indicates that there is a basic misadjustment or mechanical damage (for example, pulley key of crankshaft pulley of 491-ME series can be detected by this method). ), incorrect parts are installed (the crankshaft pulley is incorrectly installed).
Second, check idle speed (normal engine operation is inseparable from stable and standard idle speed). Idle speed reflects problems of many aspects of engine;
How to check:
1. Adjustable type (700±50rpm) is mainly adjusted by screws, and needs to be adjusted according to original factory maintenance manual, such as 2RZ-E motor,
2. Non-adjustable (700±50 rpm) - set value of computer program, there is no artificial adjustment here.
3. The idle speed is unstable and ignition timing must be correct while driving.
4. Idle reaction ①.Is oil pressure normal;
② whether fuel injection is normal;
③, ignition timing early, late
Thirdly, determination of vacuum level (the degree of vacuum is one of most direct, efficient and reliable data that reflects quality of engine);
Test Method: Use a vacuum gauge to check vacuum value in engine intake manifold
1. Connect a vacuum gauge behind throttle, start engine under normal conditions and readvacuum value.
2. Check change in vacuum degree by changing throttle opening as desired,
3. Application point of vacuum gauge;
①, It can accurately detect weak closing caused by valve damage (poor valve sealing, rocker shaft sticking)
②. You can more accurately judge early or late ignition;
③, You can see timing of valve timing, (for 4G22/20) series can check valve timing (generally 21 inchesHg; 17-19, there is a problem - intake and exhaust camshaft sprocket and shaft assembly is not up to standard, and there is a phenomenon of relative displacement)
Fourth, test, spark plug, high voltage wire, distributor, distributor, high voltage wire resistance value
1. Each model must choose a spark plug that is suitable for that model. Cold type spark plugs are suitable for powerful engines with a high compression ratio; (Jinbei cannot use multi-pole spark plugs, Jinbei's single-point installation of wrong spark plugs will damage computer, Mitsubishi 4G64\63 engines cannot be equipped with BOSH spark plugs) Otherwise, it will cause throttle to quickly burn out and cut off. Car waiting for unexpected failures . That is, spark plugs must not be mixed, otherwise they will damage components such as video computers and ignition modules.
2. Check spark plug gap (electronic ignition spark plug gap is 1.2mm), burning color, pay attention to selection of cold and hot spark plugs, and measure cylinder line resistance (experience: EFI Jinbei single point cylinder line resistance value is less than 8 kΩ, you can continue to use);
3. Check distributor, distributor cap for severe ablation or leakage, water ingress, dirt, incorrect sensor gap, wear loosening of distributor shaft, resulting in vibration and poor acceleration. The method is mainly dependent on observation. ; A bad sensor signal coil leads to uneven flameout. When engine is idling, use a tool to tap distributor body gently to make it vibrate, observe and compare before and after condition, and most of them can be checked.
5. Analysis of ignition waveform (using a dedicated oscilloscope ignition tool)
1. Using an oscilloscope, check engine ignition system. The purpose of inspection is to observe state of combustion in engine cylinder, find and analyze problems;
2. It can test primary, secondary and ignition signals, and perform parallel ignition signals (analysis and comparison of two cylinders), display signals (comparison of four cylinders) to check working conditionsfrom combustion
3. The ignition waveform can test ignition coil, high voltage line, spark plug, cylinder pressure, gas mixture concentration and lean, and high voltage leakage waveform will be low;
The above inspections are more accurate and faster without dismantling parts, however they require a higher level of inspection and maintenance personnel.
6. The pressure in cylinder, whether it is normal or not, is first condition for normal operation of engine;
How to check:
1. Use pressure gauge in cylinder to check. The cylinder pressure of EFI vehicles is usually above 10; 491 is usually 11–12 kg
2. To locate a fault with insufficient cylinder pressure: Inject some oil into piston cylinder bore to check if it is a valve or a piston ring.
Seventh, determine valve timing: (use crank angle to indicate opening, closing and duration of proximal and exhaust valves, which is called valve timing.) It represents intake valve and exhaust valve and relative position crankshaft)
1. Manufacturing defects of valve mechanism parts or insufficient grinding accuracy;
2. Wear or deformation during use,
3. Incorrect assembly and adjustment
4. The gear train of crankshaft and camshaft (two positions of camshaft of double camshaft model itself) is not correct due to improper assembly and maintenance. For example: timing requirements for 4G22/20 series engines are very strict
Eight, cylinder air leakage rate (might explain problem more accurately than checking cylinder pressure)
How to check:
Shift into forward gear and apply handbrake, apply compressed air through spark plug hole, listen for sound of air leaking from exhaust pipe and oil pan, and connect a pressure gauge to check for air leakage.
This method is rarely used and is only used when checking a specific engine cylinder, for example, valve closing is not strict. In cylinder being measured, valve must be fully closed and piston is at top dead center.
9. Exhaust gas backpressure (to determine exhaust gas pressure in exhaust pipe) use special tools, application time: when all of above checks are normal, when there is a bad landing and when acceleration is weak.
Remove oxygen sensor → install an exhaust back pressure gauge. 2000 rpm: exhaust backpressure (15 kPa)
Cause: Three-way catalytic converter or muffler may be blocked.
(1), A Connect a vacuum gauge to intake manifold and start engine at a high speed of 3000 rpm
B slow down quickly
C is not locked, vacuum gauge will rapidly increase when throttle is closed and then lock at normal value
Locked, vacuum gauge needle does not show vacuum increase.
(2), A Install a fuel pressure gauge (replace exhaust back pressure gauge) on exhaust pipe oxygen sensor port
B Normal idle speed does not exceed 13.8 kPa and back pressure does not exceed 20.6 kPa at 2000 rpm, about 0.2 kg/cm2
10. Exhaust gas analysis (use an exhaust gas analyzer to check exhaust emissions)
CO value: high gas mixture is too rich, you can analyze color of carbon deposits on spark plug,
HC value: high misfires (high voltage) intake and exhaust valves not closed tightly CO↓HC↑ typical mixture too lean (no combustion);
NOx value: high content of nitrogen and hydrogen compounds, good combustion and three-way catalysis, EGR valve (reuse of exhaust gases to reduce combustion temperature)
White smoke: too high moisture content in exhaust gases. A possible reason is a damaged cylinder head gasket or water in exhaust pipe (a newly repaired cylinder head gasket is broken and boiling water) you need to run car for a while before testing.
Blue smoke: Cause engine oil is burning and piston ring is not tight. To distinguish, use a cylinder pressure test; The second time I started car, at moment car was started, there was apuffy smoke. this time it may happen that oil has leaked out of valve guide; spark plug can be taken apart and inspected to tell them apart;
Alternative application of residual gas analysis:
When there is abnormal coolant leakage and cylinder gasket damage, fault location can be checked by determining HC value at water inlet to water tank; check HC value on water tank; experience: car is usually not more than 100 ppm; if detected HC value exceeds 200 ppm, this means that gasoline mixture has entered water tank, and damage to cylinder gasket and related parts can be judged. I hope everyone will make good use of this engine detection method, it will bring you great convenience.