Contents: System action ⇊ Catalytic converter ⇊
The EGR system is designed to control nitrogen oxide emissions by recirculating a portion of the exhaust gases into the intake manifold through the EGR valve located on the intake manifold.
On carburetor vehicles, the valve is controlled by a vacuum supplied to it, which ensures that the valve action corresponds to the engine load by the action of the control valves.
The valves open and close very quickly. The incoming air flow through the air ducts maintains the optimal ratio of the gas mixture entering the carburetor, depending on the engine load.
On fuel-injected vehicles, the on-board computer memory contains information about the ideal position of the EGR valve for different engine operating modes. The EGR valve opening degree sensor transmits information to the on-board computer, which in turn uses this information and signals from other sensors to determine the time of sending an electrical pulse to the control solenoid. The solenoid opens the control valve and supplies vacuum to the EGR valve. Both systems include means for limiting the operation of the EGR when the engine is not heated. Since the combustion temperature of the air-fuel mixture is relatively low, the amount of nitrogen oxides formed is significantly lower. In this case, the EGR system is blocked to improve the performance of a cold engine.
System action
For vehicles with fuel injection
The EGR valve does not simply open or close, but changes the degree of opening by the vacuum supplied to the diaphragm valve, which is maximally opened by the action of a vacuum of 200 mm Hg. The on-board computer sets the position of the control solenoid valve, which regulates the opening of the EGR valve according to the programmed program. The action of the control solenoid valve is balanced by a constant volume control valve (CVC valve), ensuring a constant supply of vacuum, and thus ensuring the accuracy of EGR control under various conditions. The air chamber between the control solenoid and the CVC valve acts as an expansion tank, softening the vacuum drops. The control solenoid valve, CVC valve and air chamber are located in the control box on the partition.
Testing
1. First, check that all vacuum hoses and electrical contacts are in good condition. If the engine does not idle, disconnect the vacuum hose to the EGR valve and plug it. If the engine starts at idle, then the problem is in the EGR control system. Start the engine and wait until the fan turns on (the engine is warm). Disconnect the vacuum hose to the EGR valve and connect a hand pump with a pressure gauge to the hose and to the valve.
2. With the engine idling, apply vacuum to the EGR valve. The engine should stop and the valve should hold vacuum! If not, replace the EGR valve.
3. Connect a hand pump with a pressure gauge to the vacuum hose from the control solenoid valve and restart the engine at idle speed. No vacuum should be detected.
4. If vacuum is detected at the EGR valve when the engine is idling, check the wires to the control solenoid valve. One of the wires should have 12V at any time during engine operation. The ground wire goes to the on-board computer, which controls the opening of the solenoid valve, monitoring the main circulation. Turn off the ignition and, using a digital ohmmeter, check the wire between the computer and the solenoid valve: is it shorted? If the wire is OK, then either the on-board computer is receiving an incorrect signal from the sensor, or the computer itself is faulty.
5. The vacuum going to the control solenoid valve should be about 200 mmHg when the engine is idling. Connect a pump with a pressure gauge to the hose coming from the air box. If the pressure gauge does not read as specified, check the vacuum at the outlet of the CVC valve. Full manifold vacuum should be determined at the inlet of the CVC valve. If the air box or CVC valve is leaking pressure or not functioning properly, it cannot be repaired.
6. To check the EGR valve opening degree sensor, turn off the ignition and disconnect the wires to the EGR valve. Then turn on the ignition and check if there is 5V at the sensor terminals. Turn off the ignition, connect an ohmmeter to the central and any end terminal of the sensor and change the pressure to the EGR valve with a hand pump. The resistance should change as the valve opens and closes.
Carburetor engines
The system is controlled by a pair of control valves that are actuated by changes in system vacuum. A change in throttle vacuum opens valve A, which allows manifold vacuum to open valve B. As valve B opens, some of the vacuum is released into the carburetor passages, causing valve A to close and the EGR valve to open. Ultimately, a balance is achieved by the interaction of manifold and transmit vacuum. This links the opening of the EGR valve to the opening of the throttle valve and therefore to engine load. When the engine is cold or the vehicle is not moving, the evaporative emission control solenoid shuts off the vacuum to valve B, preventing it from reaching the EGR valve. The system is much easier to test than it is to understand. With the exception of the solenoid, the system is entirely mechanical. All faults are related in some way to a leaking or clogged vacuum hose, or a faulty EGR valve.
Testing
1. With the engine cold, connect a pressure gauge to the EGR valve vacuum hose and run the engine at 3000 rpm. No vacuum should be detected. If vacuum is detected, check the cleaning control system. Start the engine at idle, let it warm up to optimum temperature (until the radiator fan turns on) and open the control box on the bulkhead.
2. Remove the upper vacuum hose from the shut-off solenoid valve and the valve cover. Check the vacuum in the hose to the EGR valve under the following conditions: at idle (no vacuum);
- in the engine shaft rotation mode of 3000 rpm (vacuum 51-152 mm Hg);
- in the engine shaft rotation mode of 3000 rpm with the ventilation hose number 11 blocked. (vacuum less than 51 mm Hg);
- reset the speed (there should be no vacuum).
3. To test the EGR valve, plug the vacuum hose and attach a hand pump to the valve. Create a vacuum of about 150 mm Hg with the engine idling. The engine should stall and the vacuum should hold, indicating that the diaphragm is intact. If the engine does not stall, either the valve is not opening or there is an obstruction in the vacuum supply system.
Catalytic converter
The most visible part of the emission control system is the catalytic converter. Its function is to combine unburned hydrocarbons and carbon monoxide (HC and CO) with oxygen to produce carbon dioxide. It also binds nitrogen oxides. The catalytic converter operates in a very narrow range of air-fuel mixture concentrations. The oxygen sensor in the exhaust system transmits information about the O ₂ concentration in the form of electrical voltage to the on-board computer, which constantly adjusts the ratio of fuel and air in the air-fuel mixture to ensure the optimal composition of the gas mixture supplied to the catalytic converter. It should be noted that this process is carried out both on carburetor engines and on engines with fuel injection. The oxygen sensor is the main element of feedback with the carburetor or control computer.
This is a completely passive device, there are no actuators or sensors. Contrary to popular belief in the late 70s, the device does not affect engine operation until the catalytic converter melts and causes high exhaust gas resistance. If this is suspected, the catalytic converter can be removed and inspected. A simple look inside will assess the integrity of the honeycomb in the ceramic blocks. If some of them have melted and can cause exhaust gas resistance, this will be clearly visible. On some cars, the catalytic converter is mounted directly on the exhaust manifold, on others - further in the exhaust system, but always before the muffler.
The only condition that must be met for the normal operation of the catalyst is the use of unleaded gasoline. It is not adapted to the action of additives in leaded gasoline and will quickly lose its properties. All Honda engines are adapted for operation with unleaded gasoline; they do not require fuel with leaded additives to increase the octane number. The quality of gasoline is achieved by advanced oil distillation technology.
