Contents: Checking the valves ⇓ Replacing valves ⇓
Turbocharged and fuel-injected engines are equipped with exhaust gas toxicity reduction systems, which, in principle of operation and purpose, are similar to those described in Section. 8 "Emission control system", however, due to certain design differences, the testing and maintenance procedures for this system are somewhat different and require separate consideration.
When troubleshooting the exhaust gas toxicity reduction system, you should also check the fuel supply and exhaust systems, as well as the electrical components, as they are interconnected.
The air injection system consists of a control valve and a reed valve, which are installed on the air filter housing. Turbocharged engines, in addition to the valve on the air filter housing, have additional remote reed valves mounted on the right shock absorber cup.
Figure 15.50. Air injection system diagram: a – non-turbocharged engines; b – turbocharged engines; 1, 4 – control valves; 2, 3, 5 – reed valves
When the vacuum in the intake manifold reaches a certain level, the control valve opens and fresh air is sucked into the manifold due to a sharp increase in the exhaust gas flow rate (figure 15.50). This ensures the afterburning of unburned fuel residues and reduces the hydrocarbon content in the exhaust gases. The two remote valves in turbocharged vehicles only operate when there is a strong enough exhaust flow to draw air through these valves (typically at an engine speed of 2500 min⁻¹).
Checking the valves
To check the air injection system, remove the air cleaner cover and idle the engine. A noticeable flow of air should be sucked into the air duct, which is checked using a piece of paper held up to the hole.
Increase the engine speed to 2500 min⁻¹ and make sure there is no air intake. Visually check that exhaust gases do not escape through the opening.
If the system does not operate properly, check the air check valve and reed valve.
To check the air check valve, remove it from the housing and connect it to a vacuum pump. Gradually bleed the air and observe the stem, which should extend at a vacuum of 180–280 mmHg. If the valve fails the test or is leaking, replace it.
To check the reed valve, warm up the engine and set it to idle mode. Connect a vacuum pump and pump out air to a pressure of 500 mmHg. Lift the air filter cover and check if air is being sucked into the hole. Increase the engine speed to 2500 min⁻¹ and check for exhaust gases. If the valve fails the test, replace it.
To test remote reed valves (for turbocharged engines only) increase the engine speed to 2500 min⁻¹ and check the air intake into the channels. Make sure there is no exhaust leak. If both valves fail the test, replace them.
Replacing valves
Figure 15.51. Control valve fastening elements
To replace the check valve, unscrew the two screws and remove the valve from the air filter housing (figure 15.51). Installation is carried out in the reverse order of removal.
Figure 15.52. Reed valve fastening elements: 1 – gasket; 2 – mounting plate; 3 – rubber insert; 4 – reed valve; 5 – body
To replace the reed valve, remove the air cleaner cover. Remove the mounting plate, rubber insert, gasket and reed valve from the filter housing (figure 15.52). Check the condition of the insert; if there are cracks or other signs of damage, replace the insert. Installation is carried out in the reverse order of removal. Be sure to replace the gasket.
Figure 15.53. Fastening elements of remote reed valves: 1 – back cover; 2, 4 – gaskets; 3 – distribution plate; 5 – guide tube; 6 – body; 7 – air filter; 8 – rubber insert; 9 – reed valve; 10 – front cover
For replacing remote reed valves (for turbocharged engines only) remove the valve body from the right shock absorber cup and place it on a clean surface. Remove the four screws at the corners of the cover and remove the valve parts (figure 15.53). During assembly, replace the gaskets and, if necessary, the rubber inserts.