The Exhaust Gas Recirculation (EGR) system is designed reintroduce exhaust gas into the combustion cycle, thereby lowering combustion temperatures and reducing the formation of Nitrous Oxides (NOx). The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration and is controlled by various factors such as engine speed, altitude, engine vacuum, exhaust system backpressure, coolant temperature and throttle angle.
A malfunctioning EGR valve can cause 1 or more of the following:
Integral Backpressure Transducer EGR Valve
This poppet-type or tapered (pintle) valve cannot be opened by vacuum until the bleed hole is closed by exhaust backpressure. Once the valve opens, it seeks a level dependent upon exhaust backpressure flowing through the orifice and in so doing, oscillates at that level. The higher the signal vacuum and exhaust backpressure, the more the valve opens.Backpressure Variable Transducer EGR Valve
This exhaust gas recirculation system combines a ported EGR valve with a backpressure variable transducer in order to control nitrous oxides. The amount of exhaust gas reintroduced and the timing of the cycle varies by engine calibration and is controlled by various factors such as engine speed, altitude, engine vacuum, exhaust system backpressure, coolant temperature and throttle angle. The typical system consists of 3 components, a vacuum regulator, an EGR valve and a flow control orifice. The regulator modulates the vacuum signal to the EGR valve using 2 backpressure inputs. One input is the standard vehicle backpressure. The other is backpressure downstream of the flow control orifice. The control chamber sensor point is in the EGR tube. The flow control orifice is integral to the upstream EGR tube connector.PFE and DPFE EGR Systems
See Figures 1, 2, 3, 4 and 5
The Pressure Feedback Electronic (PFE) is a subsonic closed loop EGR system that controls the EGR flow rate by monitoring the pressure drop across a remotely located sharp-edged orifice. With a PFE system, the EGR valve only serves as a pressure regulator, rather than a flow metering device.
The Differential Pressure Feedback Electronic (DPFE) EGR system operates in the same manner as the PFE system, with the exception that it also monitors exhaust pressure in the exhaust system. This allows for a more accurate control of the recirculation gases.Electronic EGR System
See Figures 6 and 7
An electronic EGR valve is required in the Electronic Engine Control (EEC) systems where EGR flow is controlled according to computer demands by means of an EGR Valve Position (EVP) sensor attached to the valve. The valve is controlled according to signals sent from the EGR Vacuum Regulator (EVR). The EVP sensor, mounted on the valve, sends an electrical signal of its position to the Electronic Control Assembly (ECA).
Integral Backpressure Transducer EGR Valve
See Figure 8
- Check that all vacuum lines are properly routed, all connections are secured and the vacuum hoses are not cracked, crimped or broken.
- With the EGR valve at rest, air should flow freely when vacuum is applied to the signal vacuum nipple of the valve. Also the valve should not hold any vacuum at this time. If the valve does holds vacuum, clean or replace it, and perform the test again.
- With the vehicle at idle, there should be no vacuum going to the EGR valve. If there is, check for correct hose routing.
- With the engine at normal operating temperature, and the engine running at 3000 rpm, there should be vacuum going to the EGR valve. If there in no vacuum, check back through the vacuum lines from the EGR to source. Replace, as necessary.
See Figure 9
- Apply a minimum of 2.5 psi (5.0 in. Hg) of vacuum individually to the 3 ports of the EGR valve.
- The middle and bottom ports should hold vacuum, while the top port should not hold vacuum.
- If the previous results are not achieved, replace the valve.
REMOVAL & INSTALLATION
See Figures 10, 11, 12, 13, 14 and 15
- Locate the EGR valve at the rear of the engine compartment by the firewall. It can be found bolted to the engine, next to the brake booster.
- Using a suitable adjustable wrench, loosen the connection at the base of the valve. Loosen the collar, and push the fitting down. Do not move the tube. In most vehicles, this tube is thin metal and bends easily.
- Remove the nuts/studs securing the valve to the engine.
- Remove the EGR valve and gasket. Discard the gasket.
- Position the valve with a new gasket to the mounting surface on the engine.
- Secure the EGR valve with nuts/studs. Tighten the hardware to 15-3 ft. lbs. (5-8 Nm).
- Position the collar to the valve and tighten.
- Start the engine and check for air leaks around the fittings.