DESCRIPTION
Note. California models with 6.2L diesel engines use an electronic EGR control system. See SELF-DIAGNOSTICS article.
Purpose of the Exhaust Gas Recirculation (EGR) system is to limit formation of oxides of nitrogen (NOx) emissions. This is done by reducing high peak combustion temperatures at which NOx is formed. By reintroducing a small amount of exhaust gas back into the combustion chamber, high temperatures are avoided and thus NOx emissions formation is reduced.
EGR system consists of, EGR valve, exhaust pressure regulator (EPR), EGR solenoid, EPR solenoid, throttle position switch (TPS) and vacuum pump.
OPERATION
EGR valve installed on intake manifold, introduces exhaust gases to incoming fresh air at engine crossover. EPR valve installed between exhaust manifold and exhaust pipe, is used to increase exhaust backpressure during idle which increases exhaust flow through the EGR system.
Diesel EGR Valve. Scheme 40
SYSTEM TESTING
- Warm-up engine to normal operating temperature. Remove air cleaner cover to observe operation of EGR valve.
- With engine at idle, EGR valve should be open. If valve does not open, check and correct any electrical and hose connection which may be loose or disconnected.
- Remove vacuum hose from EGR valve. Valve head should drop with noticeable reduction in noise. Reconnect hose.
- At idle, hose to EGR valve should have about 20 in. Hg. If vacuum is not present, check output to vacuum pump at pump. Pump should produce a minimum of 20 in. Hg.
- If vacuum is present at EGR valve but valve does not open and close as the hose is put on and taken off, EGR valve is stuck and should be checked and replaced if necessary.
- Manually operate throttle lever at injection pump through 15° to 20° of travel. EGR valve should close when TPS reaches calibrated point.
- Check Pink wire to TPS for 12 volts (key on). If 12 volts is not present, check for any loose connections, open wire and blown 20 amp gauge fuse. Correct any loose wire connections and/or change fuse.
- With key on, Blue wire from TPS switch should also have 12 volts. Blue wire feeds EPR solenoid. At idle, if Pink wire has 12 volts but Blue wire does not, TPS is inoperative and should be changed.
- With engine off, key on, operate throttle through 20° travel. At about 15°, TPS will cut out the 12 volts to Blue wire (EPR). At about 20°, TPS will cut in 12 volts to Yellow wire (EGR). If not, TPS is inoperative.
- Check all electrical connections at EGR-EPR solenoid assembly. Check that all hoses are routed correctly and connected to the solenoids. If vacuum is present at solenoids and solenoids are receiving an electrical signal as previously mentioned and operation of TPS through the calibrated points does not operate the EGR and/or EPR valves, solenoid assembly is inoperative and should be replaced.