DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is used to help control formation of NOx emissions. The EGR introduces exhaust gases back into intake system. The exhaust gases lower top combustion temperatures, which help keep NOx emissions down.
The system consists of an EGR valve, EGR pipe and thermo vacuum valve. An EGR leak orifice is used on MPI models, and also on federal models with manual transmissions.
OPERATION
EGR valve receives operating vacuum from carburetor ported vacuum (throttle body for fuel injected models). A thermo vacuum valve, used on all carbureted models, bleeds off vacuum to EGR valve when intake manifold temperature is below 86°F (30°C). When intake manifold temperature reaches 104°F (40°C), vacuum bleed off stops and normal EGR operation begins.
To control vacuum bleed off, an EGR leak orifice is used. This vacuum bleed off system is used on MPFI models and, also on Federal models with manual transmissions.
On all fuel injected models, EGR operating vacuum is controlled by a combination of the ECU and the EGR solenoid valve. This system does not allow EGR operation until engine reaches normal operating temperature or at wide open throttle.
Scheme 11
Scheme 12
Scheme 13
Scheme 14
EGR VALVE
- Look through opening in EGR valve body. With engine at normal operating temperature, check that valve shaft moves when engine reaches 3000-3500 RPM under no-load condition.
- If shaft does not move as specified, remove valve and manually check valve movement. If valve appears okay, check vacuum lines for leaks. If valve does not operate, clean or replace. NOTE: When cleaning EGR valve, DO NOT wash in solvent or degreaser or permanent damage to the valve diaphragm will result.
- While holding valve assembly by hand, lightly tap on sides and end of valve with plastic hammer to remove exhaust deposits from the valve seat. DO NOT place unit in a vise.
- Using wire wheel, buff the exhaust deposits from around mounting surface and valve. Depress valve diaphragm, look through valve outlet and inspect valve seat area for cleanliness. Repeat cleaning operation if not completely clean.
- Inspect valve outlet for deposits and clean as necessary. Blow clean with compressed air. Recheck valve operation by applying 7.87 in. Hg with a hand vacuum pump. Install unit using a new gasket.
EGR SOLENOID VALVE
- Remove connector from solenoid valve. Measure resistance between solenoid valve terminal leads. Specified resistance is 32.7-29.9 ohms. If measurement is out of specifications, replace solenoid valve.
- If resistance measurement in step 1) is okay, measure resistance between solenoid valve terminal leads and body ground. Specified resistance is 1000 ohms or more. If measurement is out of range, replace solenoid valve.
- Check vacuum passage for opening and closing operation while applying electric current to positive and then negative terminals. If solenoid valve does not operate properly, replace with a new one. If solenoid operates properly through all tests, valve is normal.
Scheme 15
- Remove valve from intake manifold. Connect hoses to the output ports for air cleaner and EGR valve (2 upper ports) and plug output port to canister (one lower port). (Scheme 15) Submerge valve into a container of cold water. NOTE: DO NOT allow water to enter valve.
- Heat slowly to raise temperature of water. Blow air into valve and confirm valve opens or closes in response to water temperature.
- Thermo vacuum valve should completely open below 86°F (30°C) and should completely close above 104°F (40°C). Remove thermo valve from water. Connect vinyl tubes to output ports to EGR valve and canister, and plug output port to air cleaner with a cap.
- Blow air into valve and confirm that valve opens and closes in response to water temperature. Valve should completely open below 86°F (30°C) and should completely close above 104°F (40°C).
Multi-Point Fuel Injected Engines
Ensure there is no air flowing from EGR solenoid valve side, to air intake boot side. Ensure there is air flowing from air intake side to EGR solenoid valve side.
- If both EGR valve and thermo vacuum valve are functioning correctly, apply about 7.87 in. Hg to EGR valve with hand vacuum pump. With engine warmed up, either rough idling or engine stall should occur.
- If engine idle does not change, check EGR pipe and gas passages for clogging and leaks. Clean or replace if necessary. When cleaning, inspect EGR gas inlet to intake manifold for presence of deposits.
- Remove any deposits present using a hooked awl. Take extreme care that deposits DO NOT fall into intake manifold. DO NOT use an electric drill for cleaning. Remove deposits using a vacuum device.
- Inspect EGR gas inlet pipe for exhaust deposits and remove pipe as needed. Tap lightly on sides of pipe to loosen deposits. Clear deposits in pipe by using compressed air. Reassemble and install pipe.