EGR System Ford Bronco II I

DESCRIPTION

The Exhaust Gas Recirculation (EGR) system is used to reduce NOx emissions. This is accomplished by recycling exhaust gases back into the intake manifold, resulting in cooler combustion temperatures and lower combustion pressure.

PORTED & INTEGRAL BACKPRESSURE SYSTEMS

Both systems are controlled by an EGR valve which is normally closed. Vacuum signals control the opening and closing of the EGR valve. When the EGR valve is closed, no exhaust gas is allowed to enter the intake manifold. If vacuum is applied, the valve opens and exhaust gas enters the manifold passages.

Some light duty emission systems use a backpressure transducer to aid in controlling exhaust gas recirculation. This unit senses exhaust gas backpressure and modulates vacuum signal to EGR valve in response to amount of backpressure. Backpressure is used to provide information on engine operation modes. The backpressure transducer is integral with the EGR valve. (Scheme 31)

EGR Valve Without Backpressure Transducer. Scheme 28

EGR CONTROL (EGRC) SOLENOID

The EGRC solenoid controls the vacuum signal to the EGR valve. The EGRC is normally closed, no voltage is applied to the EGRC, and no vacuum signal flows through the solenoid. When voltage is applied to the EGRC, the valve pintle opens and the vacuum signal passes through the solenoid to the EGR.

EGR VALVE POSITION (EVP) SENSOR

The EVP sensor input indicates the amount of EGR gases flowing into the intake manifold. When the EVP sensor indicates EGR gases are flowing, the Electronic Control Assembly (ECA) generally advances spark timing and the fuel injector pulse width is adjusted for changing EGR flow rates.

EGR VENT (EGRV) SOLENOID

The EGRV solenoid is used to vent the vacuum signal. The EGRV is normally open. If no voltage is applied to the EGRV, the vacuum vent remains open. This allows the vacuum signal to be vented to the atmosphere. When voltage is applied to the EGRV, the vent closes and the vacuum signal is trapped in the vacuum signal line.

ELECTRONIC EGR VALVE SYSTEM

The Electronic EGR Valve System is controlled by the ECA. An EVP sensor mounted on top of the EGR valve sends an electrical signal of the EGR valve's position to the ECA. The ECA sends an electrical signal to the Electronic Vacuum Regulator (EVR) to control vacuum to the EGR valve. (Scheme 29)

Electronic EGR Valve. Scheme 29

PRESSURE FEEDBACK ELECTRONIC SYSTEM

On the Pressure Feedback Electronic system an Electronic Pressure Sensor uses exhaust backpressure from the EGR valve to send a electrical signal to the ECA. The ECA uses this signal to send a signal to a EVR. This electrical signal is converted to a vacuum signal to control the EGR valve flow.

Electronic Vacuum Regulator & Pressure Sensor. Scheme 30

EGR VALVE WITHOUT BACKPRESSURE TRANSDUCER

1. Check that all vacuum lines are properly routed, all connections are secure, and that vacuum hoses are not cracked, crimped or broken. When engine is cold there should be no vacuum to operate the valve. If there is vacuum, check Ported Vacuum Switch (PVS) function. Replace if necessary. There should be no vacuum to valve at warm curb idle.
2. Vacuum should be available at or above part throttle with engine at operating temperature. If vacuum is not available, check PVS and replace as necessary.
3. With engine at idle, apply 8 in. Hg vacuum to EGR valve. Valve stem should move to open valve and produce a rough idle. If valve stem moves but idle does not change, remove valve and clean inlet and outlet ports with wire brush.
4. With engine at idle, trap 4 in. Hg vacuum in EGR valve and hold. Vacuum should not drop more than one in. Hg in 30 seconds. If vacuum drops, replace valve.

EGR Valve With Integral Backpressure Transducer Valve cannot be opened by vacuum until bleed hole is closed by exhaust backpressure. Scheme 31

EGR VALVE WITH INTEGRAL BACKPRESSURE TRANSDUCER

1. Clamp drive socket wrench into tailpipe. Socket outside diameter should be about 1/16" less than tailpipe inside diameter. Socket drive hole should be covered and socket should be inserted into tailpipe with open end facing out to ensure proper backpressure.
2. Do not block tailpipe fully or run engine faster than idle for prolonged periods of time. Be sure to remove socket from tailpipe at end of test.
3. Idle engine and apply vacuum to EGR valve gradually. EGR valve diaphragm should move smoothly and rough idle should occur. Trap 6 in. Hg vacuum in EGR valve and hold. Vacuum should drop more than one in. Hg in 30 seconds.
4. If vacuum does not drop or diaphragm does not move, replace valve. If diaphragm moves but idle does not change, remove valve and check for plugged inlet and outlet ports. Clean inlet and outlet ports with wire brush and install valve and retest.

ELECTRONIC EGR VALVE

Note. Electronic EGR Valve system is controlled by the EEC system. This article covers testing of EGR valve only. Refer to appropriate article in the COMPUTERIZED ENGINE CONTROL section for testing of EVP sensor and Electronic Vacuum Regulator.

1. Check vacuum lines for correct routing. Disconnect vacuum hose at valve and connect vacuum gauge to hose. Disconnect connector at EVP on top of EGR valve.
2. Start engine and apply 8 in. Hg of vacuum with engine idling. Engine idle should become rough or stall. If idle did not drop, remove valve and check for plugged inlet or outlet ports. Clean ports if they are plugged. Replace valve if inlet or outlet ports are not plugged.

Note. Refer appropriate article in the COMPUTERIZED ENGINE CONTROL section for diagnosis of Pressure Feedback Electronic EGR system.

PVS with 2 Connections

1. Detach both vacuum hoses from PVS, and connect vacuum gauge to top port on PVS. Connect other PVS nipple to manifold vacuum or external vacuum supply of at least 10 in. Hg. (Scheme 32)
2. Start engine and warm until engine operating temperature is reached. If no vacuum reading is noted, PVS should be replaced. If vacuum is present, PVS is okay.

Cutaway View of 2-Port PVS PVS will open when engine reaches operating temperature. Scheme 32

Scheme 33

1. Disconnect vacuum hoses at PVS valve. Connect vacuum gauge to top port of PVS. Connect external vacuum source to second port. (Scheme 34)
2. Start engine and warm up until engine operating temperature is reached. If there is no vacuum, this portion of PVS is damaged and valve should be replaced. If vacuum is present, proceed to next step. (Scheme 33): Cutaway View of 3-Port PVS Warm engine should indicate vacuum at center PVS port.
3. Connect gauge to third port and vacuum supply to bottom port. If vacuum is noted, PVS is okay. If no vacuum, replace PVS.

Cutaway View of 4-Port PVS Connect vacuum gauge to first and third port to check PVS. Scheme 34

VENTURI VACUUM AMPLIFIER

Note. Amplifiers have built-in calibrations, and no external adjustments are required. If amplifier bias test reveals malfunction, replace amplifier. Always check venturi vacuum amplifier last, after checking all other basic EGR components.

1. With engine at normal operating temperature, curb idle set and adequate manifold vacuum supplied to system, connect vacuum gauge to hose at amplifier port "O". (Scheme 35) Gauge may read as much as 2 in. Hg at idle.
2. Disconnect venturi hose (amplifier port "V") at carburetor and increase engine speed to 2000-3000 RPM. Vacuum should not change.
3. While maintaining high engine speed, connect venturi hose. Vacuum should increase to 4 in. Hg. Return to idle. Gauge should return to initial reading. If amplifier does not perform as specified, replace amplifier.

Testing Venturi Vacuum Amplifier. Scheme 35

VACUUM AMPLIFIER RESERVOIR

When charged with 15-20 in. Hg vacuum, vacuum loss should not exceed .5 in. Hg in 60 seconds. If it does, replace reservoir.

EGR REMINDER LIGHT RESET PROCEDURE

1. Turn ignition off. Insert Phillips screwdriver into hole in timer unit. While lightly pushing screwdriver in, turn ignition switch to the "RUN" position.
2. With EGR reminder light on, hold screwdriver in place for 5 seconds. Remove screwdriver. Reminder light should go out in 2-5 seconds. If not, repeat steps 1) and 2).
3. Turn ignition off. Turn ignition switch to the "RUN" position. Reminder light should come on for 2-5 seconds and then go out. This checks proper reset of light module.

Note. Reminder light is activated by an electronic module which senses engine-on time rather than actual mileage. Reminder light is designed to come on at approximately 60,000 miles.