DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is designed to reintroduce small amounts of exhaust gas into the combustion cycle thereby lowering combustion temperatures due to lower concentrations of oxygen. This lowering of combustion temperatures reduces the amount of NOx emissions produced by the engine. The amount of exhaust gas recycled and the timing of the cycle are controlled by such factors as engine vacuum, exhaust system backpressure, altitude, temperature, throttle angle and engine speed.
Typical systems consist of an EGR valve, carburetor EGR port, vacuum reservoir , check valve, and a Ported Vacuum Switch (PVS) and/or a Temperature Vacuum Switch (TVS).
Ford Motor Co. uses 4 basic types of EGR valves. They are integral backpressure EGR valve, ported EGR valve, electronic EGR valve and backpressure transducer EGR valve which is a modified Port EGR Valve with separate backpressure variable transducer.
The EGR Backpressure Variable Transducer (BVT) system is used on few models. This system combines a ported EGR valve with a backpressure variable transducer to control NOx emissions. Typical components included in this system are an EGR valve, a PVS or TVS and a carburetor EGR port or vacuum tank vacuum source.
Models with Electronic Engine Control (EEC) systems use an electronic EGR valve with a EGR Valve Position (EVP) sensor controlled by a vacuum solenoid assembly. In addition, this system uses an exhaust cooler which uses coolant to reduce the temperature of the exhaust flowing through the EGR valve.
Some selected 2.0L and 2.3L engines use an EGR valve and transducer assembly which consists of a ported EGR valve and a pressure tap to provide a backpressure signal to a remote backpressure transducer. This system operates the same as the integral backpressure transducer valve system. Functional checks are also the same on this system.
Integral Backpressure Transducer
This EGR valve combines inputs of exhaust backpressure and EGR port vacuum into one unit. Both inputs are required for the valve to operate. There are two types of exhaust backpressure valves, poppet and tapered pintle. The integral backpressure transducer valve combines an exhaust gas backpressure transducer within its diaphragm housing. The transducer controls EGR function by venting control vacuum in relation to exhaust backpressure.
In order for this valve to operate, sufficient exhaust backpressure is required to close a bleed valve located inside the vacuum diaphragm housing. Until this bleed valve closes all vacuum routed to the valve has no effect. When the bleed valve closes vacuum is then applied to the diaphragm and the valve opens allowing exhaust gas to flow. Flow rate is dependent on source vacuum, exhaust pressure, control setting and orifice size.
Poppet type valves are rapid opening. Flow rate through this valve is limited by size of valve orifice or opening in carburetor spacer plate.
Internal tapered stem type valves use a pintle which moves the tapered portion of the valve up or down against its valve seat. Flow rate is determined by the amount of movement off the seat.
Integral Backpressure Transducer EGR Valve Valve with bottom entry, poppet type shown. Scheme 31
Ported EGR Valve
This valve is operated by a vacuum signal from the carburetor EGR port which actuates the EGR valve diaphragm. When vacuum is increased enough to overcome the diaphragm closing spring pressure, the valve opens allowing EGR flow. Amount of flow is dependent on pintle or poppet position which is a direct result of the strength of the vacuum signal and valve type.
Ported EGR Valve Valve with side entry, tapered pintle shown. Scheme 32
Electronic EGR Valve
This valve is operated by a vacuum signal from one of the dual EGR solenoid valves or the electronic vacuum regulator which actuates the diaphragm. As vacuum overcomes the closing spring pressure, the diaphragm is actuated lifting the pintle off its seat and exhaust gas begins to flow. Flow is proportional to pintle position. The EVP sensor on the valve sends an electrical signal relevant to valve position to the Electronic Control Assembly. (Scheme 35)
The electronic EGR valve assembly is not serviceable. EVP sensor and EGR valve must be serviced separately. The EVP sensor mounted on top of this valve sends out electrical signals to the Electronic Control Assembly (ECA) that indicate how far the EGR valve is open.
The ECA then signals the EGR control solenoids to maintain or alter EGR flow as required. Source vacuum is obtained from the intake manifold and is bled off or applied to the EGR diaphragm by the ECA. A cooler is sometimes used to reduce gas temperatures and detonation and allow better gas flow. This valve operates only at part throttle mode. It is closed in all other modes.
Electronic EGR Valve System System used with EEC equipped vehicles only. Scheme 33
EGR LOAD CONTROL (WOT) VALVE
This valve dumps EGR vacuum at or near wide open throttle. This valve senses venturi vacuum at a predetermined level and causes the EGR valve to close. When engine load is then reduced from wide open throttle, the EGR load control valve closes and completes the vacuum pathway to the EGR.
EGR VACUUM REGULATOR CONTROL SYSTEM
This system is used on 2.3L engine applications. The system consists of 3 components, a vacuum regulator, EGR valve and a flow control orifice. On EFI models the control chamber pick-up is in the EGR tube and the flow control orifice is integral with upstream EGR tube inlet connector.
On all other models, the control chamber pick-up and orifice are integral with the EGR valve. Regulator receives a vacuum signal to modulate EGR valve using 2 backpressure inlets. One input is standard vehicle backpressure and other is backpressure downstream of flow control orifice.
EGR Vacuum Regulator Control System System used on 2.3L engines. Scheme 34
EGR VACUUM AMPLIFIER
Because venturi vacuum is not sufficient to operate the diaphragm of the EGR valve, a vacuum amplifier is used. This amplifier steps up the signal of venturi vacuum to a level that can control the EGR valve. This amplifier also contains a check and relief valve that opens whenever vacuum signal is equal to or greater than manifold vacuum.
TEMPERATURE VACUUM SWITCH
The temperature vacuum switch is used to hold off EGR operation to provide better cold engine driveability. This switch contains a normally open bi-metallic disc which allows free airflow in vacuum line. When closed, it blocks airflow by sealing against an "O" ring.
PORTED VACUUM SWITCH
The ported vacuum switch is used to hold off EGR operation to provide better cold engine driveability. This switch is temperature actuated which changes vacuum routing when coolant temperature changes.
EGR SOLENOID VACUUM VALVE ASSEMBLY
The dual EGR solenoid valve assembly consists of one vacuum valve that supplies vacuum to the EGR valve when it is energized and a vent valve that vents EGR vacuum to the atmosphere when de-energized. Both valves receive signals from the ECU. A restrictor is added in the vacuum valve inlet port so that the vent valve may vent if the vacuum valve sticks open.
ENGINE STALLS ON DECELERATION
EGR valve stuck open, or not closing fully.
ROUGH IDLE, STALLING, SURGE ROUGH RUNNING, HESITATION & POOR PART THROTTLE PERFORMANCE
EGR valve receiving vacuum from misrouted hoses. EGR valve not closing fully or stuck open, blown gasket or attachment loose, air bleeds plugged (backpressure valves). TVS or PVS opening too early when engine cold. EFI computer malfunction. Vacuum regulator leaking (BVT system).
PART THROTTLE ENGINE DETONATION
EGR valve stuck closed. Leaky valve diaphragm, vacuum restricted to EGR valve, EGR disconnected. TVS and/or PVS not opening, load control valve venting, EGR passages blocked. Insufficient backpressure. EVP sensor "O" ring leaking or sensor loose (EEC).
VERY LOW POWER AT FULL THROTTLE
Load control (WOT) valve not venting or EGR valve stuck open.
ENGINE HARD TO START, NO START, OR STARTS & STALLS
Vacuum at EGR. Vacuum hoses misrouted. EGR valve stuck open. PVS malfunction
POOR FUEL ECONOMY
If EGR related, usually accompanied by detonation or other symptom of restricted or no EGR flow.
Integral Backpressure Transducer Valve
- Disconnect vacuum line to EGR valve and plug. Connect vacuum pump to valve. Start engine and idle. Apply 6 in. Hg vacuum to valve. Vacuum should bleed off and valve should not operate.
- If vacuum holds and valve opens, replace valve. With engine at idle, there should be no vacuum to valve. If so, check vacuum hose routing. With engine cold, there should be no vacuum to valve. If so, check TVS or PVS and replace as required.
- With engine warm, there should be vacuum to valve at 3000 RPM for 2.3L engines, and kickdown RPM on all other engines. If not, check vacuum lines from EGR to source.
- Into end of tailpipe, clamp a plug about 1/16" less in diameter than I.D. of tailpipe. A drive socket with drive hole covered may be used. Idle engine and apply vacuum gradually. Valve stem/diaphragm should move smoothly and engine idle should roughen.
- Apply 6 in. Hg vacuum to the EGR valve and hold. Vacuum should not drop more than 1 in. Hg in 30 seconds. If valve test is okay but engine does not idle rough in test, clean valve passages. If problem persists, replace valve.
- With engine cold there should be no vacuum to valve. If vacuum exists, check TVS or PVS function. At warm curb idle there should be no vacuum to valve.
- With engine warm, there should be vacuum to valve at 3000 RPM for 2.3L engines, and 2000 RPM on all other engines. If not, check vacuum lines, TVS and PVS and replace as required.
- With engine at idle, apply 8 in. Hg vacuum to valve. Valve stem should move, opening valve and idle should roughen. If stem moves but idle does not roughen, clean valve passages.
- With engine idling, apply 4 in. Hg vacuum to valve and trap. Vacuum should not drop more than 1 in. Hg in 30 seconds. If so, replace valve.
- Connect vacuum gauge to valve. Apply 6 in. Hg vacuum to valve and hold. Vacuum should not drop more than 1 in. Hg in 30 seconds. If so, replace valve, "O" ring or EVP sensor.
- As electronic EGR valve is part of EEC system, check all circuitry. See ELECTRONIC ENGINE CONTROL IV THEORY, OPERATION & TESTING article. Mechanical function can be checked as follows
- Check vacuum lines for correct routing. Disconnect vacuum hose at valve and connect vacuum gauge to hose. Accelerate engine to 2000-2500 RPM and release throttle. Repeat 8-10 times and check for consistent response.
- If vacuum rises above zero, when is engine cold, diaphragm is leaking and valve should be replaced. With engine warm, vacuum should rise above 15 in. Hg and return to zero when throttle is released.
- If vacuum does not go to 15 in. Hg, check vacuum source and service. If vacuum does not return to zero or is inconsistent, solenoid is worn and should be replaced. If solenoid is not damaged, and symptoms still exist, see «TROUBLE SHOOTING»(/ford/ltd-crown-victoria/i-1983-1991/remont/testing-diagnostics/#egr-system) .
VACUUM AMPLIFIER
- Check for adequate manifold vacuum. With engine warm and at curb idle, connect vacuum gauge to port "O" on amplifier which leads to EGR/PVS valve. Vacuum should not read more than 2 in. Hg at idle.
- Disconnect venturi hose at carburetor. Increase engine speed to 3000 RPM on 2.3L engines, and 2000 RPM on all other engines. Vacuum should not change. Maintain high engine speed and reconnect venturi hose.
- Gauge should register at least 4 in. Hg vacuum. Return engine to idle. Gauge should return to initial reading. If not, replace amplifier.
Electronic EGR Valve Assembly Side (External) entry type is shown. Scheme 35
See also:
• TROUBLE SHOOTING