DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is designed to reintroduce small amounts of exhaust gas into the combustion cycle, thus reducing the amounts of NOx emissions. 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 tank, check valve, and a Ported Vacuum Switch (PVS) and/or a Temperature Vacuum Switch (TVS).
There are 4 basic types of EGR valves. They are Integral Backpressure Valve, Ported EGR Valve, Electronic EGR Valve and Valve and Transducer Assembly EGR Valve, which is a modified Ported EGR Valve.
The Backpressure Variable Transducer (BVT) system is used on some models. This system combines a ported EGR valve with a Backpressure Variable Transducer (BVT) to control NOx emissions. Typical components included in this system are EGR Valve, PVS or TVS and carburetor EGR port or vacuum tank vacuum source.
Models with Electronic Engine Control (EEC) systems use an electronic EGR system with an electronic EGR valve with a EGR-Valve Position (EVP) sensor. In addition, these vehicles use an exhaust cooler which uses coolant to reduce the temperature of exhaust flowing through the EGR valve and into the engine. System also has EGR Solenoid Vacuum Valve Assembly.
Some selected 2.0L and 2.3L engines use an EGR valve and transducer assembly which consists of an external entry ported EGR valve and a pressure tap to provide a backpressure signal to a remote transducer. This system operates the same as the integral backpressure transducer valve system. Function checks are the same as that system.
Integral Backpressure Transducer Valve
This valve combines inputs of backpressure and EGR port vacuum into one unit. Both inputs are required for valve to operate. There are two types of backpressure valves, poppet and tapered pintle. The Integral Backpressure Transducer Valve combines an exhaust gas backpressure transducer within diaphragm housing of EGR valve. Transducer modulates EGR flow by venting vacuum in relation to exhaust backpressure. Backpressure is sensed between inlet and poppet/tapered stem of valve. Flow rate is dependent on source vacuum, exhaust pressure, control setting and orifice size.
Poppet type valves are rapid opening. Flow rate through valve is limited by size of valve orifice or opening in carburetor spacer plate.
Internal tapered stem type valves use a pintle which moves tapered portion of valve up or down against valve seat. Gas flow rate is determined by amount of movement of taper off seat.
Integral Backpressure Transducer EGR Valve Valve with bottom entry, poppet type shown. Scheme 44
Ported EGR Valve
This valve is operated by a vacuum signal from carburetor EGR port which actuates valve diaphragm. As vacuum increases enough to overcome power spring, valve is opened, allowing EGR flow. Amount of flow is dependent on pintle or poppet position which is a direct result of vacuum signal.
Ported EGR Valve Valve with side entry, tapered pintle shown. Scheme 45
Electronic EGR Valve
This valve is operated by a vacuum signal from the dual EGR Solenoid Valves or the electronic vacuum regulator which actuates the diaphragm. As vacuum overcomes the spring load, the diaphragm is actuated and the pintle is lifted off its seat. Exhaust gas then flows. Flow amount is proportional to pintle position. The EVP sensor on the valve sends an electrical signal position to the Electronic Control Assembly.
The Electronic EGR Valve Assembly is not serviceable. EVP sensor and EGR valve must be serviced separately. A sensor mounted on top of this valve sends out electrical signals that tells Electronic Control Assembly (ECA) how far EGR valve is open.
ECA then signals EGR control solenoids to maintain or alter EGR flow as required. Source vacuum is from manifold, and is bled off or applied to diaphragm by ECA. A cooler is sometimes used to reduce gas temperature, reduce 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. Scheme 46
EGR LOAD CONTROL (WOT) VALVE
This valve dumps EGR vacuum at or near wide open throttle. Senses venturi vacuum at a predetermined level and causes valve to close or open when engine load is reduced from wide open throttle.
EGR VACUUM REGULATOR CONTROL SYSTEM
This system is used on most 1.6L and 2.3L engine applications. System consists of 3 components, a vacuum regulator, EGR valve and a flow control orifice. On EFI models, control chamber pickup is in EGR tube and flow control orifice is integral with upstream EGR tube inlet connector.
On all others, control chamber pickup and orifice are integral with 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 most 1.6L & 2.3L engines. Scheme 47
EGR VACUUM AMPLIFIER
Vacuum amplifier uses a relatively weak venturi vacuum to control a manifold vacuum signal to operate EGR valve. It contains a check valve and relief valve that opens whenever vacuum signal is equal to or greater than manifold vacuum.
TEMPERATURE VACUUM SWITCH
Switch has a normally open bimetal disc which allows free air flow in vacuum line. When closed, it blocks air flow by sealing against an "O" ring. It is used to hold off EGR to provide better cold driveability.
PORTED VACUUM SWITCH
Switch is a temperature actuated switch which changes vacuum connections when coolant temperature changes. It is used to hold off EGR to provide better cold driveability.
EGR SOLENOID VACUUM VALVE ASSEMBLY
The dual EGR solenoid valve assembly consists of two dithering valves, a vacuum valve that supplies vacuum to the sonic EGR valve when it is energized and a vent valve that vents EGR to atmosphere when de-energized. Both 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. 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 Valves
- 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 4000 RPM on 1.6L engines, 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. CAUTION: Do not block tailpipe fully and do not run engine faster than idle for prolonged periods. Be sure to remove plug from tailpipe at end of test. If these precautions are not followed, engine and/or exhaust system damage may occur.
- Trap 6 in. Hg vacuum and hold. Vacuum should 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 test is not okay, 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 4000 RPM on 1.6L engines, 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.
Electronic Sonic EGR Valve
- Connect vacuum gauge to valve. Apply 6 in. Hg vacuum to valve and trap. Vacuum should not drop more than 1 in. Hg in 30 seconds. If so, replace valve, "O" ring or EVP sensor.
- As sonic valve is part of EEC system, check all circuitry as described in EEC 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/thunderbird/ix-1983-1988/remont/testing-diagnostics/#egr-system-gasoline) .
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 4000 RPM on 1.6L engines, 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 48
See also:
• TROUBLE SHOOTING