See Figures 1 and 2
The 2.3L (VIN A) and 1991-92 3.8L engines do not use an EGR valve.
The EGR system is used to reduce oxides of nitrogen (NOx) emission levels caused by high combustion chamber temperatures. This is accomplished by the use of an EGR valve which opens, under specific engine operating conditions, to admit a small amount of exhaust gas into the intake manifold, below the throttle plate. The exhaust gas mixes with the incoming air charge and displaces a portion of the oxygen in the air/fuel mixture entering the combustion chamber. The exhaust gas does not support combustion of the air/fuel mixture but it takes up volume, the net effect of which is to lower the temperature of the combustion process. This lower temperature also helps control detonation.
The EGR valve is a mounted on the intake manifold and has an opening into the exhaust manifold. Except for the digital and linear versions, the EGR valve is opened by manifold vacuum to permit exhaust gas to flow into the intake manifold. With the digital and linear versions, the EGR valve is purely electrical and uses solenoid valves to open the flow passage. If too much exhaust gas enters, combustion will not occur. Because of this, very little exhaust gas is allowed to pass through the valve. The EGR system will be activated once the engine reaches normal operating temperature and the EGR valve will open when engine operating conditions are above idle speed and below Wide Open Throttle (WOT). On California vehicles equipped with a Vehicle Speed Sensor (VSS), the EGR valve opens when the VSS signal is greater than 2 mph (3.2 kph). The EGR system is deactivated on vehicles equipped with a Transmission Converter Clutch (TCC) when the TCC is engaged.
Too much EGR flow at idle, cruise, or during cold operation may result in the engine stalling after cold start, the engine stalling at idle after deceleration, vehicle surge during cruise and rough idle. If the EGR valve is always open, the vehicle may not idle. Too little or no EGR flow allows combustion temperatures to get too high which could result in spark knock (detonation), engine overheating and/or emission test failure.
There are four basic types of systems as described below, differing in the way EGR flow is modulated.Integrated Electronic EGR Valve
See Figure 3
The integrated electronic EGR vave, used on 1988-89 engines, functions like a port valve with a remote vacuum regulator, except the regulator and a pintle position sensor are sealed in the black plastic cover. The regulator and position sensor are not serviceable items; there is a serviceable filter that provides fresh air to the regulator, along side the vacuum tube.
This valve has a vacuum regulator, to which the ECM provides variable current. This current produces the desired EGR flow using inPuts from the manifold air temperature sensor, coolant temperature sensor and engine rpm.Negative Backpressure EGR Valve
See Figure 4
The negative backpressure EGR valve, used on the 2.5L engine, varies the amount of exhaust gas flow into the intake manifold depending on manifold vacuum and variations in exhaust backpressure. An air bleed valve, located inside the EGR valve assembly acts as a vacuum regulator. The bleed valve controls the amount of vacuum in the vacuum chamber by bleeding vacuum to outside air during the open phase of the cycle. The diaphragm on the valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure. Engine vacuum opens the EGR valve against the pressure of a spring. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes. This valve will open if vacuum is applied with the engine not running.Digital EGR Valve
See Figure 5
The digital EGR valve, used on all 1990 and later EGR-equipped engines (Except the 2.5L and 1994-96 3.8L engine) is designed to control the flow of EGR independent of intake manifold vacuum. The valve controls EGR flow through 3 solenoid-opened orifices, which increase in size, to produce 7 possible combinations. When a solenoid is energized, the armature with attached shaft and swivel pintle, is lifted, opening the orifice.
The digital EGR valve is opened by the ECM, grounding each solenoid circuit individually. The flow of EGR is regulated by the ECM which uses information from the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS) and Manifold Absolute Pressure (MAP) sensor to determine the appropriate rate of flow for a particular engine operating condition.Linear EGR Valve
THe linear EGR valve, used on the 1994-96 3.8L engine, is designed to accurately supply EGR to an engine, independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The PCM uses information from the Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor and the Mass Air Flow (MAF) sensor to determine the appropriate rate of flow for a particular engine operating condition.
Negative Backpressure EGR Valve
- Inspect all passages and moving parts for plugging, sticking and deposits.
- Inspect the entire system (hoses, tubes, connections, etc.) for leakage. Replace any part that is leaking, hardened, cracked, or melted.
- Run the engine to normal operating temperature, and allow the engine to idle for 2 minutes. Quickly accelerate the engine to 2,500 rpm. Visible movement of the EGR stem should occur indicating proper system function. If no movement occurs, check the vacuum source and hose.
- To determine if gas is flowing through the system, connect a vacuum pump to the valve.
- With the engine idling, slowly apply vacuum. Engine speed should start to decrease when applied vacuum reaches 3 in. Hg. (10 kPa) The engine speed may drop quickly and could even stall; this indicates proper function.
- If engine speed does not drop OFF, remove the EGR valve and check for plugged passages. If everything checks out, replace the valve.
This system must be checked using a Tech 1®or equivalent scan tool. Steps 4, 5 and 6 must be done very quickly, as the ECM will adjust the idle air control valve to compensate for idle speed.
- Using a Tech 1®or equivalent scan tool, check for any diagnostic trouble codes and solve those problems first. Refer to the Diagnostic Trouble Code (DTC) lists later in this section.
- Select "EGR CONTROL'' on the scan tool.
- Start and run the engine, until it reaches normal operating temperature, then allow the engine to idle for 2 minutes.
- Energize EGR SOL #1; engine rpm should drop slightly.
- Energize EGR SOL #2; the engine should have a rough idle.
- Energize EGR SOL #3; the engine should idle rough or stall.
- If all tests were as specified, the system is functioning properly.
- If not, check the EGR valve, pipe, adaptor, gaskets, fittings, and all passages for damage, leakage or plugging. If all is OK, replace the EGR valve assembly.
See Figure 6
To check this system, refer to the accompanying diagnostic chart for 1994-96 3.8L engines.Integrated Electronic EGR Valve
See Figure 7
To check this system, refer to the accompanying diagnostic chart.
REMOVAL & INSTALLATION
See Figure 8
- Disconnect the negative battery cable.
- If necessary for access, remove the air cleaner assembly.
- Tag and disconnect the necessary hoses and wiring to gain access to the EGR valve.
- Unfasten the EGR valve retaining bolts.
- Remove the EGR valve and gasket. Discard the gasket.
- Buff the exhaust deposits from the mounting surface and around the valve using a wire wheel.
- Remove deposits from the valve outlet.
- Clean the mounting surfaces of the intake manifold and valve assembly.
- Install a new EGR gasket.
- Position the EGR valve to the manifold.
- Install the retaining bolts and tighten to 16 ft. lbs. (22 Nm).
- Connect the wiring and hoses.
- Install the air cleaner assembly, if removed.
- Connect the negative battery cable.
See Figures 9, 10, 11, 12 and 13
- Disconnect the negative battery cable.
- Detach the electrical connector from the solenoid.
- Unfasten the 2 base-to-flange bolts, then remove the digital EGR valve.
- Remove and discard the gasket. Thoroughly clean the gasket mating surfaces.
- Position a new gasket, then install the digital EGR valve.
- Install the 2 base-to-flange bolts. Tighten to 22 ft. lbs. (30 Nm).
- Attach the electrical connector to the solenoid.
- Connect the negative battery cable.