An Exhaust Gas Recirculation (EGR) system is fitted to 1997-98 California diesels.
Description & Operation
The EGR system reduces oxides of nitrogen in the engine exhaust. This is done by allowing a predetermined amount of hot exhaust gas to recirculate and dilute the incoming fuel/air mixture.
The following are the major components of the system:
When the PCM supplies a ground signal to the EGR valve vacuum regulator solenoid, the EGR system operation starts to occur. The PCM will monitor and determine when to supply and remove this ground signal. This will depend on inputs from the engine coolant temperature, throttle position and intake manifold air temperature sensors.
When the ground signal is supplied to the EGR solenoid, vacuum from the vacuum pump is allowed to pass through the EGR solenoid and on to the EGR valve with a connecting hose.
The EGR valve is normally open when the engine is running at idle or above with the coolant at normal operating temperature. Certain changes to engine status will close the valve, including rapid acceleration, wide-open throttle or after about two minutes without a change in throttle position.
Removal & Installation
- Pull off vacuum lines on both sides of the valve. A bit of penetrating fluid safe for rubber and plastic will aid removal.
- Check lines for cracking or damage and replace as required.
- When installing, be sure connections are clean and tight.
- Be sure the vacuum lines are properly connected. The inlet side of the valve is marked "S".
- Disconnect the vacuum line at the EGR.
- Remove the two bolts securing the EGR tube.
- Remove the EGR mounting bolts and remove the valve.
- Clean off old gasket material.
- Tighten bolts gradually and evenly. Torque to 18 inch lbs. (24 Nm).
- Disconnect the power steering hoses and the vacuum line.
- Remove the sender unit from the engine block and plug the hole.
- Remove and cap the oil feed line from the bottom of the vacuum pump.
- Remove the lower bolt that attaches the pump assembly to the engine block.
- Remove the nut from the steering pump attaching bracket.
- Remove the upper bolt from the assembly and remove the assembly.
- remove the steering pump to vacuum pump bracket attaching nuts.
- Reverse the removal procedure.
- Rotate the drive gear until the steering pump and vacuum pump drive dogs align. Install the steering pump onto the vacuum pump bracket. Use care to avoid damaging the oil seal.
- The steering pump housing and spacers must mate completely with the vacuum pump bracket.
- Tighten the bracket-to-steering pump nuts to 18 ft. lbs. (24 Nm). Tighten the pump-to-engine block attaching bolts to 57 ft. lbs. (77 Nm). Tighten the bracket nut to 18 ft. lbs. (24 Nm).
- A quick-release, one-way check valve is located in the vacuum line between the EGR valve and the vacuum regulator solenoid. Failure may result in the EGR not opening or remaining open when it should not.
- Attach a vacuum gauge with a "T" fitting into the vacuum line at the EGR valve between the EGR valve and EGR vacuum regulator solenoid.
- Run the engine until operating temperature is reached.
- Drive at a steady speed. Vacuum should be observed at the gauge.
- Quickly open the throttle. Vacuum should drop to "0".
- The check-valve can also be tested with a hand-held vacuum gauge connected to the inlet side of the valve (marked with an "S"). It should hold 20 inches of vacuum or more without leakage.
- The other side of the valve should not hold any vacuum.
- Remove the EGR valve from the manifold (see procedure below).
- Examine the head of the poppet valve at base opening on the bottom of the valve. Look for heavy carbon build-up. Some carbon build-up is normal.
- Shine a bright light through the valve opening and examine the valve seat. No light should be evident at the valve edge. Replace the EGR valve if either condition exists.
- Connect a vacuum pump to the EGR's vacuum pump fitting. Slowly apply about 10 inches Hg of vacuum. The valve should start to open. Vacuum should hold steady. If it doesn't, replace the valve.
- The valve should be fully open at 20 inches Hg of vacuum. If it isn't, replace it.
- Check all of the passages for carbon clogging. Cleaning is not practical. Replace any clogged valve.
- Disconnect the vacuum supply line at the EGR valve vacuum regulator solenoid and attach a vacuum gauge.
- Start the engine and check vacuum. It should range from 8-25 inches Hg as rpm varies.
If vacuum does not fall within this range, check for leaks in lines and connections. If the system is sound, replace the vacuum pump.