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Exhaust Gas Recirculation (EGR) system - general information, checking and component renewal
Emissions control systems / Exhaust Gas Recirculation (EGR) system - general information, checking and component renewal


General information
1 To reduce oxides of nitrogen (NOx) emissions, some of the exhaust gases are recirculated through the EGR valve to the inlet manifold. This has the effect of lowering combustion temperatures.

2 The system consists of the EGR valve, the EGR exhaust gas pressure differential sensor, the EGR solenoid valve, the ECU, and various sensors - see illustration 2.1A. The ECU is programmed to produce the ideal EGR valve lift for each operating condition.

Checking
EGR valve
3 Start the engine and allow it to idle.

4 Detach the vacuum hose from the EGR valve, and attach a hand vacuum pump in its place.

5 Apply vacuum to the EGR valve. Vacuum should remain steady, and the engine should run poorly.

(a) If the vacuum doesnt remain steady and the engine doesnt run poorly, renew the EGR valve and recheck it.

(b) If the vacuum remains steady but the engine doesnt run poorly, remove the EGR valve, and check the valve and the inlet manifold for blockage. Clean or renew parts as necessary, and recheck.

EGR system
6 Any further checking of the system requires special tools and test equipment. Take the vehicle to a dealer service department for checking.

Component renewal
Note: These components will be very hot when the engine is running. Always allow the engine to cool down fully before starting work, to prevent the possibility of burns.

EGR valve
7 Disconnect the battery negative (earth) lead - see Section 1 of Chapter 5.

8 Remove the air mass meter and resonator - refer to Chapter 4.

9 Detach the vacuum hose, unscrew the sleeve nut securing the EGR pipe to the valve, remove the two valve mounting bolts, and withdraw the valve from the inlet manifold (see illustrations). Ensure that the end of the pipe is not damaged or distorted as the valve is withdrawn, and note the valves gasket; this must be renewed whenever the valve is disturbed.

6.9A Disconnecting vacuum hose from Exhaust Gas Recirculation (EGR) valve . .
6.9A Disconnecting vacuum hose from Exhaust Gas Recirculation (EGR) valve . . .

6.9B . . . unscrew EGR pipe sleeve nut and remove bolts (arrowed) to release
6.9B . . . unscrew EGR pipe sleeve nut and remove bolts (arrowed) to release valve from inlet manifold

10 Note that the metal pipe from the valve to the manifold itself should not be disturbed - it is not available separately from the manifold.

However, check whenever the manifold is removed that the pipes end fitting is securely fastened (see illustration).

6.10 Check end fitting of EGR pipe into inlet manifold whenever manifold is
6.10 Check end fitting of EGR pipe into inlet manifold whenever manifold is removed, but do not disturb

11 Check the valve for sticking and heavy carbon deposits. If such is found, clean the valve or renew it.

12 Refitting is the reverse of the removal procedure. Apply a smear of anti-seize compound to the sleeve nut threads, fit a new gasket, and tighten the valve bolts to the specified torque wrench setting.

EGR pipe
13 Disconnect the battery negative (earth) lead - see Section 1 of Chapter 5.

14 Remove the air mass meter and resonator - refer to Chapter 4.

15 Unbolt the exhaust manifold heat shield and remove both parts, or move them aside as required to reach the end of the EGR pipe.

Unscrew the sleeve nut securing the pipe to the exhaust manifold (see illustration).

6.15 Unbolt exhaust manifold heat shield, and unscrew sleeve nut (arrowed)
6.15 Unbolt exhaust manifold heat shield, and unscrew sleeve nut (arrowed) securing EGR pipe to exhaust manifold . . .

16 Undo the two screws securing the pipe to the ignition coil bracket, then disconnect the two vacuum hoses - note that these are of different sizes, to ensure that they cannot be mixed up on reconnection. Unscrew the sleeve nut securing the EGR pipe to the valve (see illustration). Withdraw the pipe.

6.16 . . . undo screws A and sleeve nut B, then disconnect hoses
6.16 . . . undo screws A and sleeve nut B, then disconnect hoses C - note different sizes - to release EGR pipe

17 Check the condition of both hoses, and renew them if necessary (see Chapter 1). Note that if the exhaust gases have been backfiring excessively - eg, due to a blocked exhaust system - both hoses must be renewed, and their connections on the pipe must be cleaned thoroughly.

18 Refitting is the reverse of the removal procedure; ensure that the hoses are securely connected to the correct unions. Apply a smear of anti-seize compound to the sleeve nut threads, tighten the nuts securely, and tighten the two screws to their specified torque wrench setting.

EGR exhaust gas pressure differential sensor
19 Refer to Section 4 of this Chapter.

EGR solenoid valve
Note: This component can be identified by its larger top and its two fastening screws. Do not confuse it with the adjacent pulse-air solenoid valve, especially when reconnecting vacuum hoses.

20 Disconnect the battery negative (earth) lead - see Section 1 of Chapter 5.

21 Remove the air mass meter and resonator - refer to Chapter 4. If better access is required, remove the plenum chamber also (see illustration).

6.21 EGR solenoid valve A and EGR exhaust gas pressure differential
6.21 EGR solenoid valve A and EGR exhaust gas pressure differential sensor B, located on bulkhead mounting bracket

22 Releasing its wire clip, unplug the electrical connector from the valve. Remove the two retaining screws, and withdraw the valve from the bulkhead mounting bracket, then label and disconnect the two vacuum hoses.

23 Refitting is the reverse of the removal procedure; ensure that the hoses are correctly reconnected.


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