Inlet manifold - removal and refitting

In-car engine repair procedures / Inlet manifold - removal and refitting

Warning: Petrol is extremely flammable, so take extra precautions when disconnecting any part of the fuel system. Don’t smoke, or allow naked flames or bare light bulbs in or near the work area. Don’t work in a garage where a natural gas appliance (such as a clothes dryer or water heater) is installed. If you spill petrol on your skin, rinse it off immediately. Have a fire extinguisher rated for petrol fires handy, and know how to use it.

Removal
1 Park the vehicle on firm, level ground, apply the handbrake firmly, and slacken the nuts securing the right-hand front roadwheel.

2 Relieve the fuel system pressure (see Chapter 4).

3 Disconnect the battery negative (earth) lead - see Chapter 5, Section 1.

4 Unplugging the two electrical connectors and disconnecting the vacuum hose (where fitted), remove the air cleaner assembly cover with the air mass meter, the resonator and the plenum chamber (see Chapter 4).

5 Disconnect the accelerator cable from the throttle linkage as described in Chapter 4 - where fitted, disconnect also the cruise control actuator cable (see Chapter 12).

6 Disconnect the crankcase breather hose from the cylinder head cover union.

7 Unbolt the upper part of the exhaust manifold heat shield; unclip the coolant hose to allow it to be withdrawn. Slacken the sleeve nut securing the EGR pipe to the manifold, remove the two screws securing the pipe to the ignition coil bracket, then unscrew the sleeve nut securing the pipe to the EGR valve - see Chapter 6 for full details if required.

8 Remove the two screws securing the wiring “rail” to the top of the manifold - this is simply so that it can be moved as required to reach the manifold bolts. Unplug their electrical connectors to disconnect the camshaft position sensor and the coolant temperature sensor, then unclip the wiring from the ignition coil bracket, and secure it to the manifold.

9 Remove the three screws securing the wiring “rail” to the rear of the manifold.

Releasing its wire clip, unplug the large electrical connector (next to the fuel pressure regulator) to disconnect the wiring of the manifold components from the engine wiring loom.

10 Marking or labelling them as they are unplugged, disconnect the vacuum hoses as follows:
(a) One from the rear of the throttle housing (only the one hose - there is no need to disconnect the second hose running to the fuel pressure regulator).

(b) One from the union on the manifold’s lefthand end.

(c) The braking system vacuum servo unit hose (see Chapter 9 for details).

(d) One from the Exhaust Gas Recirculation (EGR) valve.

11 Equalise the pressure in the fuel tank by removing the filler cap, then undo the fuel feed and return lines connecting the engine to the chassis (see Chapter 4). Plug or cap all open fittings.

12 Unbolt the power steering high-pressure pipe and the earth lead from the cylinder head rear support plate/engine lifting eye, then unscrew the bolt securing the support plate/lifting eye to the alternator mounting bracket.

13 Unscrew the six nuts securing the engine/transmission right-hand mounting bracket, then withdraw the bracket.

14 Remove the alternator (see Chapter 5).

15 Unbolt the alternator mounting bracket from the rear of the cylinder block and withdraw it, together with the cylinder head rear support plate/engine lifting eye (see illustration).

6.15 Alternator mounting bracket must be unbolted from rear of cylinder block to permit access to inlet manifold nut

16 Unscrew the bolts and nuts securing the manifold to the cylinder head and withdraw it (see illustration). Take care not to damage vulnerable components such as the EGR pipe and valve as the manifold assembly is manoeuvred out of the engine compartment.

6.16 Withdrawing inlet manifold - take care not to damage delicate components

Refitting
17 Refitting is the reverse of the removal procedure, noting the following points: (a) When using a scraper and solvent to remove all traces of old gasket material and sealant from the manifold and cylinder head, be careful to ensure that you do not scratch or damage the material of either; the cylinder head is of aluminium alloy, while the manifold is a plastics moulding - any solvents used must be suitable for this application. If the gasket was leaking, have the mating surfaces checked for warpage at an automotive machine shop. While it may be possible to have the cylinder head gasket surface skimmed if necessary, to remove any distortion, the manifold must be renewed if it is found to be warped, cracked - check with special care around the mounting points for components such as the idle speed control valve and EGR pipe - or otherwise faulty.

(b) Provided the relevant mating surfaces are clean and flat, a new gasket will be sufficient to ensure the joint is gas-tight.

Do not use any kind of silicone-based sealant on any part of the fuel system or inlet manifold.

(c) Fit a new gasket, then locate the manifold on the head and install the nuts and bolts (see illustration).

6.17A Always renew inlet manifold gasket - do not rely on sealants

(d) Tighten the nuts/bolts in three or four equal steps to the torque listed in this Chapter’s Specifications. Work from the centre outwards, to avoid warping the manifold.

(e) Refit the remaining parts in the reverse order of removal - tighten all fasteners to the torque wrench settings specified.

(f) When reassembling the engine/transmission right-hand mounting, renew the self-locking nuts, and do not allow the mounting to twist as the middle two of the bracket’s six nuts are tightened.

(g) Before starting the engine, check the accelerator cable for correct adjustment and the throttle linkage for smooth operation.

(h) When the engine is fully warmed up, check for signs of fuel, intake and/or vacuum leaks (see illustration).

6.17B Check all disturbed components - braking system vacuum servo unit hose (arrowed) shown here - for leaks on reassembly

(i) Road test the vehicle, and check for proper operation of all disturbed components.