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2.1 - Cam Cover and Gasket ( Paul Stow,  December 1, 2001 )

An aging cam cover gasket may begin to seep oil, particularly around the cover bolt holes. The circular spark plug hole seals may also begin to weep, causing a build up of oil around one or more spark plugs. It is also necessary to remove the cam

cover when checking valve clearances and though this is not a frequent service item it is worth doing whenever the cover is removed.

To remove the cam cover, it is first necessary to remove the middle top section, by undoing the three torx bolts. Unbolt the epoxy encased ignition coils from the top of each plug and pull upward to free them from the spark plug.

Note how the wiring to each coil is of the correct length, and also note the arrangement of the wiring for the rearmost plug. Unclip the wiring and move the coils carefully out of the way. Also undo the clip and disconnect the breather hose from the right hand side of the cover.

The cam cover can be now removed by undoing the series of bolts around it's edge and lifting gently upwards. A little effort may be needed at first to break the seal.

If you are replacing either the cover gasket or a plug hole seal, it's worth doing all the plug seals and cover gasket at the same time. Also check the valve clearances following the procedure given below.

Seat the seals and gasket on the top cover prior to replacement. If necessary, use a little engine oil to help them stay in place. Make sure the gasket is aligned correctly, particularly around the halfmoon sections at the back of the head.

Replace the cover and gently tighten the bolts. Although precise torque and tightening procedure aren't critical here, follow good practice by starting with the left and right side bolts in the centre and working in diagonals to the ends.

Refit the wiring to the coils and then reattach the coils to the plugs. As with a normal HT lead, they may need a good push to click into place. Now gently tighten the coil fixing bolts - they don't need to be much more than finger tight, but there's no need to be afraid of them either. Refit the top centre cover and you're done.

2.10 - Oil system ( )

2.10.1 - Oil and Filter Change ( Paul Stow,  December 10, 2001 )

Warm the engine through to thin the oil and ensure any particles are not sitting in the bottom of the sump.

Raise the car to gain access and, after placing a suitable container underneath, undo the sump drain bolt at the rear of the sump. When the flow has stopped, clean the bolt, copper washer and mating surface on the sump, and refit. It needs to be snug but not overtight. Leaks are usually cured by fitting a new washer.

Use a strap wrench or similar tool to undo the oil filter. Be aware the filter will contain oil, so keep your container underneath. Clean the mating surface on the engine block and use a finger to spread a thin layer of oil over the rubber sealing ring of the new filter.

Screw on the new filter until snug, then tighten approximately a further quarter turn. Hand pressure is normally adequate for this, but if you do decide to use a strap wrench, fit it close to the base of the filter such that you do not deform or damage it in any way.

Good oil filters feature an anti drain back valve which prevents oil draining back into the sump whilst the engine is stopped and therefore provides quicker lubrication when the engine is started. The valve can normally be seen as a piece of plastic behind the holes in the base of the filter. Jaguar and Fram filters are known to have this valve.

2.10.2 - Oil Cooler Bypass ( Paul Stow,  December 10, 2002 )

Some markets require a separate oil cooler to be fitted, the feed for which comes from the block beneath the oil filter. Where an oil cooler is not required, a bypass is fitted, consisting of a small 180 degree steel hoop-shaped pipe, again fitted next to the oil filter.

The connection is sealed by small rubber O-rings which do fail over time and produce an oil leak.

Replacement requires only unbolting and removal of the bypass pipe to gain access.

2.10.3 - Oil Pressure Sender ( Paul Stow,  December 10, 2001 )

The sender is located on the side of the engine block, underneath the inlet manifold toward the rear, and can be identified by the large diameter fixing nut. Removal is simple once you have access. On replacement, Jaguar recommend that a thread sealer such as Loctite 562 be applied to the exposed threads once the sensor has been screwed in by a thread.

Early X300's had a true pressure sensor, which is prone to erratic readings as a result of the carbon track of the potentiometer wearing out. Because of this, and customer concern over reduced oil pressure at idle, which is perfectly normal, later X300's and dealer repaired early models had a simple pressure switch fitted instead. This is linked with software reprogramming the instrument pack to cause the needle to sit either at the mid-point, or at zero dependent on the switch.

2.12 - Idle Speed ( Paul Stow,  December 1, 2001 )

The normal hot idle speed is 750 - 800 rpm in Park or Neutral and 650 - 750 rpm in Drive. The speed is determined by the ECU, which drives the Idle Speed Control Valve located in the throttle body, and it is not adjustable. Note the ISCV is a different device from that used on the previous AJ6 engine.

If the idle speed is incorrect and no other problems are apparent, check for a clogged or dirty throttle body, correct operation of the throttle position sensor or a weak throttle return spring.


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