Spark plug change. 4.2 V8

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Spark plug change. 4.2 V8

Postby J44EAG » Mon Nov 16, 2015 6:05 pm

Spark plug change today at 79k miles.

Applies to V8 4.2 Jaguar models with perhaps some engine dressing differences between X350, S-type, XK8 and XF both supercharged and non supercharged variants. With minor differences, the job is not dissimilar to the procedure used on the earlier 4 litre V8 models. 4.2 models have pull off covers which make matters easier than 4 litre cars which tended to have bolt down covers fitted. 7mm spanner needed to release the covers on 4 litre engines.
The procedure is as follows.

Remove the spark plug covers to access the plug on coil packs. 8mm spanner to remove a single lock down bolt on each coil. Press at the back of the electrical connector plug to separate from the coils. This is the press down tag adjacent to where the electrical wires enter the plug. This job can be a frustrating fiddle on the rear two cylinders on both A and B banks as the engine is tucked well back towards the front bulkhead and space is limited.
Gather a variety of 14mm plug sockets, extensions and universal joints. A foot long length of 1/4" bore rubber fuel hose is useful to remove spark plugs from their wells once they have been screwed out of the cylinder heads. Plug changing on the front cylinders is easy enough but the back cylinders are obstructed by various pipes and fittings. On the right hand side bank as you look from the front of the engine to the rear is very obstructed and coil removal is very tight indeed. Tip the top of the rear coil backwards towards the bulkhead to gain removal clearance. On the next cylinder forward, extract the coil upwards through the EVAP pipes and two air con pipes. That is the only way it can be got out. A bit of a nightmare. Difficult but not impossible. Allow a couple of hours for the job.

Plug gaps should be 1mm. At nearly 80k miles the removed plugs had eroded to 1.5mm so were definitely past their prime. A small trace of copper grease on new plug threads helps new plug fitting and is most useful as an anti-seize compound when you next come to change the plugs.
Any difference after the work? Yes, certainly, particularly noticeable on initial throttle pick up away from a standing start. The car is generally a little more lively as a result of the plug change. Worth doing even though misfires were not present. All part of preventative maintenance and increased reliability.

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