Plugs and leads

David Haggas 16 years ago

I am assured by a reputable trade supplier that Bosch Super plus yttrium WR9D+ spark plugs are correct for my 2000 4.0 Range Rover. The web site carsparkplugs.com also throws these up amongst others for the "99-02 Range Rover 2", but their cross reference to the Champion RC11PYPB4 (type shown in owners manual) is a Denso KJ16CRL11 with a gap of

1.1mm. The recommended gap in the owners manual is 0.95-1.05mm. The Bosch ones are
0.8mm! Why this difference in spec? Is this a deliberate ploy to confuse the consumer? Should I stick rigidly to the Champion RC11PYPB4?

I have a drop in power and rough running under 2000rpm. I have replaced the leads and the problem is improved but still not as it should be so I suspect plugs.

Any advice on the plugs to use (or not to use) on this engine appreciated.

David.

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EMB 16 years ago

The 4 on the end of the Champion part number refers to a gap of 0.040" which when deling with spark plugs is generally metricated as 1.1mm. The only plug that seems wrong is the Bosch, although my chart shows it as having a 1.1mm gap.

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David Haggas 16 years ago

On the side of the Bosch box for each plug it shows a diagram showing 0.8mm which caught my attention. Although the retailer put my registration number into his system should I trust it to be correct? There seems to be a difference between the 94-98 RR and the 99-02 for both plugs and leads but he said mine showed up correctly as 2000 model year. If the Champion is

1.1mm that falls outside the 0.95-1.05 in the manual yet RC11PYPB4 is the OEM type!

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