Question about 1991 Jaguar XJ6

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1991 XJ6 cylinders 5/6 not firing

New plugs and wires. Fuel injectors appear fine (both electrical and fuel flow). No noticable problems. Running remarkably well on cylinders 1-4, but would rather have full use of all!

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  • schuehle97 Oct 26, 2008

    Had tried th espark plug previously, successfully. Checked compression and have 30 PSI on 5 and 6 (1 - 4 are all 150 - 160 psi). Put some oil on top and they only came up to 40 psi. Suspecting head gasket between cylinders 5 and 6 ~ any other possibilities you can think of? As long as I've got to take th ehead off should I go ahead and do the rings anyway, or anything else?

    PS. 103,000 miles and gorgeous other than the cylinders (could be why it was only a couple of hundred dollars, but still reasonable to me!).

    Thanks very much for the advice.



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Check for spark at the cylinders you mention. Unplug the wires from the spark plugs, put a spark plug in the end of the wires, and attach the body of the plugs to earth, or an exposed metal part of the engine. With the engine running, you should have spark at the plugs. If no spark, get the ignition system tested. If there is spark present, and you think the fuel is ok, then the compression must be at fault. The things that are required for combustion are: spark, fuel, and compression. Get a compression test done on the engine, but first check for any vacuum leaks in the inlet manifold around the cyl 5 and 6 area.

Posted on Oct 26, 2008

  • Mark Stuart
    Mark Stuart Oct 26, 2008

    I think your idea of it being the cylinder head gasket is the most likely, although if there is no obvious fault with it when you remove the head I would definitely get the head checked over, make sure the valves are in good condition and sealing properly. Good luck!



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