Jaguar Repair: 1984 XJ6 Vanden Plas, crank pulley, vanden plas

Question
HELP!  My jag is giving me about 8 MI. to the gallon and it idles very rough....where do I start?  how do I check timing?  could it be vacuum related?  please advise...!

Thanks!

Answer
Hi Mario,
Poor fuel mileage and rough running can be caused by a thousand things so you need to do some testing.
Yes, timing is one of them and needs to be checked with a timing light on either #1 or #6 cylinder. The timing marks are on the front crank pulley seen on the left side. The timing specs are usually printed under the hood. The specs under the hood over ride what any manual says.
You also need to test the fuel pressure at the fuel rail. (about 32 PSI and with the vacuum removed from the regulator it should go up to about 42 PSI)
A cylinder kill test is necessary too, but you must not do it by pulling plug wires on this car as there is a danger of a spark jumping down the coil tower to the primary and damaging the ignition system. You need to find some shop with a scope to do the cylinder kill test. A scope can test your whole ignition system even the plugs.
You should also do a compression test on all cylinders.
These are the tests we had to run in the dealerships when we received such a complaint.
I would like to tell you to go turn a magic screw but that is just not the case.
Howard