Hi guys,

Please delete if not allowed, I've got a 1993 Jaguar XJS 6.0 V12 Coupe with starting and running issues.

The old girl doesn't start on the key most of the time very strong smell of fuel, but if we somehow get her started she runs rough. Unfortunately I don't have much background on this vehicle. Other than when you get 5 miles down the road on a good day it cuts out.

Any idea where to start first on this one

 

Well if it's got fuel then i'd check spark next. Pull plugs and inspect. Distributor too.

 

It might be a coolant temperature sensor, as if that goes open circuit it tells the ECU to provide maximum enrichment for a very cold start. I'm assuming by fuel smell, you mean out the exhaust and it's running rich? Black smoke?

If it's raw fuel with no black smoke, it's possible you have a distributor rotor/cap/ignitor, or coil failure. The ignition system is basically a pair of 6 cylinder systems, and if one fails it will run smoothly on 6 cylinders and not run at all on the other 6. That can lead to a catalytic converter meltdown and plugged exhaust. Check for spark on all cylinders, and when it runs use an IR temperature gun to measure the temperature on both exhaust manifolds to see if they are similar. It's also possible one of the coils is weak and causing weak or no spark on one bank.

 

Does sound like a partial ignition failure. There are two coils. Get a spark tester and verify you are getting spark from both coils reliably while cranking / running. If you are work forwad to the wires and distributor / rotor.

Also quite easy to diagnose becasue when running you will get warm exhaust from the tail pipe of the running side and cool exhaust will be expelled from the side that is malfunctioning. This should be very observable after jusy a few moment of running.

Check the vacuum line to the ECM on the right hand side of the trunk area too. Make sure it has vacuum while the engine is running.

 

Is it new enough to pull diagnostic trouble codes? Those are quite helpful.

 

It has a Marelli ignition. There is a common problem of the rotor burning through. Check it.