Engine turns but doesn't start

[DavidCabriolet]

Hi, 1986 3.6 manual XJ-SC Engine running fine after a trip, turned off and then attempted to start. The engine cranks over with plenty of gusto. Fuel pump whirs when ignition switched on, plugs clean and dry, fuel half a tank of 98E5 couple of weeks old.
Any ideas as to why it wont now start most welcome.
David.

[poprivet]

I'm not very familiar with the early 3.6 in which the fuel and ignition systems are more like the V12 but if the plugs are dry it would seem likely that something electrical is stopping the injectors firing?

One thing that springs to mind is the ingition amplifier, but it would need more diagnostic work. If you have the service workshop manual there is a decent section on testing.

[JimMann]

Isn't there an inertia switch on the XJ-S that cuts the fuel supply? I believe it used to be somewhere in the passenger footwell on RHD cars. It could be that this has been activated inadvertently, or is failing.

Jim Mann

[steve_m]

As far as I recall the inertia switch cuts the supply to the fuel pump and that appears to be running.
If the pump is running but the plugs are dry it possibly means a blockage somewhere; the usual culprit is the swirl pot at the base of the tank or the pump is whirring but not pumping anything.
If fuel is getting to the engine then I would go for either the temperature sensor or crank position sensor; I've had all of those go on me before.

[DavidCabriolet]

Many thanks for suggestions and will follow these up. Have changed the distributer cap and rotor as well as the spark plugs, cleaned the terminals on the amplifier. Engine coughed but wouldn't catch, as I have a new fuel filter I shall fit that next. I am also waiting for a call back from an auto electrician, since I'm completely lost when it comes to electrics.
Will post an update when anything of interest is discovered.

[andypryce]

Easy to check if you are getting a spark, remove fuse for fuel filter, take out one plug, attach it to its lead and rest it on the crankcase. Get a willing assistant to turn the engine over and you will see the spark on the plug. Best done in a garage as can be difficult to see if sunny….

[andypryce]

And make sure fuel pump disabled or you might get a fire….!

[andypryce]

And try not to touch it as can get a hefty shock, as I can testify….

[DavidCabriolet]

Results are:
Changed plugs, distributer cap and rotor. Cleaned earth to ignition amplifier and adjacent terminals. re seated new rotor as I had made a hash of fitting it the first time. Thought it was a stiff fit, but what do I know as an amateur?
Engine starts fine now.
Thanks for all the suggestions.
David.

[andypryce]

Good job, well done.