hello... I'm new to the forum.. I have an 1986 jaguar xjs V12.. purchased last summer for 1800.00. ran okay.. changed valve cover gaskets wires plugs cleaned top end best as possible, fixed variuos wires and sensors... car ran smooth and fired right up... as summer progressed into fall and temps changed, mid 40's to 50's The jag started to run as if it was running out of gas..... then it would run smooth....... a co-worker would follow Me to work and stated it smellled like lots of raw gas.... car ran rough and smooth for about a month, always starting..... then one morning it started and stopped almost instantly.. turns over almost seems to want to fire... I can smell gas and hear pump running....




hope You can help...Doug...

 

My first thought, what with the raw gas smell....which occured even when the engine ran...is excessive fuel pressure. A fuel pressure test would confirm that...although performing one is a PITA as you have to cut open a fuel line and "T" into it for your f/p gauge.

Spark plugs wet with fuel might confirm a fuel pressure problem....although with repeated cranking events they might end up wet anyway. If you pull a couple plugs you might as well check for spark while you're at it....as that always goes along with diagnosing a no-start situation anyway.

There are numerous possibilities but you gotta begin somewhere so I'd go with pulling a couple plugs to see how they look and checking for spark. We'll go from there.

Cheers
DD

 

There could be multiple causes for this. Fuel pressure does sound likely, but (this may be due to my lack of knowledge in jaguar V12s) but it also sounds like a Crank sensor issue?

 

Good thinking on the crank sensor idea but, in this case, not applicable. An '86 doesn't use the crank sensors.

Just FTR, the V12 XJS used crank sensors when fitted with the Marelli ignition which was used beginning with at VIN 156xxx, roughly. In USA-speak ths translates to mid-'89 model year.


Cheers
DD

 

Hey guys thanks for advice.. I have discovered that the fuel pump does not ever turn off like most pumps after pressurizing the system, correct? Also it is pumping loads of fuel into the engine. I took off an air cleaner assy. and opened the throttle and gas poured out, it did it on both sides, pressure regulator? the car was hit on the right side rear to the point of 1/4 replacement , all wires and relays on that side are questionable. My neighbor is telling Me to put a 350 v8 in it, I would rather run the v12......thanks again...Doug

 

i have a complete set of jaguar dealer service manuals 4 book set. it's a confusing set of books.... trying to determine what relay does what in the in the trunk is hard even with the books and schematics.

 

I noticed that the fuel temp sensor has been super glued, will an inoperable temp sensor mess things up?

 

good spark and turns over... loads of fuel pumped into engine leaking out at the cat. converters..fuel injectors? pressure reg.? please help Thanks Doug