Couple of months ago my Jag which has been faultless in the 10
years I have owned it wouldn't start without turning it over
several times and finally reving the engine to about 2000RPM but
would still die if it fell below 1000. Fuel pump diagnosed as the
problem and replaced. Ran ok but not as smoothly as I was used to.
About 6 weeks later problem re-emerged though engine would keep
running but very roughly. Pinching the fuel return line to increase
pressure smoothed the idle so fuel regulator replaced. Ran ok for a
couple of 140km round trips over the subsequent couple of days,
starting without issue. Car was then not driven for a few days and
old problem has come back - will only start after several attempts
and by revving the engine to at least 2000 and holding it there for
a while, though once started it is running fairly smoothly. Did a
couple of short trips and each time had the same difficulty
starting, though the next day it started ok. The faulty starts see
a huge billow of grey smoke from the exhausts which have a black
residue at their outlets. Running it only on 98 octane. I noticed
that the water exit vent in the fuel filler housing had become
blocked and there had been some little water submerging the bottom
of the filler cap, though it was on tight and doubt any water got
in - but I am clutching at straws for a reason and wondered whether
a little water getting into the fuel may have contributed to the
problem. Also, could coil packs be related to this type of thing in
any way? Could it be the ECU? The fact that it started and ran fine for a while and
then, after a few days sitting idle had the old issue again has me
stumped. Normally the car gets driven only on weekends for modest
trips but is always serviced to specification and only a year ago
was quoted by the Jag dealer as one of the best mechanically he'd
seen. Very frustrating - any ideas very gratefully received.

 

The first thing you need to do is address the water in the fuel apperture housing. What you describe sound exactly like water contamination in your fuel. If the quantity of water is not too great, you could try adding some alcohol based dry-gas. Add that to the fuel and drive the car. The alcohol will combine with the water and allow it to be carried through. You'll just have some rough running in the mean time.
I know you probably think the cap would seal out the water.....but it doesn't, it gets in there anyway, new cap or old.
Keep the drain clean!!

 

Thanks. As I said, I had wondered whether water was the problem but had initially discounted it as, when I first discovered the blocked drain hole and fixed it, removing all the water, the car had been running fine post repair and continued to do so for the next few days and couple of hundred kilometres. It was only several days later, when there was no water in the filler receptacle, and the car had been idle that the problem re-emerged. I had also thought water in the fuel would have been indicated while I was driving by intermittent missing but once I eventually got it started and running, it ran pretty smoothly. However I am a novice mechanically so my assumptions may have been wrong. It is with the dealer now for them do have another look over but ironically when I started it earlier this week to take it to them, it started faultlessly and drove smoothly. I thought it was worth letting them run their eye over it anyway. I love this vehicle and it has done less that 80,000kms despite its 15 years and I'd hate to get rid of it but reliability is the key thing for me and the recent expense with it is just giving my wife the ammunition she wants to argue for getting rid of it (a horrible thought!)