I've had about two months of carefree driving since the last visit to my mechanic to replace the octopus hose.
I was driving it a good bit today, lots of stop and go in a 91 degree day, first time I have heard the fan cut on when I parked for a quick errand. Didn't think much about it, but did notice.
Got to my studio, parked for about an hour, went out to move car, started it up put in gear and it cut off. Started it again and it struggled to run, turned it off. Started it again, and all was fine.
Two hours later, I drove it home and fine as always.
No codes, no warning lights, nothing.
Ay ideas?

Fuel vaporlock?

Good idea. It was like it was struggling to get gas.

Makes me think of the fuel pump, or connections to the pump.
Steve

As it was an isolated incident and it ran OK after a restart, I'd go with Vapour Lock rather than Fuel Pump.

Any repetitions could be an early warning of pump trouble.

Graham

What would cause the fuel vapor lock? And is there anything I can do in th future to avoid it.
On my former XJS, this was a sign of possible major and dangerous issues. To the point of fuel smells filling the cabin. I had these problems with mine.

Further more, what's involved in replacing the fuel pump or hoses on the XK8. Again, it was a major undertaking on the XJS, and expensive.

Above is a video of fuel pump replacement from Reverend Sam. I just did the job. Protect the wires, REMOVE the battery, and take your time. It is not a highly technical job from my perspective. Just takes patience and good safety practices.

Below is a write up from Gus's site. I made the tool Sam shows and used it in addition to the little plastic discs that are described in Gus' to get my (2) fuel lines off.

JagRepair.com - Jaguar Repair Information Resource

Vapour lock isn't something that bothers us in northern Europe and I'd never come across it until we were touring along the south coast of Spain in June.

Coming back to the car which had been parked out in 95 deg temperatures, it would barely run with almost no acceleration. Stopped but couldn't find anything that was obviously wrong with it. Restarted and let it idle until it was running evenly again. At the time I put it down to a combination of temperature and the 10% Ethanol 95 octane fuel I'd been using. The tank was down to around one quarter so I filled up with 98 octane and it never happened again while we were down there or on the return journey home.

I'll be interested to hear if this is a regular issue for members who live in hot climates.

As for replacing the fuel pump, Jacsun has given a comprehensive and concise summary in post #7 with the important links.

Graham

Ah ha! I did something the other day that I read on the forum.
Someone said we could actually use mid grade gas in our cars with no issues so I took a chance and filled up with mid. Now that I think about it, I have noticed a bit of power drop.
I'm about 1/2 tank now so I'll go fill up with premium and hopefully get it back to where it should be.
OR, do I run most of this out and fill up with premium!

I have not experienced vapor lock, nor have any other owners I know here in Georgia. And it does get hot. I have been using mid grade 89 octane 10% ethanol and can not see a significant difference, but I'm not racing anyone up the hills.

I haven't experienced vapor lock here in North Carolina since the days of carburetors in the 1960s and 1970s. 100+ degree days in July and August are common here (though none at all this summer, we've been lucky enough to top out in the mid-90s)....

Fuel pump problems have certainly been known to strike these XK8s. But it seems to me that the cars that are driven regularly tend to hold up better, including the fuel pumps....

Along with your planned premium gas top-up, pour a 20-ounce bottle of Chevron Techron down the hatch. I believe Advance Auto Parts has a buy-one-get-one-free sale on Techron right now....

No such thing as vapor lock in a car with the pump in the tank. Period. Vapor lock occurs on the supply side of a pump. That and keeping the pump cool in the tank are the two main reasons for locating it there.

Vapor lock sounds so much cheaper

A vapor lock is likely to develop when the vehicle is in stop and go traffic due to under hood temperatures. A vapor lock can also develop when the engine is stopped while hot and the vehicle is parked for a short period. (Heat soak) The fuel in the line near the injectors can heat up sufficiently to form a vapor lock. The problem is worse in hot weather. (and black cars)

Catman, I live in a tropical island and my car is black. You made it sound like it's just a matter of when not if for me.

Now I have to ask, where in the world do you guys find 98, and 89 octane fuel? Over here, regular is 87 and premium is 91. Premium used to be 93, but then Texaco called it quits and left the island, and since then, the remaining gas stations have switched to 91 now that the big competition is out. I would love to know if 98 octane makes it go any faster. I might just add an octane booster with my next fill up.

Eh, it sounds like an isolated incident. Vapor lock on modern cars is a pretty unlikely event, but not impossible. Sort of like a 'perfect storm' event. He may have just gotten a number of heat related events building up that day.

I doubt you will get much power from octane boost added to 91 octane fuel. Now if you had an XKR...

I won't pretend to know the details, but our cousins across the pond have a different scale used to measure octane (or maybe it's us colonials that are odd). The high grades are likely the same, as are the low grades.

I agree with notion that systems with pumps that suck are more likely to suffer the condition, but that doesn't rule it out completely on our cars.

I mentioned fuel pump as culprit only because my car suffered similar non run events before it died, and I considered the vapor lock possibility to be remote. But you never know, these cars are full of surprises!

All the best,
Steve

Don't know if this is classic vapor lock, but yesterday, after driving about the same as the day before with the heat and stop and go driving when I had the issue, I stopped to fill up with premium fuel. And the minute I unscrewed the cap, a suction sound happened. It's only happened one other time since I had it. But we've only had a couple above 90 degree days and I usually don't drive it those days.
I also noticed a little before I filled up, it wasn't driving full force. But once I filled up, it was totally normal! Go figure.

On systems with recirculating in-tank pumps there is a possibility of a failing pump having problems exacerbated by heat picked up while in the underhood area and returned to the tank. However, your reporting of hearing a 'suction sound' would be indicative of a problem with the vapor recovery system or fuel cap. As the pump empties the tank air is need to replace that void. If air cannot enter the tank the pump will work until its suction limitations are exceeded. If the issue recurs try removing the fuel cap and see if it starts soon after.

I'm pretty sure this was the issue. Once I filled tank and restarted, it ran fine. My cap is a bit manky and it seems to twist too tightly. Sometimes it won't click but over tighten I guess.