If you're content to wait a week, I can pull my lines apart on my 1994 6.0 and see what's there, as the connection looks the same as in your photos. I don't want to do it before a big trip though and have it leak along the way.

I wonder if the old ring is still in the fitting and the new one was fitted on top? Now there are two in there?

 

Grant,
I will have to disagree with you here after taking a look at the rail on my 6.0. The open ends of pipes 1&2 attach to the rail, as the pulsation dampener is clearly visible on hose 2, and that's in the engine bay. I think O rings 9&13 are connected to the lines running to the rear of the car.

 

Ah, you know what, I think Jagboi's right. The weird curve at the end of Hose #2 is the bit where it dips under the aircon compressor. No mention of O-rings at all at that end.
That said, Jagboi, I'm not planning on any major trips immediately, so it would be great to know exactly what's in your hose.

This does, of course, still leave the question of why the hose can still be tightened open. This morning I checked again, and I could tighten it about 1/12 of a turn. It seems to be only after it's been driven, as checking it on Monday after not going anywhere Sunday (after tightening on Sunday am), it was still tight. I should measure the gap to see if it changes, but I'd need a very precise ruler.

 

Not having a later V12, I was following logical Parts Drawing layout.

The spare parts drawings have always shown items in the Left as the nearest the front of the car. Not so in this drawing for some British reason.

AND

I agree, that the strange bent pipe is the one that attaches to the RH front of the fuel rail.

This fuel rail Parts Drawing clearly the correct orientation, shows things as I look at them, front side is to the Left of drawing.

Still NO o/rings for what you are dealing with.

Maybe the seal fitted does NOT belong. All the fuel fittings on the earlier system are male/female tapers, and no issues at all.

 

Very useful tip, that. I've often found the orientation of parts drawings to be a bit confusing.

The green rubber thing in the fitting came with the hose, so I'm at a loss to work out what the oddity is. For what it's worth, today I checked the connection after getting back home, and it was tight, so it will be interesting to see if there is any change in the morning. If there is no visible increase in the gap between the nut and the rail joint, I'm inclined to leave it and not compulsively tighten it each morning, as that doesn't seem like it would actually do much.

 

As long as it doesn't leak, leave it be.

 

Indeed. I just hope that if it does leak, I notice before fuel spurts over the hot engine....
(Then again, I keep reading about how petrol/gasoline doesn't actually burn as easily as shown in movies, and needs a specific ratio of fuel to air. Though a hot engine would vaporize it, it wouldn't provide the heat needed to ignite it, barely being 100C at max. I hope....)

 

Dream on!
SDSD, I would take the joint apart (have it taken apart) and find out, for sure, why it is leaking, and fix the problem. It is not normal to have a fuel line weeping and needing tightening.

 

Wait, let me be clear: the joint is NOT leaking, weeping, dribbling, or in any way not doing its job. There is no imminent danger of petrol getting anywhere. If it were leaking, I would not even think of driving the car anywhere....

I checked it today, and it barely moved. The fact that the nut doesn't reach the fuel rail is odd, but my old one didn't either--though I never tested it for tightness. I'm just wondering what internal mechanism is allowing these small slight turns.

 

Hi Someday

I know we've been down this Road before (no pun intended) although on second thoughts maybe there was!

But even with all those Diagrams and the Photos you took of your Fuel Rail, I am still not convinced, as surely that Green Pipe that comes from the Drivers Side of the Fuel Rail (UK) Spec has to be the Fuel inlet instead of the return pipe

As such it would make perfect sense for the solid metal Green Pipe to be the Fuel Inlet (the high pressure one) as the one thing you don't want is any leakage of High Pressure Fuel in the Engine Compartment

While the Rubber one is the sort that you would maybe expect to find on the Return Pipe and while we're on the Subject where did you get that Part Number from? EBC 4363 the one shown in your Photo with that massive question mark!

That Pipe looks a lot more like CBC 8639 which has been Slated as being a Fuel Return Pipe

As I don't have the same Fuel Rail as you, of course I could be wrong but all the same I think it could be worth a double check

 

Hi OB,

Thanks for your input, as always. According to Jaguar Classic Parts, it's absolutely the fuel feed pipe, and the one that goes under the compressor is absolutely the return hose. Here's their page with labels:
FUEL FILTER AND PIPES-5.3 LITRE

The question mark is because that photo was taken when I was still not sure which pipe was which, but it's definitely the correct part.

 

SDSD
Sorry, I thought you were seeing weeping fuel unions. The fact that the male fuel union nut hexagonal is not against the outer part of the female it screws into is neither here nor there. It is made to seal the fuel by pressing the internal parts together, not to sit flush against the outer. Indeed there has to be a bit of extra thread, or else the thing could run out of thread before the internal sealing parts were tight enough.

 

Okay, that makes perfect sense. So there's no need at all to keep trying to tighten the nut, then? I would probably end up squashing the rubber too much.

That's rather a relief, actually. Odd that the mechanic considered it an issue, however. Or perhaps it's just a case of letting rubber settle in. I don't know - best I don't speculate about things I know nothing about. I just get paranoid, because as soon as one problem gets fixed, another is sure to appear soon.... (Yeah, welcome to Jaguar ownership....)

 

The logic is easy to check. Fuel comes into the rail, to the injectors and the regulator is the last thing the fuel sees before being returned to the tank. Anything upstream of the regulator is the feed, downstream is the return.

 

Not sure this is a matter of pure logic. Without knowing what the regulator does, you would have no idea which way was which in a closed loop system like this. I know I wouldn't have known that "anything upstream of the regulator is the feed, downstream is the return" until half a minute ago. But it's a useful tip for the future, assuming regulators are a standard item on fuel systems.

 

I am back from my trip to the largest all Jaguar show in North America in Victoria, BC and the XJS drove very nicely, a trip of about 2300km. Now that I'm home I opened up the fuel line on my 1994 XJS. It does have an O ring, and to be honest I have never seen this type of connection on a fuel rail before. The nut was not tight, it was easy to turn with a wrench, and it wasn't leaking fuel. I think as long as it's sung, it's fine, any more pressure simply extrudes the O ring out of position. The shoulder of the pipe connection sits against the O ring.

 

Sorry, I assumed too much. The regulator is what sets the pressure in the fuel rail. They are standard industrial devices, used for many things, from gasses to liquids. It works by opening to release excess pressure to a return line ( in this case) and keeps the pressure upstream to the desired pressure. As the pressure falls after the discharge valve opens, a spring closes the valve allowing the pressure to build until the pressure of the oncoming fuel overcomes the spring and opening the discharge valve, releasing the pressure back to the set point. The valve closes and the process repeats. Changing the tension in the spring changes the force needed to close the valve, and thus the set pressure.

If the regulator was before the fuel rail, it would maintain a set pressure between the fuel pump in the tank and the regulator, but the rail and the return line ( if after the regulator) would effectively be zero pressure as the fuel is free to return to the tank. So the fuel comes into the rail from the pump to the injectors, and then to the regulator, and back to the tank. In a way the regulator is holding back pressure into the rail.

 

Your explanation reminds me of when I was visiting the USS Midway in San Diego and a docent was trying to explain about the steam system. I understood the words, but the meaning constantly floated just out of my grasp. I had to ask him to repeat the basic functions about three times, and he must have thought I was a complete imbecile. But in this case, I can re-read it as many times as I like, and you won't even know how dense I am.... And I think after the fourth time, I now understand. (Always assume I can barely tell one end of a car from the other when it comes to that magical apparatus that lives under that big metal hatch I stare out over when driving....)
Thanks very much for that write-up, and especially for checking your own fuel line. Those photos are very helpful. The last couple of times I checked the connection, it was pretty tight (not loosened at all) and so I have just left it for the last week. So far, the engine hasn't exploded in a ball of flame....
If you want to write up a post about the Jaguar meeting and your road trip, I'm sure it would be a very interesting read....

 

Here is an animation of a pressure regulator that while not perfect, might help. The low pressure side ( light blue) is on the return to the tank line in our cars. The low pressure acts on the diaphragm and balances against the spring force on the other side of the diaphragm. The amount of tension in the large spring on the top side sets the desired discharge pressure. Some regulators are adjustable, the ones in our cars are not. The spring force is balanced against the fluid pressure (or fluid force - since pressure is simply force per unit area, and the diaphragm area is fixed). The diaphragm will deflect in whatever direction has the highest force.

There is a pushrod attached to the diaphragm, and a disk valve attached to the lower end of the pushrod. The disk acts to either close off a flow passage, or open it to allow flow.
If the downstream (right side) pressure is high, it acts on the diaphragm and pushes the diaphragm upward against the spring, and in turn that lifts the pushrod and the disk seats across the opening blocking any further fluid flow into the regulator. As the pressure falls ( due to fuel returning to the tank) the pressure on the right (downstream) side drops.

Now the large spring force is greater than the fluid force on the diaphragm, and that pushes the diaphragm downwards, and in turn moves the disk down and opens the flow passage. The fuel pump and injectors are on the left ( upstream) side at higher pressure than the discharge. The high pressure fluid moves into the regulator, acts on the diaphragm and can lift the spring, closing the disk.

In reality, there is a balanced state between the spring force and the fluid force on the diaphragm where the disk valve lifts enough to provide a constant flow at the required pressure, rather than cycling open and closed. It's very similar to a thermostat in that regard, it opens enough to allow coolant into the radiator to maintain a steady temperature. The regulators in our cars are not quite like this, but they function similarly. The physics are the same.

Hopefully this helps you visualize it a bit better?

 

Much better, thanks. Thanks for all the effort you've put into relieving my ignorance, and feel free to vent if I put more pressure on you....
Are you a specialist in this sort of area ("engineering") by training or occupation, or just someone who's studied it to work out what the hell's going wrong with their car? The level of detail makes me wonder if it isn't the former.