You can search for one anywhere. Like Kirby showed, plenty of aluminum (and plastic, avoid!) I chose to buy this brass one made in USA.
I agree the the check-valve thing is worth considering and/or trying. Certainly can’t hurt.
But a fuel pump in good condition should recharge the fuel system in about 3 seconds or so. If you’re having extended cranking lasting longer than that I’m not so sure that fuel drain-back is the problem.
Cheers
DD
I believe that the problem is that the evaporated fuel vapor has nowhere to go; because of the fuel rail being an oval, fresh fuel cannot purge the vapor from the entire rail through the B bank regulator because of more than one exit path. I think it would purge correctly if that front crossover were closed off- perhaps by a valve that would open when the engine was running.
My guess is that the A bank regulator is supposed to work in conjunction with the fuel pump check valve to maintain approx. 60psi in the filter and line leading to the A bank regulator. As the fuel expands and vaporizes, both in the rail and the filter/line, the B bank bleeds off pressure in excess of the 2.5 bar. The pressure in the line/filter replenishes it, which is why the fuel pump check valve is important, and why there is an A bank regulator.
A simple fix (in my humble opinion) would be to retain the fuel pump check valve, do away with the A bank regulator and the crossover on the rail- this would force the vapor to purge from the entire rail through the B bank regulator.
Robert, That was my thought process 30 years ago, and it still makes sense today. My fuel rail was blocked off at the necessary points to force fuel through one path back to the tank. Although it improved, this modification did not cure the hot start problems. Inherently the design of the fuel rails, both pre and HE models are flawed. In the preHE models the small diameter and long meandering design results in a rail that absorbs and traps engine heat. Add to that are the various fuel paths back to the fuel tank that bypasses entire injectors and it’s easy to understand why, in a hot start condition problems occur.
The Later cars have an improved fuel rail design, but the design defies logic by not bring the fuel in at the very front of the rail and exiting the fuel at the end of the rail. In addition, the front two injectors by design cannot be cleared of any fuel vapor once the fuel pump is energized . The most important issue is to keep the fail pressurized. Pressure is maintained in the rail by the check valve in the fuel pump and the second FPR. If the check valve at the pump is missing or defective, or the second FPR is defective, then the car will have hot start problems. Personally, I would remove the first FPR, IMHO it has no real purpose and could be a problem if it malfunctions. Diagnosis starts with a leak down test of the rail. If I remember correctly, pressure should hold for 20 to 30 minutes. If that test passes, then move on to testing the second FPR for vacuum activated pressure hold increase and then I believe the later cars also had a thermal device on the rail.
Apologies for the long post.
Yes, I had read your construction of a new fuel rail with much interest (in fact I have read ALL of them with much interest) and agree heat is the problem; unfortunately not much can be done about it. Mine is a HE and has the vacuum switch in the line to the B bank regulator- this vacuum switch would only help when the engine is running, as there is no vacuum when off. Fuel today has a lower vapor point which aggravates the problem. I think that the ultimate cure would be a single path rail operating at a higher pressure. I have measured the rail pressure on mine when the problem occurs and it is at the regulator set point 38 psi. Problem is that it is 38 psi of vapor. Mine will hold this pressure for a hour or more. I have never checked the supply line pressure to see if the fuel pump check valve has failed. A summer problem for the most part, although it was 44 F here yesterday and it was rough on a hot restart.
What the fuel system needs is a method to bleed off the vapor, rather than have to wait for the vapor to cool and return to a liquid state. If you could devise an auxiliary switch to energize the injectors for say 5 seconds, holding them all open, and repeat maybe 3 times, with a short interval in between to allow them to cool a bit. Thus purging the vapor into the intake manifolds. Just a random thought. SD Faircloth
I thought of something similar, but might try a simpler fix- put the A bank regulator (3.5 bar/50 psi) in place of the B bank regulator (2.5bar/36psi), then fab an elbow in place of the A bank regulator. The increase from 2.5 bar to 3.5 bar is 40%, but results in a less than 20% increase in injector flow, which the ECU software should be able to handle (2.5ms to 2.1ms pulse duration). The 50 psi pressure in the rail might be enough to reduce vaporization during hot soak, and the modification would be reversible.
I think we’d all agree that if the rail was full of liquid fuel and the FPR was maintaining rail pressure as it should, hot starts wouldn’t be a problem. If we presume that some of the fuel in the rail is vaporizing due to heat soak after a hot shutdown, how is that causing the issue? I could see the argument that the pre-H.E. racetrack rails were too thin and easily got heated, but OTOH such skinny rails should allow the vapor to be pushed through quickly. Big fat rails would take more heat before vaporizing the fuel, so is the idea to make the rails so large that they can absorb heat until the heat soak is past without vaporizing any fuel? Or is it that the fuel vapor can rise to the top of the passage while liquid fuel flows through underneath and to the injectors?
Frankly, I find all of these arguments unconvincing. Here’s what I believe is a more plausible explanation: Fuel in the rail is vaporizing, and upon starting this vapor is pushed downstream into the B-bank FPR. The FPR is just dandy at controlling pressure in liquid fuel but fails miserably when there is vapor flowing through it. Basically the vapor goes pffffft through the FPR, leaving the rail unpressurized until the fuel pump can catch up with the flow. And Jaguar’s fix of cutting off the vacuum to that FPR does just what you’d expect, bumping up the pressure in the rail a bit to compensate for it being waaaay low.
If this hypothesis holds water, what can be done? In general, one would either need to prevent fuel vaporization or improve how the B-bank FPR deals with vapor. I dunno if there are better FPR’s available that will hold pressure with either liquid or vapor flowing through them. Or perhaps the fuel cooler could be installed before the FPR rather than after it. Of course, I’m not sure the A/C system will come on line quickly enough to address the problem.
Now, just to cause trouble, I’ll suggest another plausible explanation: Fuel in the rail is vaporizing, taking up a lot of volume in there. The FPR works just fine with liquid or vapor. But when the car is started, a bunch of vapor in the rail itself, over the valley, is pushed into the line toward the B-bank FPR. This line, not being over the valley, is much cooler. Suddenly, all that vapor condenses into liquid. The resulting decrease in fuel volume leaves the rail unpressurized until the fuel pump can catch up. And this can go on continuously, as fuel in the hot rail continues to vaporize and then condense as it exits the rail and approaches the FPR.
I have often wondered if this fuel circuit would benefit from some sort of accumulator installed in the supply line. Basically something that would help maintain rail pressure when the fuel pump isn’t keeping up. Really, a container with air in it would work; the air could compress and expand as necessary to hold the fuel pressure steady. In fact, the fuel filter might serve such a purpose as long as its outlet isn’t pointing upward. Mounted on its side, the upper half might maintain a volume of air and help absorb pressure fluctuations in the fuel line.
These all sound plausible, but quite complicated to solve.
How about preventing the vapor in the first place?
One idea is some simple 12V fan with a relay that stays on for 20 minutes after shutdown, not drawing too much amperage of course, that moves the heat rising from the engine, so that the fuel rail does not cook. Dave’s vents in the hood seem to do the trick.
We have two V12 Jaguars that are driven regularly, a 1990 XJ-S convertible (5.3L V12 w/ Marelli ignition) and a 1990 V12 Vanden Plas (5.3L V12 w/ Lucas ignition). The V12 VdP has an operational climate control system and I never experience a hot restart issue with it. The climate control system components are all present in the XJ-S convertible but the A/C does not currently work. I occasionally experience the hot restart problem in the XJ-S. I recently tested both EAC5086 thermal vacuum valves and they both work great.
So it appears that with my cars there might be a coorelation with the A/C system. I plan to get the XJ-S A/C system working this spring and that might tell us something. Right now the excess fuel returning to the tanks in the V12 VdP is cooled by the fuel cooler but it is not in the XJ-S.
Does anyone with a fully operational A/C system experience the hot restart problem? Is it possible that the fuel cooler is important in minimizing the hot restart problems because it cools the fuel enough to help avoid vapor lock?
Paul
Yes, my a/c is fully operational and I notice the issue on any hot soak restart, pretty much any ambient above 50F, after driving on the freeway for an hour. After run fan works, usually only if the ambient is above 85F
That said, I have not checked the fuel pump check valve. My rail pressure holds at 38psi for over a hour.
Hi Paul-
Yes. My AC works perfectly and I have an obnoxious hot start problem. I will be installing an additional FP gauge and doing some tests in the coming weeks in an effort to provide some objective data, will report results. This has been an issue for me for a long time, but with the auto trans it was easy to feather the throttle for a minute or less while the idle stabilized between 500-1000. With the manual trans it’s worse, the idle surges badly from 0 to 1500, can stabilize with throttle at 1500-2000 but must do so for 30 secs, then it’s fine. It’s hard to look good in your v12 Jaguar when it misbehaves.
I don’t see how this would matter… the consensus seems to be that the fuel is vaporizing in the rail, and the fuel cooler comes after the rail. The freshly cooled fuel would have to go all the way to the tank then back up to the rail to have any impact, And I don’t see the fuel cooler doing much during crank / the first few seconds of startup. My .02.
Regards
Bob
Robert, curious if you’ve ever watched the rail pressure during the hot start? Wondering if it fluctuates at all.
Regards
Bob
I have, not a lot about 2-3 psi until it clears. I will probably tee a gauge tap into the line from the pump to see if that holds pressure when its a little warmer out.
As a test, what about cracking the hood (not fully open) next time you park for 30 minutes and see if that helps.
I do that every time, doesn’t seem to make much difference. I haven’t tried it fully open, I’ll do that the next time I put it in the garage.
Now i remember what i changed and the hot starts got a bit worse. Went from 180F to 190F thermostats. I have seen 20F coolant rises in 20-30 minutes after shutdown. 200F vs 210F make that much difference to fuel?
(RGK says “Mine will hold this pressure for an hour or more.”
Robert, since your rail holds pressure for an hour, then the check valve and second FPR are working properly.
I can’t comment on the HE models but on my Pre-HE none of the following solved the issue.
Modified rail to force fuel in one direction. (Impossible with the small dual rails) / Check valve at the fuel pump and second redundant check valve in the engine compartment. / Modified small electric fan to run on after engine shutdown / saying special prayers.
My conclusion: The rail design was fatally flawed. What I needed was a design that did not collect as much engine heat and cleared the fuel rail of vapors as soon as the fuel pump was energized when the start key was turned on. As you have noted, complicating this problem is that fuel composition has changed since these cars were manufactured. Todays fuel is much more volatile, therefore more subject to vaporizing than ever before. I finally cured my hot start issues my fabricating a new fuel rail. The design is self-purging, a design I believe that Jaguar should have entertained in the first place. If this is a bridge too far then I would recommend the following.
If the rail holds pressure and the FPR’s and thermal switch are working properly, and you still have a hot start problem I would suggest two modifications.
- Wire a timer into the electric fan to run for 20 to 30 minutes after shutdown.
- Wire another timer to the fuel pump to run for 15 minutes after shutdown. (This duration could be adjusted with real world feedback)
Tried that is hot weather without noticeable difference; had to have hood open to use the fuel pressure gauge.