Engine Stalls at High Altitude (>10,000 ft.)
 

I have an intermittent fuel fault on my '91 XJ6 sovereign which is pulling my hair out! The problem is the engine fails at high altitude (>10,000 ft) . I have done the following:
1) Changed fuel filter
2) Installed fuel pressure gauge on the fuel rail. OK when cold (~42 psi) but fails (<10 psi) when hot and under full load. Worse when tank is less than half full. From removing the filler cap I have observed that the tank is under negative pressure conditions during failure mode. There is also a gas smell when failure occurs.
3) Changed fuel pump, however problem persists.
4) Blown out both tubes (20 psi air) connecting to the evaporative cap. The tube running to the front appears to be blocked.
I suspect the problem is due to vaporization in the fuel delivery line, possibly due to check valve failure or the charcoal filter is clogged.
Any comments will be much appreciated !
Cheers, Martin

Hi Martin,

I have moved your post to start your own thread since your symptoms are a bit different from those discussed in the other thread from 2009.

First of all, my recollection of visiting Saskatoon is that the elevation was nowhere near 10,000 feet, so I assume you were traveling somewhere west when you discovered your engine stalls above that altitude (above Banff, Lake Louise, Jasper or Morraine Lake, perhaps?).

I don't have a definitive solution for you but I do have some random thoughts:

1. Have you checked for any stored diagnostic trouble codes (DTCs)? If you haven't done it before, let us know and we'll explain it (it's easy).

2. The check valve works in conjunction with the fuel pressure regulator (FPR) to maintain approximately 40 psi in the fuel rail, so if your pressure is falling below 10 psi my first suspect would be the FPR since a new fuel pump should be able to produce enough consistent pressure to overcome a failed check valve. One simple test you can perform is to pull the vacuum hose off of the FPR. Crank the engine and look for wet fuel at the hose fitting, which indicates failure of the diaphragm, which allows unmetered fuel to be inhaled into the intake manifold leading to a rich air-fuel ratio. In combination with the low oxygen concentrations in high altitude air and low fuel pressure, I could definitely understand that your engine would stall.

3. Some sensors can misbehave in cold temperatures, so if you were not only at high altitude but in colder temps, perhaps a coolant temperature sensor (CTS) or crankshaft position sensor (CPS) could have contributed to or caused your stalling.

4. Off the top of my head, I think the tube that runs from the evaporative flange to the front of the car connects to the carbon canister via the pressure control valve or "Rochester valve," which may have been closed when you were attempting to blow out the tube. However, these valves are known to fail, which can allow so much vacuum to develop that the fuel tank partially collapses or "implodes." This is a known problem on some Jaguars but you will have to do some research to see if it applies to your VIN.

5. Aside from the above, you replaced the fuel filter, but how long has it been since you gave the engine a good tuneup (plugs, wires, air filter, distributor cap & rotor, cleaned the MAF and ground points, etc.)? Unusual behavior is often the result of several contributing factors.

Please keep us informed.

Cheers,

Don

Don,

Thanks for this piece of well considered analysis. Pls note that I have corrected my profile as I recently moved to Evergreen, 7,800 ft up in the Colorado foothills. I agree, its hard to find 12k ft roads in SK, or AB for that matter!

Relative to your five points:
1) I have not looked at DTC's since I have no diagnostic error codes showing, However i am interested to do this. Any info will be appreciated.
2) I have checked the FPR in line with my Haynes manual and the procedure: https://www.2carpros.com/articles/ho...-and-regulator. The pressure observations were normal and the system responded correctly upon removal of the vac tube, I saw no sign of fuel leakage/diaphragm failure. Under operating failure mode I observed fuel pressure <10psi
3) The failures did not occur at cold temperatures, in the range 10-15c (~50-60f)
4) I suspect this is the root cause of the failure, namely the tank is not breathing due to check (Rochester) valve failure or blockage in the carbon canister/tubing.
5) The vehicle is very clean under the hood. I recently changed all the filters and inspected the HT cables and coil, although I plan to replace them in the '17 work plan. Under normal operation the car delivers ~24mpg, thus I think general tuneup is an unlikely factor in this case.

I recently ran a bench test on the old fuel pump (using kerosine for safety reasons!) and observed cavitation on delivery when the fuel module is less than half full. Conversely when the fuel module is full the flow is 100% liquid with no air entrainment. I was very surprised to observe the cavitation condition, which represented ~1/4 tank conditions. I repeated the test several times under different flow rates including 42psi delivery conditions with the same observation.

All the failures have occurred when the tank is ~1/4 full, fuel hot, engine under load and at altitude ~12k ft. In all cases I heard severe "shooshing" when removing the gas cap due to pump suction/vacuum. On returning to lower altitude, refilling and allowing the engine to cool the car returns to normal operation. My hypothesis is that fuel is vaporizing in the pump and delivery tubes, hence the system does not work as it is meant to pump in the liquid state as opposed to gaseous state.

I recently disconnected the tube from the gas tank to the carbon canister and diverted it under the vehicle. I ran two successful test runs to the 12k altitude with a full tank of gas, although I have not yet run a 1/4 tank test. Of course there is now no "shooshing".

My next step will be to check out the components as per (4) in your note. This will not happen until next year as I will be away over the winter, I will let you know how I get on. Q: do you know if the carbon canister serviceable, i.e. can the carbon medium be removed and replaced? Finally, is the check valve serviceable, or should I replace it?

Don, thanks again for your insights, very much appreciated.

Cheers, Martin

I know of at least one guy (Groove over on Jaglovers') that has successfully replenished the carbon in the canister - IIRC he just used carbon granules from an aquarium store and sawed the top off the canister and glued it back on to reassemble.

Might be an idea to pick up a used one from the wrecker and have a little practice run though!!

hth

Larry

Hi Martin,

Your hypothesis about fuel vaporizing before the fuel pump is a possibility, as it was a known issue with the earlier '88-'89 cars with the external fuel pumps. Jaguar's solution was to add a second, parallel fuel pump. But your '91 has the pump inside the fuel tank, and I was under the impression that the '90 and later cars did not suffer this fuel vaporization issue.

If I recall correctly, there are actually two check valves. One is at the bottom of the plastic canister in which the fuel pump is mounted, and the other is in the evaporative flange. Neither can be purchased separately from Jaguar, and I think the canister and flange are no longer available either.

I added an inexpensive check valve in the fuel line. The easiest place to mount it is in the inlet line at the fuel rail. I subsequently moved mine to underneath the fuel tank, but I don't think it made much difference if any, so I would put it at the fuel rail. Here are photos showing how I did it:

Welcome to Jag-lovers - Members Photo Viewing Page


Regarding Larry's mention of replacing the charcoal in the canister, Groove's post inspired me to do the same thing. Here are photos:

Welcome to Jag-lovers - Members Photo Viewing Page


Based on my observations inside the carbon canister, I think it is less likely you have any blockage inside the canister and far more likely your control valve/Rochester valve and/or your purge valve has siezed in the closed position.

Cheers,

Don

Don

Thanks for your thoughts re the carbon canister, I will delve into this and its associated valving next year.

As far as I can see there are two check valves. One at the bottom of the fuel module, which effectively allows fuel flow (@ atmospheric pressure) into the module but not back to the tank, the second is in the cap of the fuel module which maintains pressure on the delivery piping thus making starting easier. Q: what was your reason for installing the CV? I suspect that you could have made the task easier by putting the CV inside the tank, i.e. cutting into the flexible delivery tube.

Presently the car is running great, except that she needs two cranks to start when hot. I put this down to having no CV's on fuel delivery. I can't figure out why she starts first time when cold, but I am not complaining about that!

I installed the CV because our '93 was a bit hard to start and installing a new FPR did not improve things as much as I had hoped. I didn't have the fuel tank out or I could have installed the check valve there as you suggest. The easiest place to install it is in the flexible inlet line near the fuel rail, and that's where I first installed it. When I dropped the IRS to rebuild the differential, I moved the check valve to under the fuel tank, not realizing how much more challenging the steel braid reinforced hose would be to work with.

Cheers,

Don