Hi: My 04 xj8 with 125K that has run fine for the three years I have had it albeit with some drama here and there scared me suddenly.
I filled tank for 390 mile interstate drive from tucson az to palm springs ca last friday. About 125 miles in, I stopped for a milkshake and when I came out to resume, it cranked, fired, and whimpered dead. Repeated this three times. I removed neg battery cable and touched it to the pos for a moment and reconnected. Car cranked fired and ran perfect for the rest of the trip and back home. I had the idea the computer was confused; that was only reason I pulled cable to reset. Has anyone had this happen? Someone said: "vapor lock" but modern pressurized fuel injection cannot do that can it? Temperature was seasonal 97 degrees. Fuel trims on this car have always been borderline with LT quite rich and ST quite lean. Every once in a while the CE light comes on and I tape up all the air connections under the hood and it goes out. It did come on during drive home for short time but went out on its own. This has happened before. I bought a new fuel cap today wondering if in fact what my friend called vapor lock is a vacuum problem with the evaporation purge system. Thinking a bad cap can affect operation of that system. Thank you for help and sorry for long details.

 

The clue may be the way you have not fixed the underlying fault indicated by the LTFT(s).

 

Have you read the codes?

 

Codes after all this (could not read them in a parking lot in the heat under the gun as it were) were 0171 and 0174 lean on both banks which I have seen off and on over last couple years. I could always get them to be gone after taping up air fittings from PCV, vacuum booster, etc. A few days after this fail, the CEL came on and then went off by itself during highway drive back home to AZ from CA. The codes stored I guess are from that light event which did NOT disable the car. If there were codes from the failure to run, would they be gone after a battery disconnect? Or are these from that event as well?

 

You must obtain the DTCs and fix the vacuum leaks. The o-ring on the brake booster is just one of several areas you may have leaks.

If you're unsure, have a competent shop or Jaguar specialist perform a smoke test to locate any vacuum leaks.

Post the DTCs here along with the LTFT and STFT values. There may be other DTCs other than P0171 and P0174 stored.

 

I am having a hard time accepting that lean mixture which has not immobilized my car yet would suddenly prevent it from running at all. If the trouble were indeed an air leak, why would removing the battery cable and reattaching it restore operation? I did not address any alleged air leak; only rebooted computers.

 

You cleared all the OBD monitors and learned values. It would run rich and try to relearn. Just ignoring things will cause further trouble such as burned out cats.

 

With OBD and torque pro running diagnostics, my car is trimming itself exactly as it has for three years. O2 and mixture are in normal range as the LTFT and STFT are offsetting each other to achieve equilibrium. I realize this is not correct but the net effect seems to be OK.

 

Something's wrong if that happens. The STFTs should move the LTFTs and then the STFTs should end near 0.

 

It is very likely that air leak in the intake system is causing this. I had a bad experience chasing fuel too lean too rich messages and it turned out to be a punctured air intake hose (details here). Did a lot of things as I too did not believe there was a leak in the first place so wasted a lot of energy and money here and there.

 

Did you ever resolve the issue? I'm dealing with the same problem. It started while I still lived in Phoenix but now that I've moved to NJ the cold weather has made it much worse. When temperatures are below 25F outside my 2004 won't run at all. Temps above 25F and it behaves just like yours. I ordered a fuel pump because I'm also getting a P1338 code indicating a problem with the fuel pump drive circuit. Checking voltage from the fuel pump relay up to the fuel pump all looks okay so I'm hoping the fuel pump itself is the root cause. I've smoke tested my intake and I can't find any vacuum leaks. I've also tried removing all vacuum lines and plugging the open ports... no change. This problem is driving me nuts because it makes the car totally unreliable. I refuse to give up on her... there must be a solution.

 

Hi Andrew: About two weeks ago I got a oreilly fuel pump made in hungary off the shelf at a local store for $550. It is in the car but for a time after it continued to throw the p1338 code. I tried running the diagnostic on the cable between the REM and the pump but it makes no sense when the instructions are followed. I gave up and have been driving the car after clearing the codes with torque pro and a cheap dongle. I opened up the REM and put a new capacitor in it. That cost me a whole two dollars. I still periodically get a lean 0171 and 0174 I think it is for a short time but they go away after a while. Local repair place told me my throttle intake boot was porous so I got a new one from reno jaguar. I also have a new PCV pipe from bank 1 to throttle body but something still leaking somewhere. But I have been driving the car around town with no trouble or drama. it cranks starts fires and takes a minute to settle in but runs strong and smooth. I agree this should not be insurmountable. Stay warm in NJ if you can!

 

Last night when it was about 7 degrees outside I got it started after several attempts. I took a can of brake parts cleaner and sprayed various gaskets around the intake before it had a chance to warm up. What I found is that when I sprayed the gap where the upper plastic intake bolts to the lower aluminum intake spacers, the engine stumbled badly suggesting those gaskets are leaking and drawing outside air. In response I've ordered all of the gaskets to completely re-seal the intake, injectors, EGR and throttle. I'll post results.

I went through the REM circuit check procedure as well. Basically they just want you to check each wire for open / short to ground / short to voltage. My patience ran thin given the outside temperature.

Replacing the capacitor is an interesting idea... Sounds like you weren't hindered by a fully potted circuit board. The air suspension solenoid valve block is one giant piece of black epoxy. I'm glad to hear the REM is "serviceable."

 

That suggests quite a big leak and that would in turn make the car unable to get the AFR right and very possibly not start or else die soon.

 

Regarding work on the rear electronic module: mine is not potted with epoxy, everything is exposed. But the giant 1800uF capacitor is the only user serviceable component on that board. I put a 2200 in since that was all I could get at a local parts store. There might be some sealed relays too; density of the board would make it hard to work on at any deeper level. FWIW, my 83 xjs developed fuel pump control circuit failure on its giant single ECM in the trunk. I hard wired the fuel pump relay to stay closed whenever ignition was on but doing that on this would be nearly impossible.