Irritable 4.2 NA XK8 fuel problem fix. P0191

[J44EAG]

Portsmouth Hon Sec, David Biscoe staggered over to me this morning with his 4.2 NA XK8 experiencing a serious dose of the vapours. This problem might also conceivably be experienced by similar engined X350 and XF owners.

A peeved David climbed out of his car. It sounded most ill. Clearly mis-firing, gutless and almost impossible to get moving from a start. Engine check light only was illuminated. The problem started after David had the car Terracleaned recently. The garage guy apparently struggled to get a fuel feed at the fuel rail and resorted to tapping into the fuel filter inlet to perform the treatment. Most odd, as I immediately spotted the Schraeder nozzle on the fuel rail once we had removed the engine cover. David suffered the car for a while afterwards before bringing it over to me. My iCarsoft 930i only found just a comms error but no fault code when the car was interogated. I managed to clear the check light and the car returned to normal smooth and powerful condition. However, the fault would return about thirty seconds later.

A half hour phone conversation with PTJS1 ensued. I have an issue with my Torque/Android/ELM327 combo presently so we were unable to get any further with that. Thanks for the help anyway, Paul.

In frustration David and I drove over to Jagcare near Portsmouth. We continued to look for any obvious problems with Simon, John Grieves nephew sumising a leak on the crankcase breather pipe as a common fault. Using his dealer level OBD kit, we finally found P0191 which pointed at the fuel pressure sensor on the fuel rail. I dickered about with a rubber vac elbow and also noticed a small 1/8th bore vac pipe diappearing undedr the inlet manifold. This was the same type of pipe that caused me so many problems on my 4.2R X350 earlier this year. Whilst being unable to change the pipe today, just messing about with that and the rubber elbow, must of had some decent effect. Onced again I cleared down the comms error with the Carsoft, the engine note changed and normal service returned. The car then drove perfectly on the way bacck to Fareham and also gave no problems on Davids trip home to Waterlooville on the A3.

The question remains as to whether it was an issue generated by the Terraclean man connecting at the filter and causing perhaps an air pocket in the fuel system or whether it was my messing about with the rubber pipe that seems to have fixed this car.

Comments appreciated.

Mike K

[mike020150]

Thanks for the comprehensive write-up, Mike. A few years ago, my previous naturally aspirated XK suffered a similar issue after a warranty recall visit to a main dealer. The symptoms weren't so severe as those on David's car (just an illuminated warning lamp) but as far as I could ascertain from the dealer after rectification, a clumsy fitter had disturbed what sounds like one of the same pipes whilst working close by. Mike.

[J44EAG]

A phone call today with David, confirms all is still well. The car has not missed a beat since I did the last fault clearance with the iCarsoft 930i.

Some of these faults can be the very Devil to clear out. Members might recall the games I experienced with my XJR last year....all caused by just one rotted 1/8" rubber pressure pipe that ran from the sc pressure manifold to the by-pass actuator. Even having effected a reasonable temporary repair, (cut an inch off the rotted end of the pipe) the fault would be cleared, but for the next day or so would sometimes fault again. Eventually I did manage to clear it permanently and it never returned until the other end of the pipe fell to bits! Deep seated faults can really glue up an ECU with piles of electronic fault junk. In the past I have also resorted to a battery "hard dump" disconnection for twenty minutes or so. Worth remembering the hard dump method if all else fails and you don`t have a diagnostic tool to hand. It is rather cheaper than a visit to a dealer.

I can but only recommend the iCarsoft 930i unit. The Torque Pro app on an Android or Iphone with an ELM327 bluetooth chip is a cheaper option and that works equally as well. Connectivity though can give occasional issues but by and large it is a pretty good piece of kit. Both are very useful additions to any modern Jaguar owners glove box content and can save a huge amount of stress if you are miles from anywhere and your car kicks up a fault. Better than waiting for assistance or spending a sleepless night in a hotel.

Mike K