V12 Fuel Supply Issue

Started 21st August 2016 at 13:29 · Laurence Jones

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I have what appears to be a fuel supply issue that I could do with some thoughts on please

The car happily cruises between motorway petrol stations at 80mph for hours on end. However we’re on a trip to France at the moment and have hit a problem when we cruise for hours on end at the French motorway 80mph limit. After about 30 minutes of continuous cruising at this speed the engine cuts if you put your foot down a little further to maybe get up a hill or overtake. This is repeatedly does (sort of a short cut and pick up again).

If I then reduce cruising speed to 70mph for 10 to 15 minutes, I can then comfortably accelerate the car back to 80mph and start cruising again at that speed – only for the same to happen 20 minutes later again.

Oil and water temp is fine throughout this issue

Thanks in advance, Laurence

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- 21st August 2016 at 14:09 #1574
  
  Alex Finlay
  Participant
  
  Hi Laurence
  
  I have had a similar problem twice in my cabbie. The first time it was due to a failing fuel pump. The car would cruise at speed but just pushing the throttle a bit further would immediately introduce a miss. I had about 200 miles to get home and the “cruise” speed slowly got worse. By the time I got home I could only cruise at about 40mph without inducing the engine miss. When I pulled the pump out it was very, very worn. The second time it happened was not long after I had replaced the pump and I couldn’t believe it was happening again. However this time it occurred after I had had the spare wheel out and I discovered that the spare was compressing a fuel line. Once I repositioned the wheel & line it was perfect and has been for the last two years.
  
  So my guess is you have fuel restriction somewhere. I have also had trouble with another car from an old fuel line collapsing internally that gave troubled only when driven at high speed. Couldn’t see anything from the outside though.
  
  Good luck with it.
  
  Regards
  
  Alex
- 21st August 2016 at 19:48 #1575
  
  Laurence Jones
  Keymaster
  
  Thank Alex very helpful response.
  
  I do hope it isn’t a fuel pump failure, as I’ve about 800 mile trip home at the end of this week. I will go now and check the position of the spare wheel – fingers crossed.
  
  Laurence
- 21st August 2016 at 20:03 #1576
  
  Laurence Jones
  Keymaster
  
  Possible result Alex (though won’t know for sure until go motorway cruising again.
  
  Spare wheel was sat on one pipe and held tight that the tyre was squashing the other against the bulkhead.
  
  Have moved the wheel into the boot a bit, so the lower pipe moved freely. I’ve jammed something between the tyre and bulkhead so that when wheel tightened into place it won’t squash the other pipe.
  
  I’ll let you know later in the week when we travel home for the Dordogne if cured.
  
  Laurence
- 22nd August 2016 at 13:27 #1577
  
  Alex Finlay
  Participant
  
  Here’s hoping – you don’t get many cheap fixes with Jaguars!
  
  Cheers
  
  Alex
- 25th August 2016 at 10:50 #1578
  
  Laurence Jones
  Keymaster
  
  Alas Alex it is not to be – moving the fuel pipes has made no difference. Consensus seems now to be is that the filter in the fuel sump may be getting blocked up with crud as we drive for a while, then when we park up it all settled again and all is fine – till the next cycle begins.
  
  Looking at the challenge, I don’t think I can undertake this myself in a carpark 800 miles from home – so looks like we will be having a stop every 1/2 hour or so to let the crud settle and us carry on.
  
  Laurence
- 25th August 2016 at 12:10 #1579
  
  Alex Finlay
  Participant
  
  That’s a shame. Hope it’s not too painful getting home. Good luck with it – let me know when you find the problem.
  
  Cheers
  
  Alex
- 20th September 2016 at 10:03 #1580
  
  Rod Taverner
  Participant
  
  I don’t know how much further you have got with this, but I would support the possibility of crud being picked up by the filter in the swirl pot. On one of my cars, it went from running well to cutting out after 10 mins idling, a time that got progressively shorter until the symptom became start and die. A friend had a suggestion based on experience with his car and a racing XJS. Both ran faultlessly and would then die. He pulled out the swirl pot, found it with a lot of crud and the filter almost completely blocked. Did a clean up and new filter and the problem went away. I pulled the swirl pot out of my donor wreck and found the same issue.
  
  Not for my car, though. Cleaned the swirl pot and replaced the filter to find out, finally, that the ECU was not switching the fuel pump back on after starting. Replaced ECU and car runs without missing a beat. The point here is that the ECU was progressively breaking down from intermittent fault to permanent.
  
  I hope your problem turns out to be the filter.
- 16th December 2016 at 20:40 #1581
  
  Laurence Jones
  Keymaster
  
  Car has been to the garage and upon removing the Fuel Sump (Swirl pot) it was discovered to contain a large amount of rust sediment and the fuel filter was caked up. No wonder that after a 40 minutes the engine was fuel starved.
  
  Garage fitted a 2nd hand Fuel Sump (Swirl pot) and clean filter and all seems well. Additional benefit is that that the persistent smell of petrol inside the car has gone – seems that the whole fuel system is working, including the venting etc.
  
  Happy bunny.
- 31st January 2017 at 19:39 #2317
  
  Terry Vulcano
  Participant
  
  If it happens again – another thing to consider is the fuel cap. The breather hole on mine got plugged causing a vacuum to be created that restricted flow of fuel.
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