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Scary - XJ8 engine cut out on M25


McBreadhead

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Tooling along at 70 in outside lane today when all of a sudden engine just dies. On go the hazards and I fortunately am given space by traffic to coast to a halt on hard shoulder. Plenty fuel, temp normal, gearselector in Drive. Was listening to Duran Duran though.

 

Restarted engine without a problem and set off again. How strange, and how dangerous 😳. I've heard of this on modern Mercs but not on Jags. Any ideas of what to check out?

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I had this on my old tintop and it turned out to be fuel pressure probs (common rail diesel). The ECU just shut the engine down when the pressure dropped too low. Like you I was in the outside lane of a motorway...... not a nice experience *mad*

 


Rik Robarts - the future's bright, the future's orange here

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If it restarted and ran ok the fault was probably the thottle plate getting stuck fully closed. This can be caused by a build up of carbon gum in the throttle body. The thottle plate goes to a reset position (which is past the normal idle position) when you come off the thottle every 5th or 6th time. Engine and road speed have to be above certain limits for this to occour. There is only a partial mechanical link between the thottle plate and pedal so it only comes unstuck when the engine vacuum is lost. All this can be fixed easily with some carb cleaner or brake cleaner. You can push the thottle plate open (gently)and give it a clean up(an old tooth brush works well). Hope this may help.
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Forgot to add that this happened immediately after the AA called out to fix a flooded engine.

 

They had the air box and throttle plate exposed and used carb start copiously; in fact so much the car backfired thru throttle body while I was standing over the car - I nearly jumped a 6ft hedge!

 

I wonder if some gunk got lodged in the mechanism? Anyhow I shall take car in for a check as really do not want a repeat performance.

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How did you flood your engine out of interest? This is supposed to be another common problem with the Jag V8 as it has a habit of over fueling especially if you switch off while it's still in the choke cycle. I though the solution to that one was taking out the plugs and either letting the fuel evaporate or dropping some oil into the barrels. There was apparently an ECU update for this problem.

 

Duncan

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It flooded after I switched it on and reversed for 20 yards then switched off. Apparently they hate this kind of stop/start cycle.

 

It was cured by taking out plugs, blowtorching them dry, then turning over engine with fuel pump fuse removed. Needed a powerful supplement to car battery though (via AA van jump) to eventually get engine to fire.

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So sounds like the traditional XJ problem then. As I say, there was supposed to be an ECU software update to address that particular problem.

 

Fortunately I never had the cutting out at speed or the non-starting problem when I had mine. Unfortunately I did have the crappy water pump and timing chains go which ruined the experience.

 

Hope you get it sorted soon.

 

Duncan

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