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Matt
Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 22001
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My S type 2000 4.0 v8 is intermittently losing all revs at

Resolved Question:

My S type 2000 4.0 v8 is intermittently losing all revs at speeds from 30 down to 3mph and
Comes to a standstill.
On most occasions the battery warning light comes on. The battery is 4 months old.
If I remove the key, wait and re-start the revs will eventually pick up and return to normal.
Thanks.
Rod.
Submitted: 1 month ago.
Category: Jaguar
Expert:  Matt replied 1 month ago.

Hello

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

Customer: replied 1 month ago.
A comprehensive reply from an obviously knowledgeable guy. Not had chance to check out all his suggestions yet but will definitely use Matt again.
Expert:  Matt replied 1 month ago.

no problem

try some of the suggestions and get back to me on this post

Matt and other Jaguar Specialists are ready to help you