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XJ XJ12 ( X305 ) 1995 - 1997

XJ12 and XJR Fuel Pumps

 
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Old 03-06-2018, 01:09 AM
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Default XJ12 and XJR Fuel Pumps

G'day Gents,

Since I put my V12 back on the road recently it has stumbled under hard acceleration.

The V12 X305s and the supercharged XJRs have two intank fuel pumps with normal running on the primary pump and the secondary pump activates on demand.

I thought it might be a clogged fuel filter so I replaced it to no avail.

I then checked the fuel pump relays, the primary pump relay is in the fuse/relay box in the boot/trunk and the secondary pump relay is on the forward wall of the boot/trunk in front of the battery.

Well I found the cause of the stumbling, the primary pump relay was in the wrong socket and so that pump wasn't running at all and the car was operating on the secondary pump only.

The car will start and run on either pump, I checked this several times by removing and replacing the two relays, one at a time. Interesting to note that in the event of a fuel pump failure the car will still run.

With both pump relays in the correct socket the car runs as it should, under hard acceleration the secondary pump activates and man does that thing move!

Cheers,
Jeff.
 
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SleekJag12 (03-06-2018)
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Old 03-06-2018, 02:45 AM
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Originally Posted by watto700 View Post
G'day Gents,
Well I found the cause of the stumbling, the primary pump relay was in the wrong socket and so that pump wasn't running at all and the car was operating on the secondary pump only.

The car will start and run on either pump, I checked this several times by removing and replacing the two relays, one at a time. Interesting to note that in the event of a fuel pump failure the car will still run.
Wow, I didn't know that! Great that all you had to do was put the relay in the right spot. You did well to check the simple things first. The ECU must default to the secondary if it doesn't see the primary. Thanks for sharing.
 
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watto700 (03-07-2018)
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Old 03-06-2018, 12:29 PM
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Nice catch!. I'm looking at a 1996 XJ12 this week. They are said to be as quick as an XJR6.
Rob
 
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watto700 (03-07-2018)
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Old 03-06-2018, 04:09 PM
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Just as quick and allot smoother.
 
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