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XJ40 2.9 non starter, electrical problem, me thinks!!

XJ40 ( XJ81 ) 1986 - 1994

XJ40 2.9 non starter, electrical problem, me thinks!!

 
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Old 01-11-2019, 12:02 PM
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Question XJ40 2.9 non starter, electrical problem, me thinks!!

I recently purchased an '89 XJ40 2.9L, it had been stood for about 4 years, it was taken in part ex for a new "Renault" (I live in France) it's a RHD hence no one over here was interested in it, initially I wanted the interieur for one of my other XJs. However it's bright red so quite unusual, anyway long story short, brushed off the leaves, connected the booster, squirted some fresh petrol into the intake it fired up instantly, but fuel pump was seized (unleaded petrol with additive 4 years old), so fitted a new pump, drained tank and refilled, ran like a dream drove the 25kms home no issues. Once home engine fired up instantly evertime I tried it, it suffered from the normal dash problem, so sorted that, new seals in mastercylinder, Now it won't start, I've checked the spark at the plugs - OK, no fuel coming through, pump's not running checked the relay - relay OK works fine but I have power on all 4 terminals in the relay plug, which can't possibly be correct even on an XJ40.
Has anyone had this problem before or any ideas what I should rip out first?
 
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Old 01-12-2019, 07:24 AM
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Maybe check the connections at the pump? Perhaps something is jumping across the plug. Have you smelled any "smoke escaping from the wires?" Was the key on when you checked for power? And, because it is something I would do, are you sure your test tool was set properly? Good luck!
 
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Old 01-12-2019, 12:27 PM
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Hi Jerry,
There's nothing jumping across the plug, no smoke and ignition on. The test tool is just a basic voltage tester clipped to ground or chassis.
 
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Old 01-12-2019, 02:40 PM
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Ok, one other thing comes to mind- have you checked the inertia switch? It's in the driver footwell on the left.
 
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Old 01-12-2019, 03:37 PM
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So .. what does power on all four terminals mean? are you measuring in an open circuit, where the relay is disconnect? if so, then this cannot be: one of the coil terminals will get an ECM-controlled switched earth, the other gets a switched live. The other two will have a permanent live on terminal 30 and a switched live on terminal 87.

If you are measuring in a closed circuit, i.e. the relay clicked then you started your measurements, then there is a slight chance that your test tool was reading the relay coil's feedback, hence you're reading four power terminals.

Now; the way I test faulty or suspect relays is to trace pin 87 - i.e. the switched output feeding the fuel pump in your case, then inject 12v into that, with the relay disconnected of course. When testing this way on a fuel pump relay, make sure to start of with a pulse of about 4 - 6 seconds, to prime your fuel rails, then start the car. If it starts, then you have your culprit: a faulty relay.

Let us know how you get along, and good luck.
 
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Old 01-14-2019, 08:08 AM
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I checked the relay seperately and it functions as it should, it's the socket that the relay plugs into has power (when tested to ground) on all 4 terminals, possibly residual power, but to my mind it shouldn't have !!
Over the years I ave owned lots of Jaguars mostly series 2 & 3 XJ6s, a couple of E types, but never had an electrical/electronic nightmare like this XJ40, it seems to be wired up for every conceivable option in the Jaguar catalogue, unfortunately it's a base model, no AC, no electric seats, just a sunroof (which still works fine!)
 
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Old 01-14-2019, 11:28 AM
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The Xj40's electrical systems do seem a little intimidating at first, but you will get used to it if you stick it out.

It was a mystery to me when I first got the car but it does all make sense eventually - good connections are paramount in this car and the download-able manuals such as the electrical guide and the engine management .pdf's are a good way to familiarize yourself with the systems.

The 40 is an early incarnation of today's electronic cars and quite different from the earlier Jags for sure, but still fairly simple and owner-repairable. You just have to persevere it will all make some kind of sense eventually!

Larry
 
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