Hi Guys i have recently acquired a 1979 xj 12 series 111 vanden plas .53000 miles
The last owner said it had a fuel pump issue which i sorted (the pump was seized as the car has been dry stored for over 4 years,)stripped the pump and got it working and its pumping fuel up to the fuel filter .The issue is the car will fire up almost immediately will run for a few seconds and then dies.the car will not idle at all.My suspicion is a faulty cold start relay but i really dont know, has any one come across this issue before ? im relatively new to jags i have a xj6 which has run like a top sice i got it over 5 years ago but the 12 is a new machine that i am onlt getting to know my way around any advice would be greatly appreciated i really want to get this big cat purring again

 

The "Could be" list is rather long . And, truth is, you probably have several sub-systems that need some degree of attention.

You gotta begin somewhere, though, so I'd pull the fuel filter and empty the contents into a clean jar. What you see will dictate your next steps. Fuel tank rust is a common issue when cars are stored for long periods and these old Jags seem to be especially vulnerable.

If the contents of the filter is brown muck...and I'm betting it will be....then at the very minimum you'll have to drain the tanks and add fresh fuel. Possibly more...but we'll discuss those options after you report back.

I doubt that the cold start system is to blame as it operates only when the key is turned to the 'start' position....and you report that the engine starts easily. You don't have a starting problem; you have a running problem.

Others will chime in with other ideas.

Cheers
DD

 

Adding to Dougs suggestions.

PreHE V12 Injector pulse is pure and simply controlled by the trigger board inside the distributor, under the cap and rotor.

The fact it fires and runs for a very few seconds sounds horribly like the trigger board is not doing it task, and the engine is running on the Cold Start fuel for that few seconds.

Lots of things to test first and foremost.

Turn ON the Ignition, and then open the throttle, and LISTEN for the injectors "clicking". If so, GOOD, if no, report back, and more steps will follow.

Look at the rear of distributor, and there will be a bundle of wires (flat section) of either 3 wires or 4 wires. Report what you find, as the testing procedure for 3 and 4 is different.

Clean fuel, as said, is paramount, and anything less is a waste of time.

 

Thanks for the reply guys,In relation to your post Doug i rigged up a temporary fuel tank to supply the pump and flushed the lines clean before i reconnected the fuel filter(although i will now check the fuel filter as you suggested) and i also did as grant suggested as in turn on ignition and check for clicking noise from the injectors when i open the throttle(which it does) in addition i checked the distributor and it has three wires going into it (red,black and yellow)

 

OK.

That 3 wire is the original set up and reliability was non-existent.

Test is simpler than the 4 wire, yippee.

Remove the dist cap, take care here please, as lots of OLD wires could be damaged.

You will need a magnet on a stick, or similar. Each end of the now visible trigger board has reed switches imbedded in that mastick stuff. Wave the magnet over each end, and LISTEN carefully, so a quiet time here is paramount. You should hear the switches click as the magnet is waved over each end. If you do, good, as they are deemed working, but I doubt that will happen.

If the trigger board is deemed OK, look carefully at the underside of the rotor heel. If you decide to remove the rotor be VERY CAREFUL (they stick like hell to the shaft so be careful not to break anything, and NEVER pull straight up), and you should see the magnet in the heel. Take a nail, any metal nail will do, and see if that magnet is still a magnet. If it is, good again. It is NOT a strong magnet, just a magnet.

Lets know what you find, and then we can continue with the next steps.

 

Ok guys quick update i removed the distributor cap and tested the trigger board as described by moving a magnet over them and (nothing) cant hear a thing,i also took of the rotor arm and tested the magnet (it works).so we can assume that the trigger board is suspect what options do i have can i get an upgrade kit or do the newer xj12s distributors fit?

 

Well done.

SNG Barratt UK had a 4 wire kit a while back.

Talk to Simon, mention the old fart from OZ, he will either hang up or do a deal, he does have a sense of humour, must have Aussie in him somewhere.

The 4 wire is a direct fit, and comes with a new rotor. The 4th wire is connected to a 12V Ign ON somewhere under the bonnet. DO NOT use the coil +ve please.

I used one of the relays on the bulkhead from memory, but mine was a S2. I will keep thinking what I used whilst you get your trigger board sorted.