Hi i have a 1977 xj-s which has been off the road for 16 years, she runs beutifully for about 20 mins and then will start surging when i open it up. If i nurse it she cruises fine but as soon as i put my foot down it will choke. If i stop and switch her off for 5 minutes it runs and accelerates like a v12 should..... for 10 minutes then it will choke again.

i have owned it for the last year and have replaced alot of ignition / fuel system parts. plugs, ht leads , dizy cap, rotor, fuel pump all hoses, fuel filter, cleaned injectors etc.

Any thoughts?

many thanks.

 

Many thoughts in no particular order.

TPS adjusted incorrectly.
AAV not closing 100%.
Throttle bodies full of goo, and/or adjusted out of spec.
The 2 90deg vac hoses, the BIG ones, on the underside of each throttle body are
leaking.
The 2 FPR's are out of balance, and/or set to the wrong pressure. One of mine prefers 29psi on each rail for a sweet running beast. The other is happier at 31psi, clearly a male car.
The OPUS amp in the middle of the V is getting hot, well documented, and is dropping out, and comes back on line once cooled.
The CTS is flaky, not common on the PreHE, but it is OLD now, so anything is possible.
The ballast block attached to the throttle pedestal is having a moment, mine are long gone.
The fuel supply line under the car, the one on teh RH side is crushed. Also teh return pipe on the LH side may be equally crushed, but that usually gives massive overfuel and black smoke.
The fuel tank is not venting, remove the cap, go for a drive, cheapest diagnostic you will ever have.
The small sump fuel tank, the one under the battery, has a clogged filter sock, well documented also.
Ignition coil is getting HOT, and I mean HOTTER than the surroundings, it dies, and then wakes up when cooled down.

Basically, you need to establish if the hissy is fuel or spark related.

 

Cheers Grant,
When you say your balast block is long gone, have you replaced it with an after market part or can you bypass it?
Ill start checking this afternoon.

 

Maaaate, memory, the fun begins.

Both mine are Crane XR700 powered. Bosch GT40R coil, standard Echlin ICR13 ballast, and the tacho's were rejigged by an instrument repair mob to work with coil -ve pulse, instead of the ballast pulse as made by Jaguar.

I then fitted a relay in the start circuit to "boot" the coil with 12v when cranking, that started them all within the first rotation of the engine.

I suppose there are work arounds for that ballast, but I just tossed all the Opus stuff, and went the Crane way. All my cars are Daily Druivers, and reliablity is far more important than anything else.

The XJ12 S2 now has 545000kms, and still rockets along at redline all day when needed. Thats the one set at 29psi.

 

Sorry for the slow reply My first son was born last week so work on the jag was put on hold. But I Drained my tank and pulled the pick up filter out of the surge tank and yes it was very clogged. The surge tank has alot of surface rust and the main tank has a layer of rust on the bottom the rest of the tank seems ok.... So i have pulled the tanks out and dropped them at a radiator repair shop to have them cleaned and resurfaced. Ill let how it all goes.

 

Congratulations DAD.

Good find on the tank gunk.

Be prepared to replace the SMALL "bucket filters" in the inlet spigot of each fuel injector. They may be clogged with that gunk from the fuel line metal sections.

Most PreHE had the fuel filter right on the front of the RH Inlet manifold, and that is a BONUS, as the fuel is final filtered just prior to entering the injection rail.