1977 XJS
 

Hi all, I'm having problems with starting this beast. It has new plugs, new leads, good spark. It occasionally fires and seems like it's about to fire. Any ideas would be greatly appreciated. I have just replaced the injector harness as the other was toast.

Gathering this is the V12 Pre HE beast??

I suspect you have NO Injector Pulse, and that is a riot to sort on these. Kalgoorlie is just the place to keep your fluids up while you sort it.

Under the distributor cap is the rotor, OK, that rotor has a MAGNET imbedded in its heel. Make sure it is there, and still a magnet. NOT a strong magnet, just a magnet.

Below that is a "trigger board", and that has "switches" imbedded in the Mastick stuff, that the rotor magnet activates. These switches then inform the 3 CU control unit to "fire the Injectors"

HOWEVER

The early cars had a 3 wire trigger board, PITA, and on a major scale.

UPDATE, 4 wire trigger board, different rotor magnet, and a 4th wire that went to 12V Ign supply, NOT the coil.

What is fitted to your car please, 3 wire, or 4 wire, as that will alter the next chapter of "Jaguar War and Peace".

Hi Grant, I have replaced this with a new unit and rotor arm from Jagdaim. I haven't as yet checked for injector pulse. What's the best way to do this?

Many thanks for your reply.

Just to add, I've put a fuel pressure gauge on the fuel line in and it slowly gets up to 110 by turning the key around 5 times. It then slowly drops off so I'm thinking its fuel pump related.

I doubt its fuel related at this time, and checking/setting the pressure on a PreHE is FIDDLY at best, SPECIAL at worst, and I will talk you through that later IF needed.

OK, remove the cap, remove the rotor, look at the heel of the rotor, and see if there is a magnet in there, you will see a "square or round" blob if there is Use a nail etc and confirm if it sticks to the rotor. PreHE comes in various guises, and the carby cars have NO magnet, and the stocks get mixed up, you may well have a PreHE rotor, but it is missing the magnet, been there too many times. Doug rarely makes mistakes, but he is human.

Now you need to tell me if you have a 3 wire, or 4 wire trigger board. Look at it, count the wires out the tail of it, 3 or 4.

Then we will continue.

Hi mate, I have made some progress, someone previous has botched the wiring loom and one of the wires to the trigger board was badly connected where it had been previously joined near the brake booster. I have a hall effect trigger board with 4 wires. The rotor button is correct as it has a magnet in it. I checked it when I first got it.
Thanks for your help, its appreciated. I have a feeling it might be TPS as the engine is starting to fire on occasion ie, it starts to run and then dies.

OOPS on my part, I mis-read your "new" from Doug, apologies.

The throttle switch, maybe, they will run and accelerate with that unplugged, mine did, just not too sharp, and the plug was being unplugged by the rubber boot. Super glue fixed that, just a SMALL drop.

That throttle switch (TPS to some) is a mongrel to set up.

A quicky test:

Ign ON, engine OFF, stand on the throttle SLOWLY, and LISTEN, you should hear 9??? I think clicks of the injectors as that throttle switch passes over the internal segments, that is a GOOD sign. Indicates the TPS is talking to the ECU.

Wiring is the weak point anywhere on the system now.

Spark you have, good.

Just looked for my PDf on that switch adjust and the fuel pressure setting, LOST, so I will write them again, just in case you, or someone else, need them.

Yes, i'm getting multiple clicks so that's all good. I've been following your guide on XJS wont run. Very good thanks. The connector to the trigger board is bodgey up so i'm going to check the wires are correct. It's possible I've got one arse about.

That Hall trigger board is not easy to test.

I did mine years ago, and with the Ign ON, Engine OFF, Dizzy cap OFF, and you will need a "magnet on a stick" type of thing. Wave it over one end of the board, and you ":should" hear the Injectors click as the magnet passes over. Then try teh other end.

Being NEW, I doubt they are dud.

More than likely wiring.

Make sure the 4th wire is on a good 12v IGN source, I used the IN to that ballast monster. Using the coil +ve is only 7ish volts, not enough.

Thanks for that Grant. i have the 4th wire plugged in to the ballast resistor. I have clicking at 1 side of the trigger board and not the other, So it's obviously wiring as you suggest.