Hello all. I have just bought a 1976 V12 XJ for the father-in-law, it had been stored and not stared in a couple years. Whilst great condition and low km, there is an issue trying to kick it over. Fuel doesn't seem the be an issue, engine will kick and start turning over for perhaps 3 seconds and then shut itself down. I am sure it must be electrical / sensors. Are there any thoughts out there on where to begin testing ? Thank you Jason.

 

Jason,

First and foremost, welcome.

Please drop by the "new members area" when time permits, and do your introduction scribe.

The PreHE is prone to "EFI trigger board" issues. Which is pretty much what you are describing. It starts on the "prime charge" and since the trigger board is not pulsing the injectors, it will not continue to run. Rather normal.

The trigger board is INSIDE the distributor, and the original board is a 3 wire unit (reed switches imbedded). Replaced now with a 4 wre board (Hall effect sensors). The 4th wire is a 12v IGN feed for the hall's, and is a very reliable unit.

The list after that is VERY, VERY long, and I have most of it in the laptop and my very old head.

Very systematic diagnosis is mandatory, or you will be following your rear end for years to came. Been there done that.

 

Hi Jason,
As grant mentioned, shoot over to the new member area and post a welcome thread. A warm welcome and very much help will follow.

New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum

 

Hi. Thanks for the electrical advice. I removed the trigger board and it looks brand new, it tested for continuity on all points also so I have put it back it at this stage.


Over the years the previous owner has done his own repairs on the wiring loom, so am chasing all his changes. I DID find a kill switch and have removed it from the system. To no avail.. though in doing this I have found many splade connections are wearing throughout the electrical system. possibly on dead relay also.


Short of new relays and a complete new wiring harness I need a wiring diagram to reference. Does anyone have something like this out there?


Also discovered that I am now not getting fuel pump power as I was earlier. Thought blown fuse but that doesn't seem to be it, suspecting the relay that sparked a little. The hunt continues. !!

 

Get some brake clean and see if the car will run with external fuel. Spray a quick blast in the intake on both sides through the map sensor hose T . Then crank and see if it runs for a bit. Ive kept the V12 running for awhile on a few frequent blasts. Do NOT spray any igniteable into the throttles bodies. It tends to drip down and catch fire. Dont ask how i know. This will help you identify if you have an ignition or fuel problem.

Get noid lamp or a power LED from an old PC. Hook it up to one of the injector wires. Polarity matters so you may have to flip it. Once right... in a dim place... the lamp should flash when cranking. Thats a visual represntation of the injector opening.

I just repaired a V12 BMW using this technique. It ran on brake clean and the injector lamp flashed. There was no tap to measure fuel pressure. It had a bad fuel pump. Took the fuel pump apart repaired a broken brush wire and the BMW was running right for free.

 

I'm having the same problem, it ran fine when I brought it home after a re-paint and now runs only a few seconds and stops.

Harbor freight has noid light test kits for about $40

If it is the EFI trigger board, can it be repaired, if not, where can I buy a replacement?

 

HF also has FPG with an inline adapter that is necessary on the v12. You need the gauge to see if the pressure is dropping shortly after starting. Accuracy is not important in this case so the HF item is good enough.

Fuel Pressure Tester & Fuel Injection Pump Tester

DISCALIMER: You are working with flamable liquids. Please make sure you have a fire extinguisher rated for oil and gas at hand just in case.