1987 XJS V12 injector firing problem

I have recently bought a 1987 Jaguar XJS V12 HE Convertible.

It has been left in a barn for the last 8 years and I am trying to get it started.
Starter, ignition and fuel seems ok, but the injectors does not open. Not on ignition either. It’s a Lucas system.
I have checked the main relay and it gives 12V to the ECU (16).
I have cleaned the resistor and its connector and I can measure 12V from all pins and to ground. (See picture 1 below)

I have pulled one of the injectors from the motor and if I supply 12V directly to it, it opens and fuel comes out. If I measure on the two pins in the connector to the injector, there is 0 V. If I measure from either pin to ground, there is 12V. See picture 2

From the resistor to the injector there is this connector I have cleaned it and measured 12V on it as well.
See picture 3

For me it seems I’m missing ground somewhere or have a short circuit, but I’m a bit stuck now and hope somebody can help me with what I should check next.

For me it seems I’m missing ground somewhere or have a short circuit, but I’m a bit stuck now and hope somebody can help me with what I should check next.

Check the white shielded wire leading from the ignition amplifier to the firewall. It’s the small black box that sits on the B Bank intake manifold. The signal wire inside the shielded wire is probably broken. Thoroughly covered in Kirby’s book. SD Faircloth www.jaguarfuelinjectorservice.com


Per the image, you will see that the ECU grounds the injector groups to open them. Quick and dirty check on ECU is to listen for the fuel pump at key on, should hear it for about 2 seconds. If you do, ECU is powering up.
Next you need to have an ignition pulse from the amplifier on the left intake manifold for the ECU to sense engine rotation; this is via a coax cable from the amplifier to the ECU- notorious for shorting out at the back of the engine.
Hopefully that will get you on the way to figuring it out.

This seems to be little messy. Let’s start from the basics.

You already know that invector is not a pump but sort of valve repeasing pressure.
You already know that most of the cheap multimeters are unable to detect voltage pulse pf yhe injector.
You already know that thicker wires will provide higher amps to the injector.
You already know that injector is a coil with moving core.

Now, knowing what’s above you will know that your ingnition system provide pulse to the injector for a very short moment. You can check it with 12v Led bulb pinned into ignition plug. (You already know that leds are workin one-way only).
If there is a pulse - it may be insufficient to move seized injector, but pulse straight from battery will be much stronger…

Thanks for your suggestions and ideas.

The fuel pump runs when turning on the ignition for a couple of seconds so the ECU should be powered up.

I have measured between the little white wire from the amplifier and to ground and there is no connection.

This evening I tested with a new coax cable, which I welded to pin 18 on the ECU connector. I then attached the other end to the socket from the Ignition amplifier where little white wire normally goes. I removed the original cable in both ends. I didn’t connect the shield when testing.

But the Injectors still doesn’t fire.

I opened the ignition amplifier and it looks good (See picture above)

Can I test the ignition amplifier with an oscilloscope and what should I be looking for.

I would test for an input waveform on the coax lead at the ECU with the engine cranking; should be uniform and a steep rise sine wave. I would think the amplitude would be somewhere around 8v.Then check for the 4 injector ground circuit waveforms at the injectors, again with engine cranking. Again somewhere around 8-12v. Both tests need to be done with everything connected.

If you have spark at the spark plugs (do you?) the amplifier is at least fundamentally operational. The amp’s “trigger” output to the ECU goes thru the resistor block (the white blob). A simple resistance and/or continuity test might be all you need.

Here’s a a little info on the Constant Energy Ignition