Need help with XJ12 1984 fuel injection, DAC3062 pin 18


I am a car mechanic, and I am working on an XJ12, 5.3 1984 which does not inject at the moment.
It has a DAC3062 controller. The problem is that pin 18 Engine speed is not connected and hanging loose. I am not sure where to connect it to. So far I understood it should be connected to the amplifier.
The amplifier is mounted in front of the engine bay above the water cooler and not on the engine like I saw elsewhere and has 6 wires.
3 to the hall sensor, 2 to the 9BR Y47229A Ignition Ballast Resistor Block and one to the ignition coil.

So my question is where to connect pin 18 to.

Thank you very much.

I might add we got the car in a not running condition with the task to repair the ignition, which we did.
So there might be a mismatch between the ignition and injection system.

What color wire, Claus…?

In principle, the ECU uses ignition pulses to ‘read’ engine rpms, of course - triggering injection, all injectors, one every engine revolution. As the amplifier alternately ‘makes’
and ‘breaks’ coil ‘-’ ground, the usual set-up is to connect the ECU #18 to coil ‘-’ instead of a separate connection to the amplifier itself. However, different ign amps were used, and my manuals are not clear - a resistance may be required and the #18 might then be connected to the resistor pack…

Obviously there is no ready place for the disconnected wire to connect to the amp or resistor pack…?

Others may know better than me - but welcome on board…

xj6 85 Sov Europe (UK/NZ0

It might help to properly identify the car and ignition system. It sounds like you have a “Pre-HE” car with the older Lucas Opus ignition (as opposed to Lucas CEI) which would make the car older than 1984; probably more like 1980-ish.

Along those line it would then have the older fuel injection system, perhaps D-Jetronic?

I’m still on my first cup of coffee. But this might help?


Doug, Your info is pretty dang close. There’s an archive post from waaay back on July 2000 on the XJS forum titled “ECU”. Within that post, Mike Morrin collected a list of ECU’s and the year vehicle, etc. His info indicates DAC3062 is a 6CU used in 1981 in the HE engine with Lucas CEI and no O2 sensors. SD Faircloth

1 Like

Which would be in conflict with (what seems to be) the OPUS ignition the OP seems to have.

With the last 6 digits of the VIN and/or build date we can probably begin narrowing-down what you have and then, hopefully, refer to the correct service manual info and wiring diagrams


the white wire should go to terminal - of the ignition coil. But neither with 6-8 ohms resistance nor directly do we get the signals to the injectors.
If there is loose contact from plus, the injection nozzles open once time.

Hello, it looks like a HE engine with a pre HE ignition system.
The chassis number.


Thank you for the effort

The 1981 model year began with 320xxx, at least for USA market cars.

The HE engine was introduced sometime during 1981 calendar year.

According to Jaguar the DAC3062 was used beginning with 326520 but not for all markets.

Anyhow, I would look for pre-HE wiring diagrams and go with that.

I have some of that info but it’ll be a few days before I can put my hands on it. Others here might have info closer-at-hand


Does that mean that the ‘loose’ wire is white, Claus?

Which would be odd; in Jaguar color logic white is a circuit powered with ign ‘on’. Ie, white wires are supposed to deliver power to ‘something’. The ‘normal’ color for amp/coil to ECU is white/black - where the /black generally denoting something connecting to ground…

This is a general ECU feature; as ignition is turned ‘on’, powering up the ECU, the injectors click once…

As Doug says; getting the appropriate wiring diagram, or ‘all’ diagrams relating to the V12, seems relevant - though not that it seems easy…

As an aside; in ‘most’ cases, being rather long the relevant connection from the ECU amp or wherever, is split by a connector ‘midway’. Any chance that the loose wire is disconnected from a similar connector somewhere in the wiring loom? The type of connector on the loose wire may be a clue…?

xj6 85 Sov Europe (UK/NZ)