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.
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…
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
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.
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…?