Hi all

In my tech support function in Jaguar Club of Denmark I trying to help a member to get his 1984 XJ12 (Series 3) back to life..I know it's not XJ-S, but I think this forum is better regarding V12 knowledge...
I was quite stunned by the first photos he sent. I have visited him, and the outcome (unless I'm wrong) is:

Engine is PreHE. Engine number is 8S17191HAZ, should be from an XJ-S as far as I can see.
Ignition is OPUS. At least it looks like OPUS including ballast resistor
ECU is 16CU (!)

We ordered a DAB113HEF kit to replace the OPUS. That was before discovering the ECU was 16CU. Nothing has been installed yet, so it can be returned.

How would you proceed form here ?
Discard all the OPUS related stuff and get an HE distributor, coil and amplifier (and fix whatever wiring that needs to be fixed) ??
Do anyone have experience cleaning up a mess like this ?

 

Hi, do you have a photo of the engine bay? It may be a rare 10 .1 P digital flat head engine , the injector rail is the clue, in which case the simplest option is install an HE distributor but with the pre he vacuum advance and use the lucas CEI Amplifier and twin 36 cu coils as per all v12 5.3 HE’s until Marelli on the XJS This system replaces the Opus amp, ballast resistor and 16 cu coil, and the amplifier will plug straight in to the existing loom for the ECU speed signal. As standard these engines had the early Lucas 6cu but as the16 cu is mildly programmable then this may have been upgraded at some stage. Dont think the ignition kit you have ordered is compatible with the Lucas 6/16 CU’s . A good 10.1 flat head is a very nice engine!

 

With a 171... engine number, it's a late 1980 engine and therefore almost definitely a P-digital.

Paul

 

Thanks both !
It has the square injector rail as you would expect from a P-digital. I thought it was just another modification. Maybe it’s mainly the ECU that is not original, and with 6CU as the original it’s even a small mod.

simplest option is install an HE distributor but with the pre he vacuum advance and use the lucas CEI Amplifier and twin 36 cu coils as per all v12 5.3 HE’s until Marelli on the XJS This system replaces the Opus amp, ballast resistor and 16 cu coil, and the amplifier will plug straight in to the existing loom for the ECU speed signal.

So I will need a standard HE dizzy DAC4379, a PreHE vacuum capsule, the CEI amplifier box and then cut out the connector to the ballast resistor and get that wired up correctly to the CEI ? It will for sure not plug in directly 😏

 

Hi, you can use the existing vacuum unit and transfer this to the HE distributor. The Opus P digital set up uses an additional feed from the ballast resistor to a shielded wire to send the signal to the ECU, if you trace back the wiring you should find the female connector ( should be just as the shielded wiring starts) and this plugs into the new Amp. Then from the current wiring to the ballast resistor you just need the the white 12 v ignition feed for the new coil and rev counter feed which connects to the amp. Its a very simple set up and in the future anybody familiar with a Series 3 HE will be able to work on the car.
As I side issue you might want to modify/simplify the vacuum advance feed if its running the original set up which uses a mixture of air valves and an oil temperature switch, a simple set up of vacuum at idle and very light throttle works well.
Good luck

 

I'm trying to wrap my head around some of this. An 84 XJ12 with pre-HE engine # (1980 and prior abouts) with a square fuel rail (upgrade obviously) yet retains the Opus ignition, and somehow has a 16CU running it? WTH is that?

Regarding the 16CU, the ONLY way I can see that having happened is if someone spent the money to send an 1986+ 16CU off to Roger Bywater for reprogramming to replace a flakey VERY early p-Digital 6CU for the last year pre-HE.

Moving to the Lucas/GM HEI ignition system with a pre-HE vacuum capsule is a reasonable idea. I presume somehow an inline resistor or some such was fitted to the OPUS system to provide the RPM signal to pin 18 of the EFI ECU to provide injection triggering/RPM signal. (This is usually handled by the 3way split in the negative output (coil control) side of the Lucas AB-14 amp box.

Another possible consideration is fairly cheap, and wouldn't require swapping the distributer. Just get a FAST XR700 ignition V12 kit (like from Moss) to handle the ignition. The only trick would be to re-setup the negative coils side trigger to the ECU through an appropriate sized power resistor (should work but I've never tried this). Even better would be to use the slightly more expensive XR3000 box (very similar price) that lets you use a low ohm coil without a ballast resistor (like a 0.6Ohm single coil that's used to replace the 2 round ones on an HE.).

~Paul K.

You'll have to weigh that against the acquisition of an HE distributer and Lucas ignition.

~Paul K.

 

I checked for shielded cable and vacuum line to ECU. They are present, so we are now aiming for HE distributor (DAC 4379) and an AB14 amp + the single coil DAC 6093.
Before taking this dive we would like confirmation from you guys, that the HE dizzy will be a direct replacement (regarding fit on motor) for the OPUS dizzy.
We have looked into the Crane solution and does not feel comfortable doing this modification.

Regarding vacuum capsule I'm confused if we need to keep the PreHE/OPUS or if we shall update to the HE type ??
I guess it must be HE because we also change the dizzy advancing system by using the HE dizzy ?

BR Leo

 

The distributer should mechanically be a direct fit. But this might be helpful additional reading: There are limits around what I can suggest b/c though I've been able to offer "book" knowledge here, and some practical knowledge, some of what your doing is well outside of what I've personally done, and enters into the realm of "well I've read about that..."

https://forum.etypeuk.com/viewtopic.php?t=15092
(Note their mention of the SNGB ignition upgrade that looks like the Opus box). No exp with that, nor exactly how you'd wire it to the pin 18 trigger of the ECU (though I'd assume the use of an inline-resistor would suffice).

https://www.jag-lovers.org/books/xj-s/05-Lucas.html

And these folks may be able to help you ensure you get the advance/retard correct.
https://www.britishvacuumunit.com/lu...to-unit--.html
https://www.britishvacuumunit.com/services.html
~Paul K.

 

Hi, the distributor will fit no problem, but to remove the distributor you will need an Imperial/Us allen key, metric wont fit. its a 3/16inch. The vacuum advance should be changed to the non he version, the HE gives a lot more advance. Main thing is that once installed you want 24 deg BTDC at 3,000 revs with vacuum disconnected. Good luck Simon

 

Will the SNG Barratt ignition kit DAB113HEF have the correct advance curve for a fuel injected 1976 xj12 pre HE? US and European versions ?