I am working on an 87 XJS and I would like to know if anyone can tell me what is a good single coil replacement for the 2 coil setup. Is there an msd part I could use... also what wiring changes are necessary for this change over. Also I have heard about some of the horror stories related to fuel lines and I was hoping someone could tell ke which ones are necessary to replace also what to replace them with... and where to get them. Thank you so much in advance.

 

My previous owner changed mine out to a single coil set-up and since I haven't owned one with a dual coil set-up all I can do is take a picture if that would help as to the coil and wireing set-up, LMK. My fuel lines were replaced with high pressure FI hose and wrapped in goodyear (IIRC) fire/leak shields...again a picture is probably worth a thousand words.

 

Any autoparts store should have the hi press hose, all under hood fuel hoses should be changed out IMHO.

Single coil, two wires to amplifier, one from harness, then the typical coil plug wire

Front rail FI hoses and shield covers


other side view of coil and FI hoses

Close up of FI hoses and shield

 

For the single coil Google DAC6093....the original Jag part number. Ducellier is a good brand if you can find it but I think various outfits are selling different brands under that number.

As mentioned you really should replace all the underhood fuel lines. 12 injectors, plus the supply, return, and fuel cooler sections. Good DIY project.

Some of the fuel line sections are crimped hose/pipe assemblies which might still be available new from Jaguar..... but they were silly expensive even 10 years ago. No big deal to cut off the crimps and hoses and simply install new hose onto the old pipes.



Cheers
DD

 

As Doug said, the coil used on the later facelift V12s is a single coil, safest to use one of those or its non-OEM equivalent. If you use a non-OEM one (eg MSD), it is important that the impedance (whatever that is) is less than 1 Ohm, otherwise some other bit of the system will be fried. The reason that there were two coils originally was because there was no single coil available at that time that would run 12 cylinders using the HE Lucas ignition above 3,000 rpm.

As for connecting it, trace the two wires coming from the second coil, which is behind the radiator grille, and remove these from the coil by the capstan/dizzy. Then identify which remaining wires go to the + and - terminals of the capstan coil and reconnect them to the same terminals on the new single coil.

Greg

 

I thought all the Facelift V12's were Marelli which are twin coil (one for each bank of 6). That does look like a Marelli coil in the picture.

This is IMPORTANT. If the primary resistance is incorrect it will affect the dwell time, if the coil charges too quickly it will get HOT and (depending on how hot) either eventually fry or go up in a cloud of smoke. If the coil does not charge fast enough the engine will not rev (hence the dual coils in the early V12's)

The Idea behind the dual parallel coils is - coils in parallel (as long as they are in phase) will decrease the primary resistance and inductance giving a faster charge time.

Just for information - Impedance is the AC resistance of something and will vary with frequency (Charge speed). With the coil the 1Ohm is actually the DC resistance as measured with a multimeter.

 

Warrjon, thanks for this correction. My knowledge of facelifts is practically zero, so I am sure you are right. But I think that the Lucas 5.3 litre twin coil setup can be replaced with ONE newer Ducellier-type coil. I believe Grant Francis has done this, using a Bosch coil, and I have heard of others in the UK being advised that it will work OK. Can anyone confirm this for us?

I did not know that too low an impedence would be a problem as well. I have twin coils as original, but at one point I was thinking of fitting an MSD Master Blaster like this:
MSD Blaster SS Coil - 8207

which has a primary resistance of 0.355 ohms. Would this be too low for the system, as I believe the twin coil setup is just below 1 ohm?

Greg

 

That looks like a pretty hefty coil.

Let me clarify what I said and I will try not to get too technical (slap me if I do).

A coil takes X time to charge (4 time constants to be exact) which is governed by the resistance and inductance of the coil. What happens is current flows and voltage increases when the voltage reaches 12Volts (in the case of an ignition coil) the coil will start to heat up, if the coil can not dissipate this heat (before the ignition fires to discharge it) then it will over heat and burn the primary windings.

So in a nutshell if the coil is low in resistance it will charge quicker (a good thing for a V12 at 6500rpm) but will heat up more than a coil with higher resistance. As long as this heat can be dissipated the coil will live.

Most OEM coils have very little in the way of heat sinking. This MSD looks like it has good heatsinking to dissipate this heat. I would think with this coil a ballast resistor would be required to current limit the charging. If I were you I would discuss it with MSD

 

I have just read the spec sheet and a 0.8Ohm ballast resistor is required if installing without the MSD controller or if installed on a non current limiting system.

If power is left on to the coil a 0.4 ohm coil with 12 volts will draw nearly 30amps but with the 0.8Ohm resistor this current drops to about 12amps.

 

Thanks very much indeed for this really helpful explanation Warrjon. So if at some time I fit a MB, then it is the 0.8 ohm resistor in the positive feed to the coil? Even so, 12 amps sounds quite a current! Is that something like the OEM system's current draw?

Greg

 

JTsmks, with regard to your pics, I understood it was not wise to use hose clamps on the HE fuel rail with multiple barbs. The clamp can compress the hose onto the barb and cut it through.
Not trying to be smart xxx, Just not the vehicle to take chances with as far as fuel is concerned

 

My car runs the later V-12 coil in a single set-up and "clamped" fuel hoses for at least 5 years now..so far no "non-reving", no "fried" coil and no ""cut" fuel lines...maybe I'm just lucky! people that use "hose clamps" vice "FI" clamps and squeeze the crap out of them are the one's taking chances...not clamping your hose on a pressurized FI system, now that my friends is taking chances IMHO. Use even pressure FI clamps and put them on snugly, no leaks, no cuts, no worries.

 

Confirmed.

A single DAC6093 coil (or equivalent) can be used to replace the dual coils on the Lucas V12s. Works fine.

I don't know what the *original* usage of the DAC6093 was. But, in any case, it works.


Cheers
DD

 

As you wish

But, truly, clamps of any kind are not required with the barbed-type nipples.

Cheers
DD

 

12amps is the MAX current the system can draw, usually the dwell will be set so the coil reaches enough current to prevent misfires.

Yes the 0.8ohm is in series on the coil supply

 

I just stuck one of these blaster ss coils on my 86 today with new plugs.
idles smooth, runs great all the way to redline. should I be worried at all about this coil?

 

I have no expertise in this stuff, but I am interested to know: did you put the 0.8 ohm resistor in the 12v feed? And maybe Warrjon can tell us if this is a danger or not.

greg

 

Greg,

I have had a Bosch Universal Electronic coil on my XJ-S for near on 16 years now, and as a single, round style, coil has performed well.

It has an impedence of 0.75OHMS.

On the other HE I tried a Bosch "T" coil, MEC..., SWEET, but being a "gell" coil HATED the heat in the back of the V, and died after 5 years. It had 0.7OHMS when new, and was sitting on 2.9OHMS when I identified it as the culprit.

The Bosch coils are now near impossible to find, so I use a Fuel Miser CC215, works just fine. Now on about 7 HE's down here as a single coil.

BEAR IN MIND please, that ALL my V12's and most of the others in the group, have the Lucas Ignition black box mounted out the front of the radiator, where the auxillary coil once lived, and it runs COLD at all times. Might be my imagination, dunno, but I do have the burn mark on the arm, from one of those suckers I leaned on that was mounted on the manifold a very long time ago (that was my car).

The original coils were abot 1.2OHMS each, and gave "about" 0.7OHMS when connected on the HE.

The PreHE only had one coil, and revved to insane levels. Also only had 9.0:1 comp ratio.

My undertsnading of the HE 2 coil set up, was to give the "grunt" to fire the spark in 12.5:1 compression engines. The plug gaps were also lowered to 0.025" to assist that event. Some markets got lower compression ratios, but the UK and OZ got the high one.

 

I did not put in the 0.8 ohm resistor.
so far i havnt seent any issues