Jaguar XJ-S. Manual - part 39

 
 

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the point of being worse than it would be if the proper coils were used.  If you wish to keep 
the killer coil you will need to use the XR3000 amp that is designed to use the higher output 
coil.  Please fix this before proceeding.  You hook it up just as you see in the instructions 
and everything should be fine.  You can also add to the length of the wires on the amp if 
they are of the same gauge and type of wire.  Hope this helps.  Tech support, Steve  
4208..." 

Again, Emin Morali responds:  “When I fit Crane XR700, the car was hesitating to exceed 5000-5200 rpm with misfire 
at the engine.  So I changed the PS20 with PS91 keeping the same OEM ballast resistor pack of my car, but adding a 
serial resistor of 1.4 ohm to protect XR700.  No result, the same problem continued.  This time I throw the 1.4 ohm 
resistor away and used PS91 with OEM resistor pack.  My problem finished.  However the possibility of damaging the 
amplifier pushed me to replace PS91 with a Bosch blue coil (also low primary resistance) by adding a serial resistor and 
no problem at all.” 

Clarkson says the XR700/PS91 setup was recommended by (now defunct) GT Jaguar.  Paul Squire:  “Quoting their 
website:  "Gran Turismo worked very closely with Crane on these systems.  The tech questions they receive about their 
systems for Jaguars are referred to us because they know we have more knowledge in this area than even they do."” 

Terry’s Jaguar (page 693) offers the Crane system, or you can also get it directly from Crane. 

The Crane system comes with a disk with suitable slotted holes for access to the screws in the bottom of the distributor. 

 

LUCAS OPUS IGNITION SYSTEM REPLACEMENT -- ALLISON/CRANE XR3000:  Emin Morali says, “I had 
called a Crane dealer in Florida to ask him if I can use XR3000 with PS91.  After he discussed the subject with a Crane 
tech., he told me that it won't work.  I did not understand the reason why, however I had seen before in Crane web site 
that XR3000 may have compatibility problem with OPUS systems and was not recommended.”  Gee, it seems the 
Crane tech support keeps telling us not to do things that work fine; Bernard Embden installed the XR3000 and it seems 
to have worked out, although he put a lot of effort into locating the amp inside the car and making a bracket he liked for 
the optical pickup inside the distributor.  You can view his installation at 

 

http://bernardembden.com/xjs/ingamp/index.htm

 

 

LUCAS OPUS IGNITION SYSTEM REPLACEMENT -- LUMENITION:  Welsh Enterprises (page 694) offers at 
least two different models of Lumenition electronic ignition system for the XJ-S, each featuring an optical pickup and 
compatible with their engine rev limiters. 

 

LUCAS OPUS IGNITION SYSTEM REPLACEMENT -- LUCAS CEI:  The later Lucas CEI system makes an 
excellent upgrade for the Lucas OPUS.  Buying the Jaguar parts new would be more expensive than just going with one 
of the aftermarket systems above, but if you can find what you need in a junkyard you might get off pretty cheap.  If 
you can’t find the CEI ignition amp for a reasonable price, you can build one with a GM HEI module, a couple of 
resistors, a capacitor, a zener diode, and a suitable box to mount them in.  You can use the Lucas CEI distributor, but 
you must install the vacuum and centrifugal mechanisms from the original distributor in it to maintain the correct 
advance curves for the pre-H.E. engine.  You’ll also need to omit the anti-flash shield used in the CEI distributor to 
mount the D Jetronic EFI trigger board, but they use the same mounting holes so that’s easy.  Make sure to use the 
earlier “green stripe” rotor as it has the magnet in it that drives the EFI trigger board. 

Alternatively, you can reuse your OPUS distributor.  You will probably need to modify it to install the CEI pickup, 
though.  On the CEI cars, the pickup mounts on a metal plate that can rotate with the vacuum advance; on the OPUS 
cars, there’s a fragile micarta part that rotates and holds the pickup.  The body of the OPUS distributor includes a center 
section that this micarta part rotates around, and on the CEI distributor body this center section is gone. 

According to John Testrake, SNG Barratt (page 693) developed a way to upgrade to the Lucas CEI while maintaining 
the appearance of the OPUS under the hood.  “They have marketed it for Ser III E-types which are, of course, 

 
 

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carburetted.  I called them last year and asked if they could do it for an EFI engine.  They said yes and that they were 
just bringing that to market.  I think mine was the first one. 

“They completely rebuilt the dist. from my car with all new parts and refitted it with the CEI reluctor and pickup.  Then 
they swapped the internal parts of my amp with CEI parts and built in a heat resistant mounting.  It's all designed to 
operate with the D-jet EFI and has all the original advance curves, trigger board and what not. 

“And it uses one coil.  It's a Lucas coil with bare aluminum case about 6" long and a white cap where the leads connect 
that says LUCAS.  It mounts to the front of the throttle pedestal like the original.  Pretty standard issue, I think and it 
comes as part of the kit. 

“Everything looks like OPUS.  Nobody can tell it has CEI inside.  I'm hoping for a JCNA North American class 11 
Championship with this car.  So that's why all the fuss over originality.” 

Steve S, who reported above that he had purchased the British Auto/USA-upgraded OPUS amp from SNG Barratt and 
it failed on him:  “SNG being good people exchanged it for one of the CEI units in the OPUS case - although the 
lifetime guarantee is not available with this new one.  I gather the original unit was withdrawn because it was 
unreliable.  With the kit you also get a new aluminium U-shaped resistor pack identical to the original and decent fitting 
instructions.  You have to send your old distributor back in part exchange. The coil, OPUS style alloy box, and resistor 
pack have stickers on them in inconspicuous places warning that this is an updated system with a reference number for 
maintenance in future so standard parts do not get swapped back in.” 

 

LUCAS OPUS IGNITION SYSTEM REPLACEMENT -- $$$:  You could just go hog wild and install a fancy-
schmancy modern high-tech ignition system.  See the ideas for upgrading the Marelli on page 171; any of those systems 
can be used to upgrade the OPUS as well. 

 

Lucas Constant Energy Ignition (1982-89) 

 

LUCAS CEI IGNITION -- DESCRIPTION:  The triggering mechanism for the Lucas CEI ignition system consists of a 
“star wheel”, a wheel with 12 points on it, mounted on the distributor shaft with a “pickup” adjacent to it.  There is a 
magnet and a coil in the pickup.  A magnetic field is established in which the flux passes from one pole of the magnet 
through the coil, through the star wheel, and back to the opposite pole of the magnet.   When a point on the star wheel 
aligns with the core of the coil, this magnetic flux has a nearly continuous path of iron and is therefore at its strongest.  
When the point is far away from the core of the coil, the magnetic flux is at its weakest because there is so much air 
space in its path. 

Since a voltage is generated in a coil with a changing magnetic flux through its core, a voltage is generated in the 
pickup by the increasing strength of the magnetic flux as a point on the star wheel approaches the tip of the core.  A 
voltage is likewise generated by the decreasing strength of the magnetic flux as a point on the star wheel moves away 
from the tip of the core -- but this voltage will be opposite in polarity from the first one.  The pickup will therefore 
produce a voltage that suddenly reverses polarity as a point on the star wheel passes the tip of the core.  The electronics 
within the amplifier module sense this voltage reversal to break the ground connection to the coil, triggering a spark. 

But that’s not all this system does.  It waits a varying amount of time before reestablishing the ground connection to 
begin charging the coil for the next spark, getting the charging started ASAP at high RPM but waiting a bit longer to 
get started under idle conditions so as to minimize coil heating.  It also monitors the current flow to the coil to make 
sure that it does not exceed a set limit, which might happen at low RPM when there is more than adequate time to build 
up a charge in the coil.  If the current rises too much, the amp begins to cut back on the voltage applied, holding the 
current constant and preventing the coil from overheating. 

Prior to systems with such features, coils had to be designed to handle high-current conditions at low RPM and had 
ballast resistors to limit the current.  With the current control features, coils can be designed more compact and without 
the oil inside that was needed to keep them cool.  They could also be designed with very low impedance in the primary 

 
 

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coil without worrying about current overload problems, allowing much faster charging on 12 volts.  Unfortunately, 
such coils weren’t available when the Lucas CEI was introduced, so two conventional coils were wired together to 
accomplish the task.  Later, after suitable coils became commonplace, Jaguar would replace the dual-coil setup with a 
single modern coil whenever a coil needed service. 

During most operation, the ignition amp is merely switching the current on and off and is dissipating very little heat.  
However, at low RPM when it’s having to cut back the voltage to limit the current in the coil, it’s having to dissipate 
that extra power.  It gets hot under such conditions.  The amplifier is bolted to the aluminum intake manifold to try to 
dissipate some of this heat to the manifold and to the cool air passing within. 

Roger Bywater:  “The 12.5:1 compression of the H.E. was too much for OPUS to fire and in any case it was getting 
to be a bit primitive by that time as it had no means of current control other than via the ballast resistor.” 

 

TROUBLESHOOTING: Randy Wilson sends this procedure:  “With the engine cranking, check for: 

 

Power to the ballast source 

 

Power to the coil + post 

 

Ground switching on coil - post  (if so, you should have spark) 

 

Ground to amplifier case 

“If everything passes except the ground switching on the coil, then it’s in the amplifier or its wiring. 

“A scope put on the pickup leads should give a modified sine wave pattern typical of magnetic induction sensor.  At 
crank speed, I think it’s around 1.5V peak-to-peak.  No scope pattern is a bad pickup.” 

“I’ve never personally seen the pickup go bad, but have run into cracked wires in the pickup harness.  Quite often 
jiggling the harness will cause the problem to “correct” itself; sometimes for many years.  Everything working fine after 
doing the scope check is bad pickup wires.” 

If your car runs well when cold but gets uppity when hot and you suspect the ignition amp, you might try pouring some 
water on it to cool it off.  If the car runs well again, you have definitely narrowed the search for a cause down to 
something in that little black box! 

 

IGNITION AMPLIFIER -- REPAIR:  The Lucas Constant Energy ignition amplifier is a black plastic box mounted on 
top of the left intake manifold.  This unit is clearly labeled “Lucas” and “Made in UK”.  The mail-order catalogs call for 
a part number DAB106, and want serious $$$ for it. 

If you unbolt this unit from the intake manifold, turn it over, remove four tiny screws and remove the cover, you will 
see four components inside.  The predominant component is a GM High Energy Ignition (HEI) module.  This unit is so 
common that you can find it on a bubble card hanging from a hook in any department store with an automotive section 
-- for around $20.  Usually this amplifier can be repaired by simply replacing the GM HEI module for considerably less 
than the cost of replacing the whole unit. 

Simple?  Maybe not.  Dave Johnson says, “The amp on my ’84 died on me several years ago.  I replaced the module 
with the equivalent GM module and it lasted 3 months.  I replaced the zener and the capacitor with equivalents.  I again 
replaced the module.  This one lasted 1 month.  I gave them one more chance (lifetime warranty) and it's worked for 4 
years now.  The moral of the story?  I believe the modules available from discounters are marginal and you have to 
keep trying to get a good one.  Since I didn't even consider buying a new amp from the dealer I can't rate their failure 
rate but a GM mechanic friend of mine kept after me that the modules I was getting were junk.  He was right and I now 
have a working one.  No more intermittent problems.  Try another one.” 

Tom Drakos concurs:  “After buying 3 different control modules all made by Wells, DR100, I got 3 different types of 
results, all of which were terrible, to the point of undrivable.  I knew the original was made by GM, so I searched the 
internet looking for a similar application.  I ended up with a control module made by AC Delco, part # D1906, even has 

 
 

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the GM stamp on top like the original.  Price was a little more, $41.00 from Discount Auto, but well worth it.  The car 
runs like new, smooth as silk at all engine speeds and idle. 

“My advice to anyone experiencing a problem with a control module would be not to use WELLS D100...these things 
are crap!!” 

Terry Pegler apparently disagrees about the part number.  “The replacement modules that I am using are AC Delco # 
10482820 from the GM Dealer.  It is made in singapore...”  Doug Dwyer adds that there were earlier part numbers for 
the module, starting with 1875990 in early years, but the 10482820 replaced them. 

Just because you spend the big bucks on the Delco doesn’t guarantee you’ll get a good unit.  Owners have reported bad 
ones of those, too.  Just keep trying. 

Shafi Keisler claims that the standard GM HEI module is rated for 6 amps but the one in the Jaguar V12 is a special 
unit rated at 8 amps.  Nobody has been able to confirm that claim, though.  The standard HEI works great, once you get 
a good one. 

Reportedly some modules come with a packet of heat sink compound.  Tom Bennett says, “I just bought a GM module 
from AC Delco, came with a pack of silicone heat transfer goo.  I am familiar with the usual white heat sink paste; this 
stuff is very different, it's labeled silicone grease and contains 90% polysiloxane 10% silica.”  Hmmm.  Might not be 
heat transfer goo; might just be goo.  Dunno why they’d provide a packet of goo, though. 

Heat sink compound might not be a bad idea; applying it between the module and the ign amp housing might help the 
module run cooler.  Even if the module you get doesn’t come with the stuff, you can get it at electronics shops.  The 
best way to apply heat sink compound is with a single bead, so that when you bring the parts together you squeeze the 
compound so it spreads out.  This way you avoid air pockets in it. 

John Robison says, “Advance Auto has an electronic gizmo they can plug the GM unit into.  It simulates loading at 
both low and high rpm (somehow) and then gives a pass/fail indication for both conditions.”  While it may hardly seem 
worthwhile to check a $20 part rather than simply replacing it, such a test may go a long way toward confirming 
diagnoses.  You might even consider testing the new one you just bought before you leave the store. 

Joe Bialy adds:  “There are 5 connections on the GM HEI module.  The fifth terminal is the ground for the module 
which is actually one of the mounting holes on the module itself.  All of the coil current passes through this connection. 
 If the ground terminal on the module itself is not secure, ignition problems will occur.”  Peter Havas adds, “The HEI's 
on GM engines sit atop the distributor cap, and the replacements must have a second ground wire or they burn up.  I 
don't know why, but having had many GM trucks which suffered spontaneous HEI failure, it was revealed by the local 
GM garage that you must run a straight ground as well as the little flat strip to the HEI to keep it from burning up.  This 
applies only to replacement units, and I have no idea why.  It works though.”  There don’t seem to be similar problems 
in the Jaguar V12 application -- perhaps since the module is securely bolted to the aluminum intake manifold rather 
than to the distributor cap -- but it couldn’t hurt to make sure the ground is solid while you’re in there replacing a 
module. 

Becky Amason says, “Anyone having repeat failures of your ignition modules should check the wires from the stator in 
the distributor for damaged insulation.  This is a known problem with GM HEI ignitions.  The wires flex as the vacuum 
advance moves back and forth, eventually breaking the insulation and shorting out the ignition module.” 

The other components inside the amp housing are a 1 microfarad condenser, a couple of resistors buried in a white 
rubber blob, and a zener diode mounted in the top of the case so the upper surface is actually visible from outside.  The 
condenser may actually be a common source of trouble; there are at least two reports of it shorting out when warm, so 
the engine runs OK when cold but has trouble when warm.  Since the condenser is connected to 12V, it shorting out 
causes it to get even hotter.  Pouring cold water over the amp fixes the problem for a few seconds. 

The condenser is apparently only a noise reducer, being connected to the +12V side of the coil.  As such, just about any 
condenser would probably work.  If you’re looking for a replacement condenser, you might consider the one intended 
for use with the GM HEI ignition system.  Auto parts stores sell a part labelled a “capacitor”, but it’s more than that.  
This part is a little harness that has a 2-terminal connector on one end that plugs onto the HEI module, a 3-terminal 
connector at the other end that plugs into the GM distributor, and a capacitor attached to the 2-terminal connector.  One