Jaguar XJ-S. Manual - part 38

147

Touch the connector quickly several times to the terminal. Do you get a spark now? Then the
pickup coil in the distributor or its wiring, or (less likely) the amplifier, may be faulty. If there’s no
spark, turn the ignition off and continue:

Get a test lead with alligator clips. Clip one end to bare metal on the engine, pull the tubular
connector off the (-) terminal of the coil and clip the other end to that terminal.

Repeat test 4. If you get a spark now, the amplifier or its wiring is faulty. If you get no spark, the
coil is dead.”

OPUS IGNITION AMPLIFIER RELOCATION: The OPUS ignition amplifier is a finned aluminum block that was
originally mounted down within the galley between the cam covers. It gets cooked, primarily after the engine is shut
off and all that heat from the block rises. Dick Russell says that intermittent failures characterized by the tach reading
zero even when the engine is still turning are a sure sign the amp has failed.

Jaguar makes a kit to relocate this amplifier to the plate across the top of the radiator so it stays cooler. The kit includes
a new amplifier and a new pickup for inside the distributor, and costs over $300.

It is possible Jaguar includes the amplifier and pickup simply because the only time their mechanics get a call to
relocate the unit is after the original unit has fried. On the other hand, perhaps the reason the unit was originally located
in such a sorry place was because the wiring needed to be as short as possible, and the replacement amp and pickup
have updated circuitry necessary for the longer wires. According to Jan Wikström, the plugs and wires used on the
replacement kit are different than the original, indicating you’re supposed to replace the amp and pickup together.
However, he simply spliced wires and used his old pickup, and it worked fine. He notes, however, that the wire color
codes changed; it is necessary to open the amp and verify where the wires go to ensure they are connected correctly.

Clearly, crosstalk between the 600 KHz input signal and the output wire back to the amp would be detrimental to
operation, and such crosstalk could be easily caused by the wires merely being located too close to each other for too
great a distance. Also, the output wire picking up any other signals -- such as interference from the ignition wires --
would be ungood.

Reportedly, some owners have relocated their original amps by simply lengthening the wires, and have been successful.
Others have not been successful. At least one owner reports that the official Jaguar relocation kit caused the wires to
pick up so much interference from the spark plug wires that the car wouldn’t run, and he couldn’t get the system to
work until he shortened the wires back to the length of the original.

Russell recommends that ribbon wire with five or more conductors be used to relocate the amp. By using every other
conductor, the unused conductors in between provide adequate spacing between the active conductors to prevent
crosstalk and interference.

Russell also recommends relocating the amp to the firewall rather than the top of the radiator. In his car, the amp was
affected by water and crud thrown up from cars in front of him. Fortunately, he was able to repair it by resoldering
some connections inside.

Perhaps another solution is to leave the amp in the valley and attempt to keep it cool there. Fashioning a heat shield
from sheet aluminum for underneath it will help. Also, see the suggestion on page 124 about cutting a hole in the A/C
compressor mounting plate.

British Auto/USA (see page 689) claims to have “reinvented” this amp using modern electronics. The amp they offer,
part number JLM368/R, looks exactly like the original and is supposedly durable enough that it may be located within
the V; apparently some concours judges will subtract points if the amp isn’t in its original location.

Of course, if you don’t care about concours points, the best relocation idea is to relocate that OPUS system to a
dumpster and replace it with an aftermarket ignition system. See page 150.

If you have a 1982-89 car with a black plastic amplifier mounted on top of the left intake manifold, you have the Lucas
CEI ignition rather than the Lucas OPUS. There is no need to worry about relocating the amp.

148

IGNITION AMPLIFIER -- REPAIR: Referring to the OPUS finned aluminum ignition amp, Jan Wikström says: “As
for the amplifier itself, there is precious little pottery involved. I opened up the suspect one (four small hex-head
screws underneath) and found that while there’s a silicon blob at the cable entry and a silicon slurp for a seal around the
lid, the inside is empty and there is complete access to PC board and power transistor. No need to $pend up on a new
one if it goes belly up; this unit is eminently repairable.”

Phil Stuart says, “There are four transistors in the early Lucas Opus ignition amplifier, one is a big one in a TO-3 casing
for amplifying and 3 smaller ones for switching. I burnt up the smaller switching transistor. It's fixed and running now;
the transistor we finally put in was a ECG128, NPN type. Cost $2.95 CND. The original one was Germanium NPN;
the replacement is silicon NPN.”

PICKUP WIRING: Wikström warns: “One problem I’ve had on both cars is an intermittent break in one of the three
ignition trigger wires coming out the front of the distributor, right in the moulded grommet. This seems inherent to the
design, as the big, heavy three-pin connector flops around on loose wires and should cause metal fatigue as the wire
bends back and forth. I have replaced the wires (solder joints inside the distributor) and applied spade connectors
instead of the three-pin job.”

COIL LOCATION: If you can’t find it, you’re in trouble. If you have the Haynes manual, the caption on the
photograph labelled 10.2 on page 118 says it’s “at the rear of the throttle pedestal” but it lies, it’s at the front.

BALLAST RESISTOR PACK: The ballast resistor pack is shown as item 164 on the Jaguar wiring schematics. On
earlier schematics, it is illustrated as a simple rectangular box with six wires connected to it, but on later schematics
they show three resistors inside. It would probably have been better if they hadn’t done that, because the simplistic 3-
resistor illustration is incorrect and misleading.

Section 86.35.29/3 of the ©1975 ROM is titled “Ballast resistor check”, and provides a simplistic continuity test. It
provides a more detailed illustration of the ballast resistor pack -- also incorrect. Section 86.35.29/4, “Coil voltage
check”, Step #4 includes values for the resistors in the ballast resistor pack, but they’re numbered “Resistor 1” through
“Resistor 3” and “Connection 4” and “Connection 5” with no clue whatsoever what connections they’re talking about.
In section 86.35.29/10, in the latter half of Step #4, inexplicably buried in the midst of a coil/amplifier check procedure,
the resistance values are repeated and the illustration is provided again -- this time with Connection 4 and 5 labelled, but
you’re still left to guess at the resistor numbers. The Haynes manual doesn’t have any illustrations of the ballast resistor
pack innards, just photos of the outside. Is it any wonder that this book has grown to over 727 pages? Anyhow, the
easiest thing to do is to simply provide a new illustration, so please refer to the figure here instead of any of the
illustrations in the manuals.

149

It should also be noted that some of the diagrams in the
Haynes book have differing color codes on the wires; for
example, Fig. 4.1 shows a UW wire where the XJ-S has a
W/U, and a WU wire where the XJ-S has a W/SU.

Mike Morrin explains the tach connection: The power
from the center left terminal through the 7.6-9.2Ω resistor
to the upper right terminal on the ballast pack diagram
(which connects to the W/U wire) “...is the drive current
for the output switching transistor. So, the tachometer
gets its drive direct from the amplifier, not from the coil
circuit.”

“According to the parts books I have here, there was an
early version, used 1971-72 which apparently did not
have the tachometer connection, and the later version,
which was used 1972-80.” Morrin provides part
numbers:

E-type C35883

until engine 7S7559

E-type C37759

from engine 7S7560

XJ-S C37759 all

“C37759 is apparently Lucas 47229.”

There is some discrepancy about the resistor serving the tach. The XJ-S ROM reports it as 100Ω, but the SIII E-Type
ROM reports it as a straight-through connection, no resistor. This actually probably wouldn’t make any difference to
an electronic tachometer; the resistor merely limits current in the event of a short circuit or something. Could the part
number change with engine 7S7560 reflect the resistor? Morrin: “Either way there is a mistake, it says:

"Connection 5 - Tachometer terminal and straight through internal connection (incorporated in later
units marked 47227)."

That 47227 part is apparently a typo in the E-Type manual; it should say 47229, which is what is actually marked on
the ballast packs.

“On reflection, I think the early unit probably had the straight through connection and the later unit the 100 ohm
resistor. There does not appear to be any change in the vehicle wiring coinciding with the change in ballast.”

Note that 86.35.33 describes how to remove the resistor pack. Evidently rocket science, don’t tackle this job unless you
are a very experienced mechanic. At least Jaguar didn’t put any serious errors in this procedure.

If your ballast resistor pack has failed, it shouldn’t be terribly difficult to put together a collection of generic resistors to
replace it. After some discussion about a ballast resistor pack in which that 7.6-9.2Ω resistor had blown, Gary Johnson
suggested “Radio Shack (Tandy). They sell a 10 or 20 watt 8 ohm non-inductive resistor that sounds perfect for this
application.” For the main resistor serving the coil, there are a wide variety of ballast resistors available at any parts
store since just about all cars used them up until the 80’s; it should be easy to find one that will work.

TACHOMETER PROBLEMS: Both John Holmes and Jan Wikström had tachometers that didn’t work, and both
arrived at the same corrective action: they disconnected the tach signal wire from the ballast pack and connected it to
the - terminal on the coil, where it’s connected on every other car ever made. Holmes: “I just know how this is wired
in other cars and did the simplest circuit possible to see if the tach worked. When it did, why change it again?”

LUCAS OPUS IGNITION SYSTEM UPGRADE: As mentioned above, British Auto/USA (see page 689) offers a
replacement amplifier for the OPUS ignition system that supposedly is more reliable than the original. Supposedly.

100 OHM

7.6- 9.2 OHM

0.72- 0.80 OHM

0.9- 1.0 OHM

Figure 10 - OPUS Ballast Resistor Pack

150

Steve S reports, “I had of those BA updated amps bought from SNG in UK fitted to my V12 E. The original OPUS
amp did 20 years and 90k miles in the V and was still working when I took it out after hearing that it was unreliable. I
thought I was going to "decrease chance of a breakdown". The SNG updated unit lasted about 3 years and 7K miles
before failing in the classic opus failure mode - dies suddenly when hot. Fortunately because this was a USA inspired
device it came with a lifetime guarantee (as against a UK guarantee of guaranteed until it breaks).”

LUCAS OPUS IGNITION SYSTEM REPLACEMENT: If you have any trouble with the original Lucas OPUS
ignition system, it is recommended that you simply replace the entire system with a modern aftermarket ignition system.
There are several available, and most of them can be purchased in entirety for less than replacing any defective part of
the OPUS system. And the owners who have opted for such upgrades have universally reported better performance
from their cars. Note: this recommendation does not carry over to cars with the Lucas CEI ignition; that is an excellent
system and there is rarely any cause to ditch it.

Lucas designed the plastic wheel within the OPUS distributor with three slotted holes that enable the mechanic to insert
an Allen wrench, loosen the three screws at the very bottom, and remove the distributor as a unit. If you install some
sort of aftermarket system, you might want to consider whether or not you will be able to get that Allen wrench past or
through whatever is used to trigger the pickup. Of course, it might not be your highest priority; you could always
simply disassemble the distributor in place far enough to remove the wheel to gain access to the screws.

None of the common aftermarket systems will replace the EFI trigger board. The EFI is a separate system that just
happens to have its trigger board inside the distributor. After you’ve removed all the OPUS junk and installed an
optical wheel and pickup or whatever, you will need to put that trigger board right back in. If your trigger board is toast
and you’ve priced a new one, that is definitely bad news. However, Jaguar’s upgrade trigger board -- which uses Hall
effect transistors instead of the reed switches used in the original -- seems to be reliable, so usually you only need to
buy it once.

LUCAS OPUS IGNITION SYSTEM REPLACEMENT -- ALLISON/CRANE XR700: Allison was acquired by
Crane. By whichever name, their XR700 is a popular replacement for the OPUS. Derek Hibbs reports: “My ign amp
died as a result of convected heat last year. A reliable replacement unit was not available so the workshop installed a
Crane Cams unit. The unit itself is located on the RHS air cleaner and it came with replacement pieces for the
distributor because it uses an optical pickup.”

Andrew Holley says, “I removed the Lucas (Prince of Darkness) system and fitted the Crane XR700-0300 system, took
all of about 2 hrs. The car starts first time every time, and seems to run a bit more crisply. It has improved fuel
consumption slightly, but the major benifit is that it now starts instantly , no matter the conditions.”

Steve Douglass says, “After fighting problems (mostly heat related) with the original OPUS system on my car, I
replaced it with a Crane Fireball system that I got from Terry's for $124.00. The kit came with everything I needed to
do the job along with good instructions. The system has an optical pickup that goes in the distributor and an amplifier
that mounts on the firewall. Pretty much like what it replaces. I was able to install the thing in about 2 hrs and the car
fired right up.”

Paul Clarkson had a hell of a time with pickup mounting brackets inside the distributor and ended up having to fab and
modify stuff, but he’s apparently the only one; everyone else claims the system is a simple bolt-in. Emin Morali
replied: “Try to assemble the optical pick-up unit without using any bracket. You use only two screws and it will fit
perfectly in the place of original pick-up unit.”

There is some confusion about which coil to use with the XR700. Clarkson reported, “I invested in a Crane Cams
XR700 amp and PS91 coil. Here is a reply I received from the tech. dept. at Crane Cams in reply to my query about
lengthening the pick-up leads (so I could locate it in a cool place):

"The XR700 is to be used with our PS20 or PS40 coil with the supplied ballast resistor that
comes with them. The PS91 coil has such a low resistance that two ballast resistors are
needed to keep the XR700 from overheating. This also kills off some of the spark power to

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