Experience in a Book
Ignition System

SPARK PLUG REPLACEMENT: Ain't nuthin' easy about this job. Note that it is much easier on the pre-H.E. because the spark plugs are vertical. On the H.E., the plugs are tilted toward the center just enough to make the job truly miserable.

First problem is getting the plug wires off -- and back on later. Jan Wikström: "I've made up a pair of "pusher" tongs out of a bent piece of 4 mm high-tensile fence wire. Same idea as the common barbecue tool, but the jaws originated as a short piece of 9mm copper pipe split lengthwise and brazed to the wire. This gets a good grip on the cable just above the rubber cap on the terminal. This tool needs to be bent to a slight angle above the jaws."

If you have access to a wet/dry vacuum cleaner, use the hose with no attachments to clean around the plugs before removing them. Just poke the hose over the end of the plug. Compressed air can also be used. John Bertsche adds: "I came up with a cool tool for cleaning out the crud around (and in) the spark plug holes. A turkey baster -- pull off the bulb, duct-tape the other part to your shop-vac hose, and you've got a high-intensity, pinpoint (well, almost) vacuum nozzle that'll fit right into the spark plug hole. Works great! You can use it to scrape dirt and crud out of almost any nook and cranny, and it won't scratch the aluminum."

Using normal tools, it generally requires removing the cruise control actuator and unbolting the A/C compressor on the H.E. to replace the 1A and 1B plugs. However, according to Chad Bolles, the plug wrench that comes in the XJ-S tool kit can be used to replace these plugs without removing the compressor. If you don't have this tool (CAC5368) it can be purchased from Jaguar for about $71!

There are T-wrenches sold for 5/8" spark plugs, and a good one might actually do the job. Unfortunately, all this author has found are cheap ones, and the swivel invariably breaks as soon as torque is applied with the swivel in any position other than straight, which makes them worthless for this task.

It is possible to make a suitable spark plug wrench from one of those el cheapo tubular sheet metal wrenches that you stick a steel rod through for a handle. First, you must find a suitable wrench to fit the 5/8" spark plug hex. Cut the other end of the tube off (they always have another size hex on the other end) so that it is flush with the top of a plug when in position. Drill two holes into the tube near the top edge. Then discard the steel rod that came with it (you can't insert it through the holes without going through the spark plug), and instead fabricate a U-shaped handle from some sturdy steel rod. Bend the tips of the U 90† so they point towards each other. Fit these tips into the pair of holes, and install push clips (or drill for cotter pins) on the inside to hold the handle in place. This handle should be free to swing up and down at different angles. You may also wish to cut the corners off either side of the top of the tube to provide a little more clearance to get it in and out. And, even though this wrench will help you tighten and loosen the spark plugs, you won't want to use it to take the plug all the way out; it may get trapped and you'll have to screw the plug back in to get it loose. Once the plug is loose, try the 3/8" hose mentioned below.

As long as you're going to the effort of taking the plugs out, it wouldn't be a bad idea to go ahead and perform a compression check. It's a good way to keep a watchful eye on engine condition.

Before installing the new plugs, it is recommended the time be taken to carefully inspect the threads. Competition is fierce among the plug manufacturers and they generally cannot afford to spend a lot of time and effort making perfect threads every time. One small burr on a steel spark plug can wreak havoc on the threads in the aluminum head.

Be sure to use anti-seize compound on the threads. Do not use normal grease, as this may hamper proper grounding of the plug, and it also may get hot and form a crust that makes it even harder to remove the plugs. And do not use a graphite-based lubricant, as graphite may react with the aluminum and weaken it.

When installing spark plugs, it is helpful to use a piece of 3/8" hose to get them started. Press the hose firmly over the top of the plug and use the hose to feed them into place and thread them in finger tight. Then the hose can be pulled off and a socket used for final tightening.

There are warnings not to tighten the plugs past 8 ft-lb. of torque. 8 ft-lb. is not enough to turn the plugs loosely in the threads unless they have been recently cleaned and chased, but the point is well taken. It is an aluminum head, and tightening "three grunts" is both unnecessary and costly. Just tighten until you feel them seat, make sure they're snug, and quit.

SPARK PLUGS: A quick survey of a group of Jaguar experts clearly indicates that NGK is the plug to use. The study may have been unscientific and the reasons may have varied, but the consensus was clear and overwhelming.

Lots of Jaguar owners seem to feel that their car is worth Bosch Platinums, but the fact they are tricky and expensive may not be helpful. Randy Wilson says "I've found that Bosch standard plugs do not perform quite as well as Champions or NGK, but are better than most common American plugs. I have, however, never had any success with their platinum plugs. If the engine is running well, they don't seem to make any improvement, and if the engine is not well, they foul easily and are not cleanable."

The H.E. engine uses taper seal plugs; the pre-H.E. engine uses washer-seal plugs. For the H.E., NGK makes at least two plugs, TR5 and BPR6EFS. Both are resistor type, but the TR5 is a "V-Power" plug with a little notch cut in the center electrode.

There are many gimmicks used to sell spark plugs these days. There is one common feature that may be of some benefit: it is easier for a spark to jump to an edge or point than to a flat surface. This is why lightning rods are pointed. Many of the cute configurations of spark plugs result in there being more edges on the electrodes, instead of flat surfaces. The notch in the center electrode of the NGK V-Power plug is such a feature.

There is no appreciable disadvantage to using resistor plugs. The resistance limits the current flow, which in turn reduces spark plug wear and radio interference. Prior to the actual spark, there is no current flow so the resistance has no effect on the voltage available at the electrodes.

Note that the pre-Marelli ignition H.E. engine generally calls for a 0.025" gap (check decal on underside of hood). Plugs come out of the box with a 0.032"-0.035" gap. The gaps need to be adjusted prior to installation.

Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:

A new design sparkplug, BR7EF, incorporating a V groove earth electrode, is fitted to improve efficiency and provide better firing consistency.

SPARK PLUG GAPS: The proper gap for the pre-Marelli H.E. engine is 0.025" -- you can confirm this by checking the decal on the underside of the hood. Reports are that some dealers are installing spark plugs with 0.035" gap, regardless of which year XJ-S they're working on. If your dealer is doing this, the least you should do is never darken their doors again. Better yet, file a complaint with the EPA, since spark plug gaps are an "emission critical" specification (that's why it's on the decal under the hood) and it is illegal for them to be violating it.

STRIPPED SPARK PLUG HOLES: Since you have read this book, used anti-seize compound on the spark plug threads, and didn't overtighten, you will never strip spark plug threads. However, the PO or the idiot you've been taking the car to for service may not be so careful and leave you with plugs that simply won't come out without bringing the threads with them. Aaargh!

The official Jaguar fix involves recessing, drilling and tapping the holes for larger threads, installing an insert, and installing a small pin to prevent the insert from unscrewing. Note that the inserts will be different for H.E. and pre-H.E. engines, since the pre-H.E. used washer seal plugs while the H.E. uses taper seal plugs. Generic inserts may work fine, but regardless of insert used the head surface should be recessed prior to installation to ensure that the tip of the plug will be positioned at the same level as before. If the surface is not recessed, the plug will seat in a slightly retracted position and result in a lower compression ratio on that cylinder as well as possible effects on the swirl pattern in the H.E.

SPARK PLUG INDEXING: Does "anal-retentive" have a hyphen? If you answered yes, you may be interested in knowing that "indexing" spark plugs may improve performance in the H.E. engine. In the H.E. combustion chamber, the compression stroke squeezes the fuel/air mixture out of the area over the inlet valve and into the area over the exhaust valve, causing a swirl. This fuel/air mixture is swirling when the spark occurs. If the ground electrode on the spark plug happens to be positioned with its back side into the swirl, then the spark is partially hidden from the fuel/air flow, possibly hindering proper ignition.

To avoid this, mark the side of each spark plug with an indelible magic marker to indicate where the ground electrode is. The position you want to avoid is with the back side of the ground electrode aimed toward the nearest end of the head; in other words, you don't want the electrode on the spark plugs in the front three cylinders on the forward side and you don't want the electrodes on the spark plugs on the back three cylinders on the aft side. If any end up in these positions when installed, then exchange that plug with another.

Please do not use a lead pencil to mark the plugs. Graphite conducts electricity, and will cause "tracking" down the side of the ceramic and short out the spark plug. Your engine will run much worse than before you indexed the plugs.

SPARK PLUG WIRES: If your ignition wires need replacing, there's really no reason to buy the Lucas originals; you should be able to purchase two 6-cyl or 8-cyl sets of high-quality ignition wire sets from any auto parts store and combine them into a set for the V12. Here are some tips:

You can get anything from a roll of wire and a package of connectors all the way to completed, ready-to-install sets; I used a "semi-tailored" set -- one end of each wire comes with the spark plug connector attached, but you cut the other end to length and attach the distributor cap connector yourself. The wires on the V12 are shorter than most, and this permits the right length so you don't have lots of excess wire laying around.

Another feature to look for is the angle of the spark plug connector. Some are straight, some are 90 degree, a few are 45 degree. What the V12 needs is a slight bend; the ideal kit has connectors that are straight to begin with but can be bent to whatever angle is needed. This allows providing different bends at different cylinders -- working on these plugs, you need all the help you can get!

Of course, silicone wires are a must.

There is also the choice between 7mm and 8mm wires. Ideally, one would choose 8mm wires, since the Jaguar ignition system is really hot. However, I couldn't find an 8mm set that had the type connectors to fit this distributor cap; the 8mm sets all fit caps that the connectors look like the top half of a spark plug rather than holes. So I ended up with a 7mm set.

Most aftermarket kits seem to be bright colors. Deal with it.

Jim Belkoff writes, "I found that Pep Boys can special order a custom set of 8mm silicone wires that are made in the US by Borg-Warner. I paid the $45 in advance and picked them up a day later. They are of high quality and include three wires with 90-degree plug boots (for the number one wires at the compressor and another location - your choice, I guess). The kit even came with a tube of dielectric grease.

"For those of you who don't like the bright aftermarket colors, take heart - this set has tasteful light grey wires, black plug boots and dark grey distributor boots.

"The length was very close on most, and exactly spot on with some of them. Even the ones that were a shade long weren't so huge that they flopped every which way. I have had problems with aftermarket wires in the past (mostly semi-custom 7mm sets) and these are the closest in length and the highest quality I have used so far."

John Smith of Brisbane, Australia says, "I noticed that most parts shops have made up spark plug wires in a variety of lengths. I bought a set, nice blue colour, that had 90 degree connectors for the distributor and straight connectors for the plug ends - the same as the original wires.

"I measured the various original wire lengths and these are:

1A	38cms (15 inches)	1B	43cms (17 inches)
2A	25 (10)	2B	35 (14)
3A	28 (11)	3B	17 (7)
4A	30 (12)	4B	25 (10)
5A	40 (16)	5B	38 (15)
6A	38 (15)	6B	46 (18)
Coil	19 (8)

These wires were 8mm and fitted perfectly."

Greg Benjock bought an 8mm Belden Wire set from NAPA and was not very happy with it. "The custom ordered kit came with wrong terminations (all were 180deg). All 13 terminations on the distributor cap in fact must be 90 deg type. And terminations and boots for plugs 1A, 6A, 1B, and 6B are best fitted with 90 degree units. It looked very much like an inexperienced person put the job together." Of course, maybe the cap connectors are a matter of opinion; this author's are all straight connectors and work just fine!

All that said, it should be noted that the original Lucas wires are usually not very expensive; the only valid reasons for using aftermarket wires are availability, a need for a dash of color, and a healthy contempt for all things Lucas.

CAP AND ROTOR RENOVATION: Most of us just buy new parts periodically, but Danny Rearden says, "High tension ignition components such as distributor caps and rotors are generally only faulty if they are cracked, or have carbon tracks on the surface. Even both of these conditions are usually repairable if you are prepared to invest a few hours. My dad specialized in repairing obsolete vintage and racing ignition systems and magnetos where parts were completely unobtainable.

"Clean the part, first with solvent cleaner, then with strong hot detergent solution and dry thoroughly. Inspect very carefully, with a magnifying glass if your vision is not 20/20, looking for any surface marks which were not intended to be there.

"If there is no visible sign of high voltage tracking, go to polishing. Otherwise use a hobby knife and scrape the surface until you get to totally clean material, even if this means making a hole in the component.

"Grooves and holes can filled with epoxy filler. We always used Epiglass Low Density Filler, designed for boat repairs. It seems to have very good thermal and electrical properties, and it does not run while curing. File and sand the repair back to original profile.

"Polish out any marks (both in the original part and any repair), using abrasive paste, such as perspex polish or cutting compound. These surface marks, if not removed, will be future failure points.

"If the part has a dull, porous look to the surface, a light spray of a suitable clear paint may be in order, but don't overdo it. If the repairs were to a visible part, then coloured paint can be used.

"In the 25 years my dad was doing these repairs, I can only recall 1 or 2 items failing again, out of several hundred, and these were subject to 'owner abuse'.

"The important things are:

• remove any trace of previous tracking
• polish or fill any holes, cracks or scratches which could accumulate dust and moisture
• stop moisture getting into the ignition in the future"

IGNITION SYSTEM TYPES: There have been three distinct types of ignition system fitted to the XJ-S. Up to 1982, the car was fitted with the same Lucas Opus system that was used in the Series III E-Type. This system uses a plastic disk with 12 ferrite inserts within the distributor to trigger the ignition. From 1982 to mid-1989, the Lucas Constant Energy ignition system was used; this system uses a 12-pointed iron star wheel inside the distributor. These two systems can be distiguished by the amplifier; the Opus amp is a finned aluminum block that may be located between the banks, on top of the radiator top support, or any of several other places; the Constant Energy amp is a black, flat rectangular item bolted to the top of the left side intake manifold.

It must be clarified that the most obvious distinction within the Lucas distributors has nothing to do with ignition types. Up until 1980, the XJ-S had a Bosch D-Jetronic EFI system that required a trigger board within the distributor and a rotor with a magnet in the counterweight. From 1980 on, the Digital P EFI system was used, and it merely picked up a signal from a coil wire -- no trigger board required. So, the same four screw holes in the distributor housing were used to mount a clear plastic anti-flash shield, and a new rotor with no magnet was used. A different cap was introduced to go with the new rotor. The Opus ignition system, with the plastic wheel, continued in use for two more years.

In mid-1989, the Lucas Constant Energy ignition system was replaced with the Marelli, which is an all-electronic system -- there are no mechanical or vacuum advance mechanisms, the timing is handled by an electronic control unit based on crank sensors. The Marelli system still uses a distributor, but it only serves to allow two coils to fire twelve cylinders; it does not include any timing or triggering functions. This distributor is very distinctive, in that the cap has connections for two separate ignition coils, one at the center and one off-center, and has no vacuum advance module.

On to the Lucas Ignition