Jaguar XJ-S. Manual - part 71

 
 

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unconcerned about appearance, it is a simple matter to relocate the harness right up on the fuel rail and tie it in place 
with zip ties. 

If your harness is already cooked, consider fix #2 -- rebuilding the harness using better wire.  Sawyers:  “The real 
McCoy seems to be Raychem Flexlite High Performance wire.  This stuff is double insulated, with a primary insulation 
of radiation crosslinked polyalkene, and a jacket of modified PVF2.  Operates at up to 125°C and has excellent 
chemical resistance (ie oils for us) (they say).  The problem?  It is a factor of ten more expensive than standard 
automotive cable.  This means (in US speak) about $1 a yard for the most common gauge.” 

Another possibility is Teflon-insulated wire.  If you find a source, buy it and use it.  Of course, asbestos-insulated wire 
would work great, but isn’t recommended anyway. 

Del City (page 704) offers “cross-linked polyethylene” insulated wire which is supposedly good to 177°C (350°F).  
That oughta be enough! 

Del City will add stripes to wires if you want, but it’ll probably entail minimum order sizes beyond reason for the home 
mechanic.  If you find sources of small lots of color-coded wire, good for you, but if you’re limited in colors you can 
color code them with pieces of heat shrink tubing, or even type up little labels and fasten them to the wires with clear 
heat-shrink tubing.  If you wanna get fancy, there are professional wire labelling products available. 

To end up with a reliable injector harness, you can either rebuild the one you’ve got or make an entirely new one from 
scratch.  Either way is about the same amount of effort, but rebuilding the existing one requires less thought.  Just mark 
which plug goes to which cylinder, then take the whole thing off and lay it out on the bench.  Strip all the wrapping.  
One by one, cut out the dried, cracking sections of wire and replace them with new sections.  Use heat-shrink tubing to 
seal all soldering jobs.  Of course, you may choose to replace injector connectors while you’re at it -- see above. 

Making a new one from scratch is not only not really any more difficult, but it results in a considerably neater 
appearance and more pride in the accomplishment.  Again, take the harness off and lay it out on the bench and strip the 
wrapping.  But in this case, merely inspect it to see how the wires are routed and connected, measure the lengths, and 
make an entirely new harness.  If you wanna get professional about it, you can lay down a sheet of plywood and 
hammer nails into it as a guide to making the new harness, but this really isn’t called for on a one-time job. 

There are even a couple of minor changes you might make to your new harness.  When this author did this job, one 
change made was the location of the section of the harness that passes from the right bank over to the left bank side.  
On the OEM harness, this bundle of wires passed under the A/C compressor.  The new harness was altered slightly to 
have this bundle pass to the rear of the compressor and under the cruise control bellows instead, a much more 
convenient location. 

You probably won’t be able to find a replacement for the big plug at the right side fenderwell, but the original one is 
probably OK due to its location away from the serious heat; you can merely dyke it off and splice it into the new 
harness assembly.  If you would rather replace it, you can get some generic connectors and replace the connector on the 
end of the harness on the right fenderwell that the injector harness connects to.  You need connectors with at least five 
terminals (the original has eight, but you can combine some).  You can, of course, connect them up with multiple 
smaller connectors, or even a bunch of individual spade connectors, but that would look crummy.  Perhaps the best 
connectors available are called Delphi-Packard automotive connectors; they are commonly used in modern GM cars, 
and they are completely sealed so they won't corrode.  They are likewise available from Del City; you can use either a 
single 6-pin or two 4-pin connectors for this job.  If you choose to use two 4-pins, you might actually opt to create two 
completely separate injector harnesses, one per bank. 

Del City also sells new high-temperature looming, but if you want you can just bundle the wires with zip ties every few 
inches and leave them visible. 

If you’d like to review some photos of the injector harness work, visit 

 

 

http://www.jag-lovers.org/xj-s/book/InjHarnessRebuilding.html

 

I know what you’re thinking: “Too much effort; I’d rather just buy a new harness.”  Wrong.  First off, you clearly have 
no comprehension of just how far Jaguar can gouge the customer for a few wires and connectors; once you price this 
item, after they pick you up off the floor you will be shopping for wire and a soldering gun.  Second, remember that a 

 
 

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new Jaguar harness is made from the same cheap PVC-insulated wire the original harness was, so all that money only 
buys you a temporary fix -- it will soon be cooked again.  Better to do it yourself and do it right. 

Also note that the injector harness accounts for most of the wires in the V, but not all.  Once you’ve got the injector 
harness fixed, you’ll probably want to similarly upgrade the other wires in the area. 

 

RELAYS:  There are several relays involved in the EFI system.  They are discussed along with all the other relays in 
the car starting on page 560. 

 

FUEL INJECTORS:  If your engine is running or idling rough, one possible problem is a plugged or bad fuel injector.  
This may be indicated if the misfire always seems to be the same cylinder, although a bad spark plug or wire or 
mechanical problems in that cylinder are other possible causes.  One-cylinder problems have different symptoms than 
they would have on a carburetor system, because a misfire in one cylinder causes the fuel and oxygen to enter the 
exhaust unburned.  The oxygen sensor will pick up the excess oxygen, and the ECU will conclude that the engine is 
running lean.  The ECU will then richen the mixture to all 6 cylinders on that bank, and then the whole bank sounds 
bad, not just one cylinder.  If you have catalytic convertors, they might start getting toasty as well -- see page 316. 

If you have a trip computer in the car, chances are pretty good that the indicated fuel mileage doesn’t agree with the 
actual mileage determined by the odometer and the fill-ups.  However, the error should be pretty consistent -- off by 
about the same amount every time you check.  There have been some reports that a sudden change for the worse -- the 
actual fuel economy gets quite a bit worse while the trip computer is still indicating about the same as before -- may be 
an indication of an injector gone bad.  The trip computer calculates fuel usage based on what the injectors are supposed 
to be flowing, not what they actually are flowing, so when an injector jams open or starts leaking the fuel mileage goes 
to hell while the trip computer still thinks everything is fine. 

If you suspect there is a problem with an injector, John Keppler suggests you use a stethoscope first.  “I started the 
engine, then using a mechanic's stethoscope, listened to each injector.  I could hear every one loud and clear except 5A, 
which was dead silent.  I found the bad injector in seconds with a mechanic's stethoscope.” 

If you have an injector that doesn’t seem to be working, pull the connector off and check the windings with a VOM.  
The windings on an injector should measure 2.4Ω at room temperature, and must not be shorted to the injector body. 

You could get lucky like Keppler did.  “I pulled the plug on my 5A injector and measured its resistance.  The cheap 
meter I was using read 2.9 ohms.  That looked reasonable.  I then measured the voltage across the plug contacts with 
the engine running.  I can't remember the voltage I got, but it was identical the the 1A connector (the most accessible 
plug to use as a reference).  At this point, I plugged the injector back in and started the engine.  With the stethoscope I 
could tell that it still wasn't working.  Then I tried tapping 12 volts directly across the injector.  The injector clicked!  
Loud and clear!  So I once again plugged in the injector and started the engine.  This time, I could hear it working just 
fine with the stethoscope, and the engine ran smooth.  I can only assume that I either had a bad contact at the plug that 
got cleaned up by repeated unplugging and plugging, or the injector was just plain stuck, and hitting it with a good shot 
of 12 volts freed it up.” 

If you’re not as lucky as Keppler, purchase one of the many fuel injector cleaners available that can be added to the gas 
tank.  The common advise on how to use in-the-tank injector cleaner is -- as concentrated as possible.  Run the car 
down to 1/4 tank, then add the injector cleaner, then run it down to nearly empty before refilling. 

If that doesn’t fix the problems, the next step is to take the car to any place that specializes in fuel injection work.  They 
can flush the injectors with a cleaner by just connecting a line to the fuel supply line and running the engine. 

If this doesn’t work, the next step is to depressurize the fuel system, disconnect the supply and return hoses, remove 24 
nuts and remove the rack of injectors as a unit.  Take it to the same fuel injection shop and have them flush it in a rig.  
With it separate from the engine, they can use much more powerful cleaners than they can on the engine.  Best of all, 
even if their cleaning doesn’t fix the problem, they will be able to tell you if any injectors are bad and which one; they 
can actually watch them spray on the bench. 

 
 

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If you’re the adventurous type, you might try testing the injectors yourself.  Unbolt the set from the engine and raise 
them up a few inches while leaving the fuel supply and return hoses connected.  Jumper the relay in the trunk to allow 
operation of the fuel pump with the engine off.  Immediately check that no injectors are dribbling fuel.  Place a small 
glass jar around one injector.  Connect a couple wires to this injector, and give it a quick zap with 12 volts.  Note: do 
not leave 12 volts connected continuously; only give the injector instantaneous jolts.  Observe the performance of the 
injector.  Repeat for all injectors; you can empty the glass jar back into the tank between tests.  Obviously, any injector 
that seems to perform differently than the others is suspect.  No smoking is suggested during this procedure, and it 
would also be wise to avoid electrical sparks. 

Tony Gardner reports that J. C. Whitney offers a device for doing such tests called an Injector Inspector.  “This device 
is hooked up to the battery and one can select various combinations of pulses to operate individual injectors.  They 
suggest using it with the injectors in-situ and timing pressure drops but I did not find this very convincing.” 

“Back lighting with a flashlight is helpful.  You can also rig the device to facilitate pumping cleaner through each 
injector.”  If you can devise a pressure container with one line in the top and another out the bottom, you can fill it with 
flushing fluid and connect the fuel line in the top and let the fuel pump push it through the injectors. 

The injectors can be replaced individually, and there is nothing wrong with replacing only the one that’s gone bad.  
Replacing the whole set is expensive, and usually not warranted. 

The only differences between injector part number  0 280 150 163  (1985-91  front  two), and 0 280 150 164 (1985-91 
rear ten) is the length of the piece of hose attached to them.  These injectors were fitted as a recall to cars with injector 
part number 0 280 150 105 (1980-85), so those injectors have no functional difference either. 

The D-Jetronic cars had either 73143A/0 280 150 023 or 73143B/0 280 150 035 injectors.  Some reports indicated that 
the last three digits indicate an orifice size difference, but Roger Bywater of AJ6 Engineering assures us that the 
number reflects a minor design change only and that all of these injectors have the same flow specifications.  Note that 
the D-Jetronic injectors do not have the same flow rate as the Digital P injectors. 

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

 

“New smaller lighter fuel injectors allowing the fitment of a lower mounted fuel rail, giving improved control of fuelling 
at small pulse widths.” 

Fuel injectors tend to be blamed for a lot of problems, probably more than they actually are responsible for.  Michael 
Neal (Jaguar mechanic) says:  “The only failed injectors I have seen have been from running water through them or 
running a car with a blown head gasket to death.” 

 

FUEL INJECTOR PULSE CHECKING:  Robert Dingli suggests “an oscilloscope or a smart DVM with pulse width or 
duty cycle readouts can be used to check the injector electrical supply.  Some modern ECU’s can detect whether an 
injector is unplugged (or short circuited) and thus it’s best to connect the electrical apparatus in parallel with the 
injector.”  Michael Neal says the injector pulse width should be around 3 milliseconds at idle. 

John Keppler suggests you could go with what you have and check the injector pulse with an old-fashioned dwell 
meter.  Hey, you’re not using it anyway; if you still have any cars with points, it’s high time you installed electronic 
ignition modules in them.  Keppler points out that a dwell meter is merely a 12V duty cycle meter with scales in 
degrees instead of 0-100%.  Disconnect one injector connector and connect the two leads from the dwell meter to it -- 
which may require sticking some small flat metal things into the plug.  Ideally, buy a new Bosch plug and create a 
jumper to connect the dwell meter while leaving the injector connected.  Fire the engine up and see what happens.  
Remember to check both circuits (there are two, one per bank on the H.E. and all mixed up between banks on the pre-
H.E.). 

At this point, I cannot offer any guidance on just what kind of readings to look for.  Remember that, while point dwell 
should stay relatively constant with RPM, injector pulses will indicate a “dwell” that varies with engine RPM and load. 
 Just check the dwell meter readings on someone else’s car as a basis of comparison; it probably doesn’t even need to 
be a Jaguar, since pretty much any fuel injector should be seeing the same kind of injector pulses. 

 

 
 

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INJECTOR SEALS/NOISY FUEL INJECTORS:  Each injector is mounted with two rubber rings, a small one at the 
tip and a large one around the body.  These rubber parts isolate the injector from the manifold.  There are two reasons 
you might want to replace your injector seals.  The first is noise; Hunt Dabney says:  “On the noise issue, I just replaced 
all of the injector seals and rubber mounts.  My injectors are now really quiet!”  The other reason, of course, is to 
eliminate vacuum leaks; the smaller ring at the tip is obviously critical for sealing the intake manifold, but the larger is 
also important for holding the injector securely against the smaller. 

Frank Perrick points out that these seals are available at any auto parts store since they are standard Bosch items.  The 
seals come in packages to service four injectors, so you will need three kits for the V12.  Here’s a tip for getting the guy 
behind the counter to get you the right parts:  When he types all the make and model data into the computer, one of the 
screens he will face is where he must select the type part you’re looking for.  One choice is “fuel injector/carburetor 
gaskets”, but if that selection is made it will come up with some obscure part number and claim it’s not available.  If, on 
the other hand, he selects “fuel injectors”, it will come back with a listing for the “fuel injector seal kit”.  Or, Perrick 
suggests you can just carry an injector in there and say “I need these gaskets”. 

John Napoli found a different kit: “Standard Motor Parts SK-3 does the trick -- handles four injectors (eight rings -- 4 
big and 4 little) for less than $4.00 US.”  A similar kit, the one carried by AutoZone, is GP Sorensen part number 800-
9207.  The kit offered by Discount Auto Parts is Tomco part number 27013. 

However, not all kits are the same; some carry parts besides the two rubber rings.  One such kit is Beck/Arnley # 158-
0021 vp 1; B.J. Kroppe says, “The kit included the small, square-sectioned seal between the injector tip and plastic cup, 
as well as the large rubber washer which I believe isolates the clicking injector from the rest of the engine. The last bit 
that was in the Beck-Arnley kit was the tiny (nylon?) mesh filter that fits into the top of the injector fuel inlet.  This is a 
neat design.” 

Kroppe also found a set from Python Injection, Incorporated, part number 200-120, with even more parts.  
“Description:  large injector washer (isolator), square section o-ring seal, mesh injector inlet filter, injector tip cup (does 
not fit Jaguar injectors).” 

You might wish to make the extra effort to find seal kits with pintle caps -- see below. 

 

FUEL INJECTOR PINTLE CAP:  You can’t see this thing when the injector is in place, since it is on the end buried in 
the intake manifold.  When you take the injector out, though, it is the plastic cap that completely surrounds the injector 
with a hole at the tip where the pintle is.  The original pintle caps are a tan color, and reportedly not very reliable; 
you’re likely to find them damaged.  Richard Chapman says, “I got black caps in my seal kit, along with the 2 rings.  
Just pulled off the old ones with pliers and a twisting motion - not too difficult, just a bit nervous on the first one.  I 
could not have reused the old caps once removed.  It was difficult to get the new ones to fully seat inside the recess 
where the injector tip meets the injector body - lots of fiddling needed except on the 2 different ones which fitted with 
ease!!!  Weird.” 

Paul Hackbart says, “The pintle caps are not for spray pattern but for heat protection.  To replace them I used a little 
mm socket so not to damage the solenoid tip and tapped it back on to click into place.  I would replace the pintle caps 
regardless.  When I did mine, 3 or 4 were cracked and most of them at the end were missing.  The original orange ones 
are not recommended as all pintle caps by Bosch are black/heat resistant.” 

 

IDLE STUMBLE:  A stumble may be a sign of an intake manifold leak.  Since the EFI senses manifold vacuum and 
meters fuel accordingly, it would make sense that an intake manifold leak would only cause a high idle, not a stumble 
or misfire.  However, a manifold leak that is near the intake of one particular cylinder apparently has more effect on that 
cylinder than on others, and can cause an individual cylinder to run lean.  This may be quite serious, since a lean-
running cylinder is a candidate for a dropped valve seat -- a very expensive problem.  If a leak is suspected, a can of 
WD-40 makes an excellent leak locator; simply spray on each area while the engine is running and see which spot 
makes a difference when sprayed on.