Jaguar XJ6 SIII injector replacement
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Before starting work on any part of the fuel system, you have to relieve the pressure. The system is
pressurized to over 36 PSI in normal operations and unless there is a leaky part somewhere, it's
going to maintain that pressure long after the engine has been shut down. To relieve the pressure,
you want to find the "crash switch" in the door jamb on the right side of the dash. Simply pull
up on the little plunger as shown:
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Once the pump can't get power, we need to bleed off the fuel in the lines at the engine. To do this,
simply crank the engine with the key. It may even fire up for a moment but then it will starve for
gas and die. Now there is no pressure in the lines. There is still gas in the lines, of course, but
we can catch most of that and let the rest dribble. At least it won't be squirting at us under pressure!
NOTE: This method works on my 1985 US-spec XJ6, but it's possible that it won't work for
other years or especially other models (e.g. V-12 cars, etc.). Apparently the inertia switch cuts
off the ECU on some cars, which means the injectors won't fire to bleed off the pressure. Of course
it's possible that the starter is also disabled in these cases, so you'll know it didn't work. In
those cases, you'll need to instead disconnect the fuel pump relay on your car, then crank the
engine over to relieve the pressure. If your engine doesn't crank and fire briefly after tripping
the inertia switch, you should investigate further before assuming the pressure has been released
from the fuel rail.
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Let's familiarize ourselves with some of the major parts we'll be dealing with. Here's an overall view
of the right side of the engine, where we'll be spending the next couple of hours. (Well, OK, three hours
if you keep stopping to wash your hands and then take pictures like I was doing...)
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Now a couple of closer shots of the injector connections and the fuel regulator connections. The
electrical connectors just pull straight back off the injectors, though if you have something like a
dentist's pick to pull the clip wires in the shell away from the tabs on the injector it makes it
easier. And if you have old, brittle connector shells, then just trying to pull them off without
releasing the tension on the clip wires may break the shells. So be careful out there. The good
news on my car was that someone had previously replaced the rubber hoses to the injectors, so I
wasn't in imminent danger of sending the car up in flames. The bad news was the original "Cheney"
louvered hose clamps tear up the outside of the hoses, argh! So I'll replace all the hoses and
clamps anyway, as should you.
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We proceed by loosening all the big hose clamps required to remove the air filter horn off the front of the
air filter and the air filter canister itself. Then remove the big electrical connector from the AFM, remove
the 3 bolts that hold it into its bracket, and loosen the big hose clamps that hold it to the corrugated tube.
By lifting it up slightly you should now be able to slide it forward out of the bracket, and out of the car.
Then loosen the hose clamps that allow you to remove the intake elbow. After pulling the wires from all
6 injectors, things should look like this:
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Now we're ready to remove the fuel rail. At the rear of the fuel rail is the main fuel line connection.
Loosen the hose clamp and position a cut-off soda bottle underneath the joint. When you pull the hose off,
all of the gas in the fuel rail should slowly dribble back out the connection and into your bottle. A little
bit of gas might dribble out of the rubber hose, but if you park it off to the side open-end-up you shouldn't
lose much. (I put mine back under the cross-brace as you can see in the following picture.) I took a box
cutter and sliced the hoses connecting the injectors to the fuel rail, and the hose connecting the regulator
to the fuel return line, because I was replacing them anyway. If you plan to save yours this whole operation
will be more...um...interesting, because you have to pull a couple of different directions at once. One
thought might be to remove the clamp plates from the injectors and just pull them away still on the fuel rail.
But I wanted all that wonderful clearance to get at the injector clamp plates by having the fuel rail out of
the way. You need to remove the one bracket bolt (fine thread) near the regulator, and the two bracket bolts
(coarse thread) back by the throttle body. Those last two also hold the accelerator cable bracket onto the
throttle body, so that will come loose too; just put it off to the side a bit. Don't forget to remove the
vacuum hoses that go to the manifold and the fuel regulator. Now pull the fuel rail out of the engine
compartment. It will still be dripping some gas, so protect your paint as needed. Here's how things looked
after I had the fuel rail out:
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Now each injector clamp plate can be removed, along with its two injectors. Remove the nyloc nuts, two steel
washers, two nylon washers, then the clamp plate, in that order. On the front plate, the T-shaped bracket
takes the place of the two steel washers. Be sure not to lose the plastic spacers that go on the studs coming
out of the manifold; I just left them on the studs. Some of the plastic bushings on the tips of the injectors
may stick in the bores; even when you get those out, some of the hardened o-rings on them may stick in the
bores (though mine mostly stuck to the bushings). Make sure to get all of that out. When you get all the
parts off, here is what you should have:
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If you are the kind of person who really likes to dress up your engine compartment, now would be the
time to clean/buff those collars and clamp plates. (I'm not quite to that level on a daily driver
car, so I just put them back on like I found them.)
Here are the bores you can now see (note the plastic spacers on the studs):
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Here is a shot of one of those plastic bushings, along with its hardened o-ring (note the cracks in it.) Also
pictured for shock value is a new o-ring. I think it's safe to say that after 20 years, even if your
injectors are perfect, having been fed a constant diet of Techroline and having flawless spray patterns,
you still ought to remove them and replace all these rubber parts. Mine literally had the feel of bakelite
washers, not rubber o-rings. Just another of the dozens of sneaky places to look for vacuum leaks on an XJ6.
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Here is a single old injector and all of its old parts, taken apart and labeled with the part numbers. You
should absolutely replace the clamp collar bush, the pintle cap bush, and the insulator o-ring. Rebuilt
injectors should come with a new pintle cap and pintle cap bush, but you'll need to supply the other two
rubber parts (your rebuilder may be able to supply them for an additional charge, or you can buy them from
your favorite Jaguar parts source.)
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Here is where to find the part numbers on your injectors:
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One of the more obscure parts that will get replaced by a reputable injector rebuilder is the inlet screen.
No matter how much injector cleaner you run through your system, you aren't going to get hard particles out
that are trapped in this screen, and those simply build up over time. (Rapidly, if you have rusty tanks and
improper fuel filtration!) You can try banging the particles out by rapping an upside-down injector on a hard
surface, but far better to get the job done right if the injectors have a lot of miles on them. Here is one
of my old screens:
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Another benefit of a proper injector rebuild is the before/after information you get, so you can tell if there
really were problems before, and you can tell if your injectors really are well-matched and well-performing
afterwards. I had a spare set of injectors rebuilt, and that is what I installed in my car... and then I had
the original injectors rebuilt to put on the shelf as replacements for 100K miles or so from now. Here are the
results of testing and rebuilding those injectors. The first set is the one now running in my car:
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Here is a single injector all assembled and ready to be put back into the engine. I used a thin smear of oil
on the tip o-ring to make it slide into the bore more easily. Similarly, a light film of oil on the
hose barbs can help the hoses slide on more easily when we get to that step.
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Before we start reassembling things, it's worth having a look down in the throttle body. I mean, as long as
it's sitting there naked to the world. You should check the spacing if you suspect it's off, but at the very
least you should try to clean some of the gunk out of it. That's right were some of the crankcase fumes come
gooping back into the intake stream. Here is what mine looked like before I cleaned it:
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Using the old injector and regulator hoses as a pattern, cut your new fuel injection hose to the precise
lengths. Make sure you get fuel injection rated hose, because it's the only stuff that can handle the high
pressures. You should be able to get the hose and the special injection hose clamps (smooth, rolled-edge
style) at any good parts store. I took the easy way out and just bought a kit on ebay from that guy that
always has them for sale (I know, I know...) and of course the injection hoses were not all cut to the exact
same length so I regretted it. The hose you are looking for is spec SAEJ30R9, 5/16" (8mm) inside
diameter. On my car, the lengths were:
Injector hoses (all 6): 3-5/8"
CSI hose: 4-3/4"
Regulator hose: 1-3/4"
If you cut the injector hoses too short or too long, the fuel rail bracket mounting holes won't line
up right. If you cut them to different lengths, the rail distance will be set by the longest hose,
and all the other hoses won't reach across the gap enough to be fully on the barbs on both sides.
When it's all back together, you want all the hoses to be fully seated on their barbs, with the end
of the hose snug up against the rail or injector housing.
I assembled the hoses to the injectors (including the cold start injector, already bolted back into
its hole), also putting the upper clamp on each hose loosely. Remember to orient the clamps with
later serviceability in mind...and if you really want a professional look, make sure to get them all
facing exactly the same way. I then bolted each pair of injectors into their bores using a clamp
plate, then the nylon washers, then the steel washers (or T piece), then the nyloc nuts. Make sure
to get the clamp plate centered on the standoffs on the studs. Make sure to get the injectors
facing with the connectors upward, and centered in the intake holes and the clamp plate holes. Here
is what that should look like:
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Make sure to get the brackets facing the correct way around. Looking at the right side of the
engine, here is how they should be oriented:
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Here is a view with all the injectors in place with their new hoses and loose upper clamps:
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Now fit the fuel regulator hose onto the regulator on the fuel rail with two loose clamps, and install the
fuel rail onto all 6 injector hoses more or less simultaneously... making sure to get the regulator hose
started onto its pipe once the injectors are nearly home. You should be able to wiggle and push and get all 7
of those hoses fully home into their respective positions. Then you should be able to bend the CSI hose until
it can be started onto the fuel rail pipe. Once everything is wiggled, tugged, and threatened into position,
you can tighten all 9 remaining clamps (6 injectors to fuel rail, CSI to fuel rail, and both clamps on the
fuel regulator hose.) Bolt the fuel rail brackets back into place, remembering to fit the throttle cable
bracket pieces at that end. Reattach the main fuel line connection at the back of the fuel rail. Reattach
the vacuum lines to the fuel rail and fuel regulator. Plug in the injector and CSI connectors to the correct
injectors. Now it should look all nice and pretty like this:
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Now reinstall all those air inlet parts (elbow, AFM, air filter, associated crankcase breather pipe,
etc.) All that's left to do is to push the crash-switch button back down, then crank the engine to
life! It will take 10 or 15 seconds to refill the fuel rail, then it should start hard, then run
smoothly. (Some people prefer to put the car in "D" and turn the key to the start position for 5 or
10 seconds, then put the car back in "P" to start it normally. This should operate the fuel pump
without starting the car, and pressurize the rail without the 15 seconds of cranking. This method
depends on your starter interlock working properly though, so if you plan to do this, please
keep your foot hard on the brake pedal when you turn the key!) Be sure to immediately check the
engine compartment for fuel leaks from all those newly secured connections. (You *did* remember to
tighten all those hose clamps, right?) If everything checks out, then take it for a test drive and
marvel at the smoother idle, increased power, better gas mileage, less smoke under acceleration,
etc. Well, it did all that for me! Your results will vary depending on how bad your injectors were
originally. Mine were a little leaky, so the improvement was noticeable.
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