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XJ6 Engine and Transmision

// Jag-Lovers // The Jaguar XJ6 // Contents // Index //


Jaguar XJ6: Engine and Transmission

Belts and Pulleys

As I recommended earlier, all the belts should be replaced every two years, or if it is only 18 months since the last replacement and you are planning a 3,000 mile trip. Never start on a long trip without near new hoses and belts. Every time I have done it I have regretted it. The extra strain of 6 to 8 hours of continuos driving daily will finish off weak hoses and belts in short order and it is no fun to be spending your vacation under a car on the side of the road or spending your vacation money on a tow truck and garage fees.

Belt Tensioners

One really nice thing, about at least the Series III (hey folks, I own a Series III and that is what I go look at when I need help on writing this book) is the way the various accessories are adjusted to get the belts tight. The screw adjustable tensioners beat the heck out of the normal US type of tensioner where you have to use a pry bar and three hands to adjust the tension.

Alternator Belt

The only one that is difficult is the alternator belt which is only accessible from beneath the car and for which the range of acceptable belts is very narrow. For the alternator belt I suggest that you check the adjustment position on your old belt then decide if you can use a shorter or longer belt. Remember, you will have some stretching in the first couple of months of usage, so aim short. This way when you find out they don't have just the right belt you will know which way to go to get the next size. In the case of the alternator belt, always carry the old belt with you so you can compare the length at the counter before you walk out!

Removing Belts

The belts can be removed and replaced without removing the fan shroud or the fan. It takes a bit of twisting and threading to get the belts around the fan blades but it can be done. If you are replacing the belts and already know you have the right belt in hand or have transportation while the Jaguar is down so that you can go get another if you have the wrong one (the automotive equivalent to not painting yourself into a corner or sitting on the branch you are sawing off), you can just cut the old belts and pull them out the easy way. Then you only have one set of belts to snake in around the fan blades.

Water Pump

The water pump is a readily available item in most big cities in the US. It ain't cheap, but it is available. Replacing it is, again, straightforward. The hood (bonnet) is the only problem here and it can be handled as it was in the previous section on the radiator replacement.


I recommend that unless you are into pain in a big way, i.e. you sleep in leather with a whip beside the bed, take your car to an alternator shop to have the alternator replaced. Usually they will do it for free if you are buying the alternator from them.

Removing the Alternator

If you do replace it yourself, be forewarned that it must be done from under the car and it will probably be covered with dirt and lots of oil from that front seal that was made to leak by the designers as an anti-rust system... I will never again do one myself, it just isn't worth the blood, sweat and tears.

Starter Motor

In Lawrence Buja's appendix on Starter Diagnostics at the end of this book you will learn more than you ever needed to know about diagnosing starting problems involving the starter.

Timing Chains

Here we are into the engine itself, the timing chains. There are both an upper and a lower timing chain. These items are so inexpensive that I have a new set on the shelf ready to use if I ever need them. This will probably protect me from ever having to replace them. Murphy's Law always says that the part you don't have or can't get or is most expensive is the one that will break. These are cheap and easy to get.

Lawrence Buja has had some experience with a broken timing chain.

Worn Tensioner

The first indication that you have a problem will be a noise from the front of the engine. If the tensioner becomes worn or becomes dysfunctional you will hear the chain slapping around. If it gets loose enough the valve timing will be affected such that the car does not run smoothly.

The Cylinder Head

One of the weak points of the 6 cylinder engine is that the valve tappet followers will eventually loosen up so that they do not stay seated in the head. It is an easy fix and should be done before they start slipping around.

If the tappet follower come loose there is a ticking noise from under the cam covers. The sound can be likened to the sound of a sewing machine. Oddly enough I have heard people say, "Its so smooth, it sounds like a sewing machine." In this case, that is not good. A loose follower can cause all kinds of damage to the engine, mostly in the head.

Stakedown Kit

Many XJ6s have had the stakedown kit installed already and you can tell if yours has one by reaching your finger deep into the oil filler hole on the cam cover and if it is there you can feel it. I must admit I could not find it when I felt, but a mechanic friend of mine felt and assured me it was there. By the way, don't try this if the engine is warm.

A stakedown kit will run about US$300 installed at 1995 prices. It is a cheap piece of insurance. If it hasn't been done, do it before you trash your engine!

For more information you should read both the Stakedown FAQ and Gunnar Helliesen's experiences.

Head Removal

From Julio Loza I received the following advice on removing the head when it is stuck.

While rebuilding the cylinder head (it was warped and leaking water to the cylinders) I found the studs frozen in place. No matter how hard I tried I could not pull the head off with the studs on. I tried soaking them in various solvents to dissolve the rust but to no avail. At the suggestion of the local Jaguar shop, I tried an impact wrench to 'loosen' the studs but this did not work. Here is what a friend suggested and worked:

  1. Buy a few of the nuts that fit the studs. (I got mine at PepBoys.)
  2. Take two nuts and tighten them on one of the frozen studs.
  3. When they are both in far enough, take two wrenches and try to undo the bottom one while tightening the top one. You are basically compressing the two nuts against one another.
  4. Once they are as tight as they will get, try undoing the bottom one only. This may require a long pipe to get enough torque. If the nuts are tight enough the frozen stud should begin to turn. If the top nut begins to turn instead, tighten them more.
  5. This procedure took all of the studs off and none were damaged. After a couple of uses, the nuts will begin to strip and need to be replace with new ones. This procedure will only take an hour or so and will make the removal of your cylinder head a lot easier.

I had a head stick on a 1968 420. We took all the nuts off then squirted WD40 into every nook and cranny. Then we hooked a hoist to the head as though we were going to remove the engine. We lifted the car so that the front wheels were 2 inches off the ground and let it hang. Every day we would squirt in more WD40. After three days the head slipped off and the car came down with a thump.

Head Performance Improvments

While we are on the subject of the heads, there is a lot of work that can be done here to improve the performance of the XJ6, especially the Series I and Series II versions. By the time the Series III came out the head had been very much improved from the Mk VII head from which it evolved.

I have heard it said that you can gain 50 hp just on head improvements alone.

Exhaust Valves

The exhaust side of the XJ6 head is just about as good as you need it to be no mater how radical you get on improving the engine. Some of the D-type heads had huge exhaust valves by comparison, but they are not necessary. There is little to be gained on the exhaust side, so spend your money on the intake side where it can use some help.

Porting and Polishing

The first thing you want to do is the porting and polishing. You do this first so that the crap and dust that it creates will be washed away after the machine shop does their job. You don't want it getting into the new valve guides and other goodies you will be adding later.

Porting and polishing will make the biggest single difference on the heads of an XJ6.

You have two levels that you can aspire to in porting and polishing. The first level is to just smooth out the intake ports so that they are smooth and without lumps and casting imperfections in the walls. Finish the job with 80 to 100 grit sanding drums. This is probably all you will want to do for a strictly street machine.

Polishing is probably not done on a street machine, but if you are into racing then you want to polish the ports down to a 1200 grit sand paper. They should be almost a mirror finish when done. This has to be done gradually from the 80 grit in the first step to the 1200.

Enlarging the Ports

If you are into racing you may want to enlarge the ports to just under the size of the gasket openings. Enlarging the ports on a street machine just hurts the low end performance.

You can do this by placing a gasket against the head and marking the openings on the head. Then enlarge the ports to about 1/16 inch smaller than the gasket openings. Be careful though as there are water passages in the head and they are closer to the surface as you approach the valve seats and if you cut too deep you could be in big trouble. The cut is mostly at the port and should taper off quickly toward the valve seat to prevent disasters.

Smoothed Valve Guides

There are several improvements that can be made by the machine shop that cost very little. First, the valve guides that stick out into the fuel flow can be smoothed flush with the port wall. This will improve the fuel flow immeasurably.

CC-ing the Head

Having the heads "cc'd" will make the engine smoother and there may be an increase in power. You can do it yourself. Place the head on its back with the spark plugs installed and the valves installed Then make sure the mating surface where the head meets the block is level. Now fill the depressions in the head at each cylinder with light oil till it is level with the gasket surface. Use a syringe to remove the oil from each depression and measure what you take out very carefully in a graduated container. Write down the number for each cylinder. What you want to do now is to take your Dremel tool and sand away enough material from the inside of the head so that all the cavities are as large as the one that held the most oil. Do not grind on the one that was the biggest! You should remove the material evenly around each cylinder head. When they are all the same size you are done. Your head has been "cc'd." With all combustion chambers the same size the engine will run smoother.


The racing engine should have the heads glasspeened to relieve stress. You can do it on any engine and it is inexpensive.

Bigger IntakeValves

Increased size on the intake valves can improve even a street car, and they are almost mandatory for a car that will be raced seriously. The intake valve size on a Series III XJ6 is 1-7/8 inches. This is a good size for street use and the valves are stock Jaguar items so are easy to get. The early XJ6 had 1-3/4 inch intake valves and increasing to the 1-7/8 inch Series III intake valves will improve these engines. It is possible to increase the valve size to 1-15/16 inches without changing the size of the spark plug. If you go to a 2 inch intake valve you will have to change to a 10 mm spark plug. You should not go to a 2 inch valve unless you are seriously racing the car.

Improved Carburation

Remember though that with the stock dual carburetors on Series I and II cars you will gain nothing with the big intake valves. The big intake valves require more breathing room, like 45DCOE Webers.

The best compromise for a street car is the 1-7/8 inch valves of the Series III with improved carburation. In the Series III of course, there is nothing to do as it already has this capability and the EFI to feed it.

Valve Springs

While you are doing this valve work, plan on replacing all the valve springs. You will be putting in a hotter cam and the stock valve springs will float at 5500 rpm. There is no reason to do this much work and then scrimp on costs. The new valve springs won't cost that much. Use a stronger set of racing springs and you will then be able to use a hotter cam without valve float.

Valve Spring Retainers

If you are racing the engine you will want to replace the stock steel valve spring retainers with the lighter weight alloy retainers. On a street head, these will do nothing for you, but at high revs, 6000 rpm and up, they will make a difference.

Bronze Valve Guides

Replace all the valve guides. You don't want to waste all this time then find that you have to replace a valve guide in the near future. The head is off, so replace the guides now. Use bronze valve guides as they lubricate the valve stems better and will last longer for that reason.

Triple-Angle Valve Seats

Considering the cost vs the improvement, one of the cheapest things you can do is to have the shop cut "triple angle" valve seats when they install the new valve seats and valves.

Hardened Valve Seats

The new valve seats should be "hardened" seats so they can withstand the rigors of unleaded gasoline. Even if unleaded is not mandatory where you live now, it probably will be someday so get a head start on it now.

Valve Lapping

I recommend that you do your own valve lapping, the last step in this head restoration/improvement. The shop will not spend the necessary time to do it right and you will because you know that its your money down the drain a year from now when you have a burned valve and your compression is down.

First Piston and Cylinder

There is not alot to say here except to praise the quality of the XJ6 bottom end. The main and rod bearings are very tough and will last forever. It is a testament to their strength when you consider how many horsepower can be coaxed out of this engine without any change in the bottom end at all.

High Compression Pistons

Some owners will try to get more horsepower from their engines by increasing the compression ratio by using high compression pistons. This is not really necessary and it makes it hard to run on the fuels available at the pump without causing damage to the engine. Here is where you can damage the bottom end. If your compression ratio is too high and the car "pings" you may not notice it and it will be beating your crank and bearings to death.

You can gain more at lower cost by reworking the head and changing the cams and you will do it with less possibility of causing damage to the engine.

Engine and Transmission Conversions

Wow, here we are at the transmission interface! Here is where all the controversy begins, or maybe ends if you are talking about the "chebby lump."

V8 Engine Conversions

Johns Cars in Dallas Texas makes conversion kits to replace the entire Jaguar engine with a Chevrolet V8. For myself, I wonder why one would do that since the cost of the conversion and the later cost of the worse fuel mileage will cost as much as overhauling a Jaguar 6 cylinder engine. At the time of this writing the cost either way is about US$3,000. Is it more reliable than the Jaguar 4.2 liter 6? I don't think so. Jaguar engines are reliable if cared for as are most engines no mater what their origin. What about top end? No, a Jag can keep up with it. Acceleration? Well, here you have me, probably so. But it seems alot of money to get a little acceleration.

Bruce Bowling is one person who thinks the conversion to V8 power is a good thing.

GM TH350 Transmission Conversions

A similar kit from Johns will allow the replacement of the Borg Warner BW66 automatic transmission with a GM TH350 transmission but retaining the Jaguar engine. This conversion makes sense from every direction.

For the purist, remember that Jaguar didn't make the BW66. If they had it would have been beefy enough to handle the power from the Jaguar engine. It isn't. Besides Jaguar obviously liked the GM TH since they put the TH400 into the XJ-S. And you cannot tell from the outside that it has been done unless you look carefully at the back of the engine and see the 1 inch thick aluminum adapter plate.

For those that want to pull any kind of trailer it is almost required. I tow a race car on a trailer behind my XJ6 and I would never be able to do that with a BW transmission.

From the reliability standpoint, there is just no contest.

From the cost standpoint it is also no contest if your BW 66 is not repairable. If your BW is trashed and you need a new transmission it will cost about US$2,000 to buy the new BW 66 and install it at shop labor costs at the time of this writing. (To rebuild the BW66 will cost about US$850 in 1996 at Pauls Discount Jaguar Parts. There may be others who can do it as well.) The price of a new one is almost the same for a conversion and a TH350 transmission. The payback is 5 years down the pike when you need an overhaul or a new transmission. The TH350 can be had almost anywhere in the world for 1/3 the price of the lesser BW66. If it were just availability it would not be a good swap, but the transmission is much better and cheaper at the same time. I found that my highway mileage improved slightly with the TH350.

GM 700R4 Transmission

There is another kit that will allow the importation of the GM 700R4 transmission which has an overdrive gear. Real nice if you are on the road alot. I have no experience with this one so can't comment on it except to say if I had known about it when I put in the TH350 I would probably have gone that route.

Toyota 5 Speed

From Dellow in Australia there is a conversion bellhousing that can adapt the Toyota 5 speed manual gearbox to the XJ engine. If you are souping up the engine to race specs, this makes sense. I have heard that the top end gear on this box will get you up to around 150mph if you have the horsepower. That would be a fast XJ6.

The 5 speed box is available in the US and I am sure anywhere Japan has sold cars at a very reasonable price from the junkyard (breaker). In 1995 I found on in good shape for only AUS$100.

The conversion will likely make the car look different because of the different location of the gearshift knob positioning and it will require some cutting on the transmission hump. But if you are racing just a little it would be very nice.

Jaguar Manual Transmission

I understand there is also a Jaguar manual transmission that can be fitted at a somewhat higher price.

BW Auto Transmission Fluid

If you are still running a Borg Warner unit, Tom Graham sends this information on the fluid to use:

There are varying opinions re whether to use Type F or Dexron. (A lot of Jag mechanics around here like to use Dexron because it gives a softer feeling shift). The Jag manual says Type G. I think we had an answer that Type G is same as Type F. Also, our local Jag club sent a letter to Jag HDQ in Mahwah, NJ with just this question. They responded with, use Type F in BW 65 and 66.

Auto Shift Linkage Cables

While on the subject of the transmission, the following comments apply whether you have a Borg Warner or a GM transmission. The shift linkage on an XJ6 is a flexable cable with a rather thin rod at the end that pushes and pulls things around. If you park on a hill, expecialy with the nose pointed up, do not use the Park position to hold the car. Always set the parking brake first, then put the transmission into park so that there is no pressure on the interior transmission pawls. If you don't you could bend the shift rod as you try to pull the transmission out of the park position. The cost is beyond belief to repair this. The labor in 4 hours and the cable is not cheap either. Then there is the tow truck fee to get your car to the mechanic since you will not be able to get the car out of park once the rod is bent.

Oil Pressure Sender

The oil pressure sender is infamous for its inaccurate readings. This item is a very expensive sender at the dealer. After my first edition of this book hit the stands I recieved a phone call from one of the dealers listed at the back of the book telling me he could supply it for 60% of the price the Jaguar dealer was asking, so look around. Inside the housing is a wire wound resistor that has a wiper connected to it from a diaphragm that measures the pressure. The diaphragm is moved by a piston that can get stuck with crap from dirty oil. If this happens you may get a flat topped reading that hits a peak and goes no higher or it may get stuck so that there is a reading of pressure when the engine is not turning. Sometimes cleaning out the input end with a blast of pressurized air will make a difference, but usually it won't.

The wire on the wire wound resistor will wear and after many miles will either break or will begin sliding around on the form. When this happens you will get very quirky readings, sometimes high, sometimes low. If you start getting low pressure readings and the idiot light is not confirming the low pressure, this may be the problem.

Replacing the Sender

If you go to the parts house and they tell you they have a pressure sender for your Jag and it seems cheap, they are talking about the pressure sender for the idiot light. It is cheap, but it won't work in the gauge. You can tell the two apart as the light sender is only about 1 inch in diameter and 1.5 inches tall. The pressure sender for the gauge is about 3 inches in diameter and 3 inches tall and looks like a small tuna can fitted to a piece of pipe with an electrical connector on the other end.

This item is expensive and not readily repaired so the only alternative is to bite the bullet and get one from Jaguar or one of the suppliers in the back of this book. The one consolation is that it will probably last another 70,000 miles.

One of these days I am going to attempt a repair on one that has had the wire break. I will report the results in this book, but I doubt that it will be economical, it will just be to see if I can do it.

Engine Oil Pan

The oil pan is another place where things go wrong. Being of cast alloy it is soft and many a PO (Previous Owner) has tightened an oil pan plug too tight and stripped out the threads. One car I bought, the PO had used epoxy glue to glue the plug in place and then he changed oil using a pump. Of course he neglected to tell me this when I bought the car.

There are several ways to solve this problem. All have their advantages. All are relatively inexpensive and all of them work.

I have already mentioned the pump thing so I will skip it. Besides, I don't see any real advantage to that one. The next possibility is to put a helicoil into the old threads to rebuild the threads to accept the old drain plug. This works sometimes, if there is enough material around the hole to do the repair. It usually requires removing the oil pan which on an XJ6 requires removing the engine from the car.

The second method is to drill out the hole to a larger size and retread it. Again this requires removing the oil pan since you want to be able to remove any metal chips so they don't get swept into the engine oil passages.

There are rubber stoppers that expand into the threads when a bolt is tightened they are sometimes available in the parts stores. I don't like this solution since oil and rubber don't really mix and I would be suspicious of how long the rubber could handle the heat of the engine oil.

Quick Drain Oil Plugs

The best solution I have found is to install one of those "quick drain" plugs. The ones with either a remote trigger or with a lever on the plug that allows you to drain the oil without removing the plug. This way you can put a good grade epoxy glue on the plug when you install it to glue it in permanently and yet you can still drain the oil when the time comes. I like the remote trigger type and consider installing those even if I didn't have a problem to begin with. Its alot more pleasant to change the oil if you don't have to crawl under the car, not to mention, alot safer, since a Jag is so low you have to jack it up to change the oil.

Spark (Ignition) Coils

From Gregory Andrachuk I received the following advice on spark coils:

The faulty or fault-prone coils are not the Lucas coils, but the Ducellier coils made in France. My 1982, in fact, has a Ducellier coil which I presume is original, and it operates perfectly with no leaking of oil. I think the failure is an oil seal failure to begin with. My coil has an internal ballast resistor, or so I assume, since there is no resistor mounted beside it as on other cars I have seen. I believe that the DLC 102 coil used as a replacement requires an external resistor, but the sales reps don't seem clear about this. I think one should suspect coil trouble with sudden engine misbehavior, but replacing perfectly good coils seems unnecessary.


The distributor is just a standard points and condenser type of distributor on the Series I. (The Series II and III used contactless electronic ignition.) It is adjusted in the normal way with a screw driver to loosen the arm and to pry the points apart or together and a feeler gauge to measure the gap.

It needs to be lubricated on the pivot post, through the base plate opening at the cam and on the center screw with a dab of engine oil. On the cam it should be lubricated with grease or Vaseline.

Vacuum Advance

There is a vacuum advance diaphragm on the side. The most common failure of this part is the rubber vacuum hose that connects to the advance diaphragm. The rubber deteriorates with age and starts to leak so that there is no advance as the engine reaches cruise speed. This can cause overheating and loss of economy by running the engine in a constantly retarded condition. If the hose is OK you can check the advance by putting the ends of the hose in your mouth and sucking. This should cause the distributor points plate to rotate slightly as you watch it with the distributor cap removed. If it doesn't rotate and the hose is good then there is a bad diaphragm in the advance mechanism and it needs to be replaced.

Setting the Timing

The coarse timing is set in the usual way by first removing the #6 (the front cylinder) spark plug and turning the engine by hand until the compression stroke can be detected by the pressure escaping around your thumb as it is held over the spark plug hole. Now continue rotating the engine in the same direction until the appropriate timing mark is in alignment with the timing cover pointer. The correct direction to rotate the engine can be easily determined by looking at the fan blades. The engine rotates such as to make the fan suck air through the radiator, i.e. the fan rotates so that the leading edge of the blades are the edge to the front of the car toward the radiator. Now set the vernier screw to the center of its position. Then loosen the distributor clamp so that the distributor can be turned stiffly. Set the distributor timing as close as you can get it while using a light across the points to detect the opening of the points. You want the points to just open. Clamp the distributor in this position. The car should now run well enough that you can continue with the fine timing.

The fine timing adjustment is a knurled nut on the opposite side of the distributor from the advance diaphragm. To adjust the fine timing a timing light (strobe) is held on the crankshaft damper timing marks and while watching the alignment of the marks with the timing cover pointer the knob can be adjusted to fine tune the spark timing.

Engine Oil Filler Cap

Also here is the filler for the engine oil. The engine requires almost 9 quarts of oil when changing the oil filter. To an American who is used to all engines requiring 4 quarts, this is one hell of a lot of oil. On the other hand with an engine that leaks oil like the 4.2 does it may all be needed. The interesting thing is that if it falls only a quart low it will trigger the low oil pressure light on hard deceleration or hard cornering. Generally this is not a problem as long as the condition only lasts a few seconds. The crank and rod bearings are not supported by oil pressure, they just ride on the surface of a molecule thick layer of oil so as long as the pressure comes right back up no harm will be done. But... you should correct the problem as soon as practical and try to refrain from extreme maneuvering until it is corrected.

Engine Oil

I recommend using a synthetic oil. I had a mechanic once tell me that if I used synthetic oil it would cure the oil leaks. I didn't believe him, but since I knew him to be a good mechanic, I tried it. It worked. I don't know why, but it worked. The reduction in lost oil and the fact that I could leave the oil in for three times longer before changing it made up for the increased cost. I now use only synthetic fluids throughout the car.

Low Oil Pressure

Jaguars are often asked to run with low oil supplies (they leak the stuff out) and on turning corners it is not unusual to see the oil pressure light flicker. This is not good and should be attended to, but it never seems to damage the bottom end of the engine to have these temporary losses of pressure.

You may have heard that Jaguar considered going into the manufacturer of refrigerators at the end of the second world war but they changed their mind when they couldn't figure out how to make them leak oil...

Fuel System

The carburetors and EFI are in this area also. The Series I and II cars are carbureated while the Series III has Electronic Fuel Injection (EFI).


The carburetors require very little maintenance. Keeping the fuel screen clean and topping up the oil in the dampers is all that is required. Some books recommend using SAE 20 engine oil for this purpose. I have used automatic transmission fluid, olive oil, corn oil all with no noticeable difference in performance. Be forewarned that if you use corn oil and spill some on a hot engine part it will smell like you are making popcorn and will keep you hungry whenever you drive.

Electronic Fuel Injection (EFI)

EFI requires even less maintenance than the carbs. The only maintenance I have done on my '82 XJ6 EFI in 70,000 miles was to replace the injection hoses that the PO had installed. The injection hoses, the hose from the fuel distribution rail to the injectors * be of high pressure type. It looks just like the standard fuel line, but don't use standard fuel line, it won't last. The system is under very high pressure and the hoses will begin to leak very soon if you don't use high pressure hose designed for fuel injection systems.

EFI Fuel Leaks

The first indication (hopefully) that you have a leak is a smell of fuel when you stop the car at the end of a run. The hoses will be leaking onto the top of the head and the heat will cause evaporation that you will smell as soon as you walk around to the front of the car. Don't ignore this or you may have an under hood (bonnet) fire which will really ruin your day. Replacing these hoses is easy and will only require 45 minutes to do all 6 of them. The main thing to remember is to tighten the clamps so that they don't leak under pressure and don't tighten them to the point that they damage the hose.

You should open the hood (bonnet) on a regular basis right after driving the car to look at the hoses. They will be wet with fuel if they are leaking, but 5 minutes later there will be no indication as the fuel will have evaporated. Always replace all 6 hoses together so you know the age of the hose. Using hoses of mixed age just makes for more work in the long run.

JagWeb has more information on fuel smells inside XJ6 and XJ-S cars.

EFI Oxygen Sensor

On the exhaust manifold on the left side down low is the oxygen sensor. This item can affect your fuel mileage. If fuel consumption is high and you have not replaced the sensor in over 40 thousand miles, change it. The end of the sensor gets eroded away by the exhaust gas in 30 to 40 thousand miles and the EFI won't work properly unless the O2 sensor is working properly. A wrench, a pair of pliers and maybe some WD-40 is all it will take to do the job. When you install the new sensor make sure you use some anti-seize compound on the threads. The new sensor that you get from the parts store will have one wire coming out of the end of it. The box will include a connector so that you can snip off the old sensor and use the connector to put on the new one (after you have tightened it down!). If you connect it first you will not be able to twist it in without twisting the wire.

Sensor Replacement Light

The Series III XJ6s supplied to the US came with an oxygen sensor in the exhaust to help it run low emissions. The oxygen sensor light in the dash is tied to a circuit (which is in the trunk, by the way) that measures the miles since it was last reset. It is meant to be reset by the mechanic when the oxygen sensor is replaced. The idea is that your oxygen sensor is only good for 40,000 miles. Actually this is being optimistic. I find that mine needs replacement at 30,000 miles.

You should not use the light on the dash to tell you when to replace the oxygen sensor. You should instead use your fuel mileage and common sense. If you fuel mileage begins to suffer and you don't know why, pull out the O2 sensor and look at it. If the end is eroded away it is time to replace it. If you wait for the light to come on the sensor will have eroded away months before!

Resetting the Circuit

The problem most home mechanics have is that they don't know how to reset the circuit after they have replaced the sensor. The two manuals I have seen do not tell how this is done. If the light remains on it will deteriorate the housing from the heat and the light will fall out of the dash!

The reset button is in the trunk (boot) on the later models and is reset by pressing a recesed button in the unit. On earlier cars it is under the hood and is reset by a knob.

Transistorised Fuel Pump

In Rob Reillys appendix on SU Fuel Pump Modifications you can find instructions on improving your fuel pumps on Series I and Series II (non EFI) XJ6s.

Regular Checking

You should make it a practice to walk around the front of your car when you exit it at the end of a drive. Doing this just takes a little extra effort and it is worth the information you can gain. You don't even have to slow down as you walk by to notice such things as the electric fan running, the smell of fuel, the smell of hot antifreeze, the smell of a hot rubber hose, the sound of bubbling coolant in the radiator or the sound of steam escaping.

Catching these warning signs early will save you much grief. I recently saved myself from a big pain by walking around the front and hearing a hissing sound. I opened the hood (bonnet) to investigate and found a pinhole leak in a radiator hose spraying onto a hot engine. If I had not caught it early I would have had problems a week later and probably not in my driveway where it was easy to repair.


Next is the Front Suspension

// Jag-Lovers // The Jaguar XJ6 // Contents // Index //


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