Fault Gallery

Please Note: The advice contained in these pages was given in response to individual letters sent to David Marks in his capacity as Technical Advisor to the Jaguar Enthusiasts' Club. As these are edited excerpts from written replies to such letters and their individual circumstances, such situations may not directly apply to your vehicle.

David Marks Garages can therefore accept no liability in the event of any unsatisfactory results through following this advice.

Please select an article:

XJS Tickovers & FansRadio Operation
V12 Pinks & PetrolAir Con in a Flap
Pinks Again. XJS StyleLow Brake Pressure
XJ4O ElectricsDead Circuits
Clean Sweep XJSLeaking Roof
Diff s/Arms & Manuals - XJRSCruise Control Non-Operation
Obscure Running ProblemsKangaroo XJS
Bulb FailureSucking Filler Cap
New shocksXJS No Cooling Fan
Smell of PetrolAll Buzzers and Lights
Fitting a pre-cat exhaust systemV12 Rattle
Brake Warning LightsXJS Leaking Windscreen
Locked Out - no VCMBlocked Drains
No Air FlowDouble Six Wiring
Dim-Dip System FailureInfo On Forties
Aftermarket AlloysIdling
Alarm ContactHeight Challenged
Pressure Fuel CapClickety Click
ABS Warning


XJS Tickovers & Fans

We recently bought a 1986 XJS V12. When starting from cold the engine revs up and down between 400 and 1.600rpm. This continues until the engine has warmed up. Once hot, it starts every time without problem. I have flushed out the cooling system. fitted new thermostats and changed all twelve plugs. The engine normally ticks over at 900rpm even with the idle speed adjusting screw fully in on the auxiliary air valve.

Incidentally the electric cooling fan comes on at the radiator when the dash fan switch is in any position but off, no matter what setting is used on the temperature control.

Paul Wingroe

Dave's Response: You are describing the classic symptoms of a sticking idle speed control valve, called the auxiliary air valve. This is located at the rear of the engine on the left-hand bank. You may be lucky if you remove the valve and clean it out with carburettor cleaner, and then alternate by immersing it in hot and cold water, you could shock' it back into working order.

If this fails, purchasing a new one is the only option. They retail at about £125.00 from Jaguar. The reason that your engine electric cooling fan comes on. is that it is designed to operate when the a/c compressor is engaged. and this can occur when either hot or cold air is demanded as part of the dehumidification process. I advise you to check if the fan is running only with the compressor and if the compressor is running all the time. You may have an a/c control fault, but trying to diagnose that by post will prove almost impossible.


V12 Pinks & Petrol

Having read the excellent article on leaded/unleaded fuels I am still a little unclear about my own 1986 V12. I have received conflicting reports on the issue from my local Jaguar main agent who claims I should have the ignition regarded. A recent letter in Autocar from Roger Bywater of AJ6 Engineering seems to agree with this. I have also noted a "rattling" noise from the engine under light throttle when pulling up a slight hill. This does not occur under heavy acceleration. Again the Jaguar dealer suggested that this may be pinking.

Donal Garland

Dave's Response: In answer to your query on unleaded, I feel I have stated my views in my article, and need not expand further - except to say that I run all my cars, ranging from a 1952 MkVII, via two pre HE V12 XJSs, a Sill V12 saloon and an XJ4O 3.6L to a S1 V12 saloon, on unleaded petrol and all at their original ignition settings. I experience no problems at all, but do maintain all the cars very carefully. The transient pinking could be one or all of many faults. These range from a weak vacuum or mechanical advance system, to reduced flow through the fuel injectors. If the latter is the case then ultrasonic cleaning of the injectors is the only solution.


Pinks Again. XJS Style

With my 1987 Vi2 XJS cabriolet, at steady speeds between 40/50mph if I accelerate very gently the car starts to pink. Harder depression of the throttle stops this or if I am going at a speed faster than 55mph, all is fine. So far I have stripped the distributor and checked the bob weight, replaced the dump valve, overhauled the injectors, fitted a new auxiliary air valve and new air con auxiliary air valve. Further a fuel injection specialist considered the problem was the ECU which is now off with AJ6 Engineering or could it be the vacuum regulator?

Peter Wignall.

Dave's Response: Many V12 engines seem to suffer from periods of transient pinking, and I will include my own in this group. It is normally (assuming that timing is correct, and distributor free etc) down to a faulty distributor vacuum advance system (decommission it as I suggested at the XJS seminar last year which understand you attended), low flow through the fuel injectors or maybe out of balance thermostats. You mentioned that you have had the injectors overhauled, and I hope that means ultrasonically cleaned and new basket filters fitted. Otherwise I would look at the other two areas before investigating the ECU.


XJ4O Electrics

My 1992/3 XJ4O 4.0-litre Sovereign appears to have some features not as standard:

My problem is that the engine cuts out. This does not seem to relate to time. weather, speed or type of driving. When it does cut out the dashboard shows the gearbox light and battery light illuminating. When re-starting the car starts immediately.

Steve Eveleigh

Dave's Response: There are no systematic procedures to follow for this sort of fault. We have come across this sort of fault a couple of times. and on both occasions it has been the fuel pump.

I say this on the assumption that your car has the fuel pump in the petrol tank, as opposed to under the car on the axle plate. which is as it should be according to the date of registration you have given. On occasion the fuel pump can develop a fault that can cause the wiring connections in the loom to the pump to overheat and melt slightly.

If you remove the spare wheel etc, you will expose the tank and you will be able to see the loom going to the fuel pump module that sits at the top of the tank, in the center. Follow the loom away from the tank, and you will shortly come across another connector. Separate and examine. Ideally you should remove the fuel tank, extract the module, and inspect the connections inside the tank, as these can melt too!

Tank removal is quite easy except that ramp access is really required to separate the fuel lines from the tank. The items you mention on your car are common-place on XJ4Os.


Clean Sweep XJS

My XJ12 is a 1986 mode and I recently fitted a new wiper assembly from a later car with heated screen washer nozzles. Now while the wipers work on slow or fast speed, they do not work on intermittent or "flick" wipe.

Steve Hodgson

Dave's Response: The wiper assemblies on these XJSs are notoriously prone to problems, and sorting out the correct motor for the year of the car is not always easy. Unfortunately, I cannot give you the part numbers of the relevant parts, as these largely depend upon VIN codes.

Also, a lot of these parts are now no longer available from Jaguar. My best advice would be to find a reconditioned item that matches your year of car, and to fit this.


Diff s/Arms & Manuals - XJRS

I have been a fitter in the motor trade and currently own a Series 3 XJ and XJRS 6.0-litre, for the former I have the workshop manual. First, is there a known manual for the XJRS? Second, is it an easy job to change the radius arm bushes on the XJRS and can I use the same manual from the Series 3 to help me carry out the work? Third, does the same apply to the diff pinion seal which I need to replace on the XJRS?

John Somers

Dave's Response: Fitting of the radius arm bushes is the same on all the IRS equipped Jaguars so you shouldn't have a problem working from your XJ6 manual. On the XJRS it is best to turn the bush through 90 degrees, so that the line through the two holes in the bush runs at right angles to the length of the car as opposed to parallel as is normally the case. To change the diff pinion seal is the same whether manual or auto, but you must be careful when reassembling not to add any more preload to the bearings by compressing the collapsible spacer any further.

In order not to do this, ensure that you mark exactly the position of the pinion nut. I do not know where you can get an XJRS workshop manual, I do not have one, but most of the car is essentially standard XJS.

If the car is equipped with the Zytec engine management system then unfortunately. like the rest of us, you will have to work out any problems from scratch!! I hope this answers your queries, but unfortunately. technical information on these cars is very thin on the ground.


Obscure Running Problems

George Bath seeks advice on obscure running problems on his XJ4O 2.9-litre. It is a 1990 car with a recorded mileage of 86,000. He bought the car in 1994 with a full service history. Used from April to October each year and then garaged for the winter, in 1995 he noticed a tendency for revs to wander during warm up and also to stall if starting rapidly from rest. His local dealer replaced the idle speed control which didn't seem to make a lot of difference and the injection ECU because that's what showed up on their diagnostic machine. This did appear to cure the tendency to stall when doing a rapid start.

This year the wandering has returned, although not consistently and sometimes the car will not pull away (no power). Also randomly on a run the car will go sluggish and the fuel consumption will rise. More recent investigation by the dealers showed no fault codes, but they cleaned the throttle butterfly and did an engine set up. All was well for about one day. The only other clue is, at the recent MoT the CO reading was low at 0.5. The dealer had previously set it up to 1.0 and then set it to 1.7.

Dave's Response: The 2.9-litre engine has a throttle switch enclosed within its casing. It is common in these engines for oil to pool in the base of the throttle body and this will find its way down the throttle rod into the switch itself. This can then present problems with contact. This area is certainly worth looking at.

As a matter of course the valve timing should be checked.


Bulb Failure

Robin Cameron recently purchased a 1993 3.2-litre XJ4O S with 80,000 miles on the clock and it has been suffering from certain lighting bulbs going out but without the usual "bulb failure" warning. The rear left tail-light wasn't working, nor the adjacent left number plate lamp. All other lights worked but no bulb failure warning and on checking the bulbs were in good order.

Under dealer warranty a new bulb relay and failure module was ordered, but when this was installed the lights still didn't come on. He rigged up a cross feed from the offside to an independent bulb dangling in the tail lamp lens cavity to keep the car legal but still no news of the actual problem. I have now also found that at night only the left hand of the four rocker switches on the centre radio/heater array lights up. The rear window heater rocker glows properly but the central locking and map light switches remain in darkness though they all operate their functions correctly.

Dave's Response: Problems like this are very difficult to diagnose by mail but I think the problem is most definitely not the bulb failure module. It must simply be a break in a wire or in one of the multi pin connectors. A signal is sent from the headlamp switch to the nearside bulb failure module. If no signals are being sent to these particular lights by the module then the lights will not illuminate. Unfortunately between the last multi pin connector, just short of the bulb failure module and the headlamp switch there are three to check and of course, the problem could be in any one of them.


New shocks

John Maltravers is about to change the shock absorbers on his 1987 XJS and wants to know if it is best to use the original equipment or change for something else better, perhaps from the Jaguar parts bin of other models.

Dave's Response: I always recommend the fitting of genuine Jaguar shock absorbers as they give the best "together" feel to the car. The choice is yours, but as your car probably falls short of the date when the rear anti roll bar was fitted and you want a harder, more resilient suspension go for the sports spec" shock absorbers. If alternatively you want a softer ride go for the standard type for your model.


Smell of Petrol

Mike Daffin has an annoying problem with his 1985 XJ6 Series 3 saloon.A smell of petrol when the vehicle is moving with either the sunroof or any windows open and it makes no difference if the vehicle is running hot or cold. He has looked for the obvious leaking pipe hose joints and can't find anything.

Dave's Response: On the assumption you have checked all the usual areas as indicated plus checking, of course, that the fuel tank(s) are not leaking from underneath, it is possible that a vent pipe has come adrift from the car. The only way to check this is to physically remove the tanks from the car. That way you cannot only just check that the vent pipes are affixed and in good condition but also that any blanking plugs put in by the factory originally have not come out or are loose.


Fitting a pre-cat exhaust system

Another XJ4O (4.0-litre) query from John Dean. After damaging his exhaust system (including catalyst) in a car park is it possible to now fit an earlier exhaust system from a 3.6-litre pre-cat model? Considerably cheaper than his own system and he thinks it will fit, but will it pass the next MoT without a cat fitted?

Dave's Response: Yes the older system will fit and yes it is cheaper, but you will have major problems with the control systems on the car. Changes in the electronic sensing would make it prohibitively expensive to do this. Perhaps a better solution would be to purchase a centre (catalyst) section from another 4.0-litre car secondhand. The catalysts are very long lived unlike many modern smaller cars.


Brake Warning Lights

Member with a 1991 4.0-litre XJ4O. The brake warning light keeps illuminating, fluid level, pads, operation of brakes and the ABS light are all OK. Initially the light would flicker a couple of times during normal driving and now this has progressed to the point where it is now almost permanently on.

Dave's Response: By brake light, we assume you mean the light depicting the (!). This is indeed a warning light, but also on XJ4Os warns of brake pad wear. It is also a warning for low brake pressure as generated by the ABS brake pressure pump. On the 4.0-litre models it's not uncommon for the low pressure signaling switch to fail. The reason why the light is coming on is almost certainly because the contacts on that switch have failed. The fact that the brakes are apparently working correctly, in this respect doesn't mean you have to have system pressure. If you listen to the engine on cold start in the morning you should hear the ABS pump build up pressure. As such, the current situation is probably of no consequence at this point to driver safety. However, it is important to replace the switch as the warning light is there for a reason.


Locked Out - no VCM

A member left his 3.6-litre XJ4O running for a while, and when he came back he found he'd been locked out (with the keys in the ignition), the headlamp washers working and the on-board computer playing up and no readings on the auxiliary gauges. Spare keys got him into the car but still no response from the other electrical areas.

Dave's Response: This is a very difficult to answer without actually seeing the car. The problem sounds as if it had been instigated by a voltage fault as a result of some form of battery drain. I would therefore suspect that the problem lies with the central processing unit located under the left hand side of the dashboard (right hand drive cars). However, as this can be expensive it's worth getting the car properly checked before going any further or at least telephone me direct to ascertain other connections, eg alarm and immobiliser systems that could have caused the problem.


No Air Flow

There appears to be very little air flow on the air conditioning system of an XJ4O. Both blower motors are working, there appears to be no blockages when the cowling in front of the windscreen was removed and upon checking the vacuum lines, they too seem OK. The owner has found a red pipe behind the battery, which led to a valve on the heater pipe and when sucking the pipe it appeared corroded so was replaced.

Dave's Response: It is difficult to imagine where the problem lies without looking directly at the car. If both blower motors are working and there was no vacuum in the system, you should still get air coming out of the lower vents, which are fixed orifices and not varied by vacuum control. The only logical explanation at this point would be that one of the blower fans has been removed in the past and replaced without making the necessary connection to the centre air distribution box. In such a case, the fan will blow air directly into the car and so volume and velocity of air will be lost.


Dim-Dip System Failure

Sometimes one light will work on dimmed, sometimes the other, sometimes both or none will work. A cursory glance at the circuit boards shows nothing and the owner would now like to disable the system if possible.

Dave's Response: The circuit boards are more than likely the problem, and if you examine them very carefully you will probably find dry joints on both of them where the multi-pin connectors clip together. Get the boards out very carefully look at the array of multi-connectors. I would recommend re-soldering them anyway. It's not possible to disable the system as it forms an integral part of the cars electronics.


Aftermarket Alloys

Member has lattice style wheels fitted but not standard Jaguar type, identified under the name of Miglia. One is now damaged and he needs a replacement.

Dave's Response: Can't help with aftermarket wheels. Try all the regular suppliers in your area or advertise in Jaguar Enthusiast for a replacement.


Alarm Contact

A members car is fitted with an all-singing. all-dancing alarm system, but with only one key and one over-ride key. He wants to get more but can't contact the original supplier of the equipment. Halfords who retailed the system will get the parts but at a cost!

Dave's Response: Aftermarket alarm systems need to be approached carefully and if you have any problems or need parts like new keys I can only suggest you grit your teeth and contact Halfords. You can understand, for security reasons, that an alarm company may not want individuals to contact them directly.


Pressure Fuel Cap

A member's concerned about the amount of pressure released when he removes the filler cap. Is this a problem?

Dave's Response: No, this is normal on XJ4O models.


ABS Warning

Warning light comes on but extinguishes after starting the engine, but after about 10 to 15 miles, and always on a right hand turn, the ABS failure light come on again. Can the sensors be changed over to aid diagnosis or are they specific to a particular wheel?

Dave's Response: Yes the problem is almost certainly one of the ABS sensors, and whilst in theory you can change them over, in practice you will probably damage them when you try to extract them. So you should therefore get an ohmmeter, connecting one terminal to the earth of the car and the other in turn to each terminal of the sensor side of the multi-pin plug in the boot. If there is any continuity to the earth at all, the sensor will be at fault. The only remedy is to change it.


Radio Operation

Can't programme radio/cassette unit for memory radio stations.

Dave's Response: This depends on the unit you have fitted, but in the majority of cases all you have to do is manually turn into the correct station you want. Then press one of the station pre-set buttons and hold it in until you get a bleep. This confirms the station is memorised and by pressing the same button at any other time will automatically retune the radio to that chosen station.


Air Con in a Flap

This owner is only getting hot air to the face and windscreen vents while the full range of temperature can be achieved to the footwells.

Dave's Response: This will be caused by a seized flap control motor. The flaps to control temperature at face level are separately controlled to the footwells. The top flap motor on the side of the air distribution box can only be accessed by removing the instrument pack from the dashboard, which in itself involves removing the dash liner and the four screws that secure the 'pack' in position. Ensuring that the battery is disconnected, you should then release the multi-pin connectors at the back of the instrument pack so that it can be removed completely from the car. Identifying the flap motor and using Tippex to mark the casing of the box at the axle where it just pops through gives you a reference point to identify how far the axle will move when you turn the temperature control on the dashboard. To do this, however, you need to reconnect the battery, being very careful to ensure there are no loose wires or multi-pin connectors that could earth on anything before you do it.

If, when you turn the temperature select control, the axle does not rotate, gently tap the motor to see if it then starts to turn. This may rectify the problem, but if it doesn't then you will have to remove the flap motor. This should be done by removing the entire dashboard assembly, although it can be done in situ with great care and the use of small screwdrivers.


Low Brake Pressure

This warning light appears on the display screen, which took longer and longer to extinguish over a few months until it is now on permanently. The owner has not noticed any deterioration in braking efficiency. The workshop manual indicates that the accumulator and two switches are changed. Is it worth purchasing a secondhand accumulator sphere (as new ones are around £100) or is it something else?

Dave's Response: It is correct that the problem's more than likely the nitrogen accumulator sphere. This works on the principle that on one side of a diaphragm there is gas and on the other side fluid is pumped into it hydraulically. As the sphere fills up. the nitrogen is compressed which provides the reserve pressure in the system. Over time these diaphragms can relax or even perforate. I do not recommend using a secondhand unit.


Dead Circuits

The bonnet lights don't work because there appears to be no earth. The nearside dip-dim when switched on momentarily lights on dip but will not light on dim. Nearside indicator sometimes gives lamp failure warning.

Dave's Response: Bonnet lights not working is normally caused by corrosion to the bonnet light switch. If you disconnect and short out the terminals to the switch, this will prove continuity or failing that replace the switch anyway. The dim-dip problem is usually the failure of the unit, but most people try to replace it with a secondhand one, which may in itself not be good. These suffer from dry joints on the circuit boards. So it's best to replace it with a new one. As both front units are the same, it is possible to exchange them, so if you do this and the fault moves to the other side of the car, then you do have a faulty unit. If this doesn't happen you could have a wiring failure somewhere between the bulb failure unit and the lighting switch.

The indicator trouble could also be a bulb failure unit or the earth. Re-check the earthing connection as this is most likely to be the problem.


Leaking Roof

This time a Daimler XJ4O with a leaking sunroof which is causing water to run down the driver's side A post.

Dave's Response: Water leaks from the XJ4O sunroof s are not common as they are usually sealed very well, but the drain tubes can get blocked. In the first instance, retract the roof electrically and with an extended coat hanger, welding wire or other thin wire and then try and feel for the drain hole where it comes down from the top corner. Failing that, if you go to the driver's side wheelarch, you can identify one or two pipes emitting from this area closing panel. One of these is from the sunroof area and if you blow back with compressed air or foot pump this may clear the blockage by back-flushing. However, I would suggest you cover the upholstery as a protection in case a fair degree of dirt is dislodged. Furthermore, if you want to remove the sunroof assembly from the car for further inspection, this is quite easy as the entire electrical assembly is bolted to the underside of the sunroof panel so it all comes away as one. However this does involve removing the headlining, which is messy if not complicated, so it's advisable to read the appropriate workshop manual before carrying out the work.


Cruise Control Non-Operation

The cruise control just does not work on a 1988 Daimler Double Six XJ and hasn't worked since the owner bought the car. The two amp fuse located in the fusebox under the right hand scuttle continually blows.

Dave's Response: If the fuse is continually blowing it is probable that there is a fault in the on/off swjtch, select switch, control, wiring or the actuator itself. If the two plugs to the actuator unit are disconnected (situated underneath the engine behind the air conditioning compressor) and you fit a new fuse, then drive the car down the road engaging the cruise control. If the fuse doesn't blow then the actuator is at fault. If the fuse does blow then you have to work back from there. Start by checking if the fuse blows just by turning the cruise control on or does it blow when you select the desired speed on the stalk. This will at least indicate the part that is perhaps giving the trouble.

There is a diagnostic procedure and equipment to check the system out fully and you would either have to find someone in your area who can carry this out for you or you could contact me further by phone for more help.


Kangaroo XJS

A 1986 XJS 3.6-litre with manual gearbox has a recurring fault. Whilst changing down the gears, the car experiences a 'kangaroo' effect on deceleration. The car does start first time every time, hot or cold, and there is no apparent misfiring. At the last MoT, only a few weeks before, there were no emissions problems, the correct type of Champion spark plugs were fitted, the distributor cap and rotor arm were replaced and so were the coolant and air temperature sensors. The owner has also checked the rear driveshaft, UJs, propshaft, flange nuts and engine mountings.

Dave's Response: The 'kangarooing' is probably due to a combination of circumstances. The first is valve timing, which is prone to going out of sync on these AJ6 engines as stretch appears in the timing chains. The best thing to do is to remove the cam cover, accurately ascertain TDC of No 1 piston and ensure that the notches on the camshafts are correctly aligned to the camshaft setting tool. With this checked and adjusted if necessary, the next area to check is the throttle potentiometer. This is a variable resistor with an end stop which is located underneath the throttle housing above the oil filter. This sends a signal to the ECU, giving an indication of acceleration and deceleration and also when the throttle is open or closed. This can be likened to a radio volume control knob and, as I am sure you may have experienced, given time, when you turn the radio up or down there is a crackling sound generated by wear in the track.

On your switch this 'crackling' is being transmitted back to the ECU which may be causing the erratic effect as the ECU is effectively switching on and off the fuel injectors to match the crackle.


Sucking Filler Cap

Member complains that when he removes the fuel filler cap on his XJS AJ6 engined car, there is a loud sucking noise and wonders if this could be one of the three vent pipes blocked.

Dave's Response: Petrol tanks and the filling thereof has been a thorny subject on XJSs since day one. Over time certain groups of cars have been the subject of recalls by Jaguar dealers for modification to improve tank venting. In the first instance I would contact your local dealer, quoting your VIN Number to determine if your car was amongst those that should have been recalled, and if so, whether it's been subsequently modified. If your car should have and has been modified, then a stage further would be to look at the three vent pipes taking them all off to establish if there are any blockages. At the rear of the car one vent pipe emits just forward of the rear nearside wheel above where the left hand handbrake will come out from the chassis.


XJS No Cooling Fan

Owner of an E-reg XJS finds that the electric cooling fan doesn't operate when the air conditioning is switched on.

Dave's Response: This member has tried several ways to identify where the problems lies unsuccessfully. What I tend to do is link a feed to the fan via another relay switched by the direct control to the air conditioning compressor. The current draw to switch the low tension side of a simple 4-pin relay is still sufficiently within the limit not to blow the 10amp feed fuse. We then take a live supply from a suitable source like a headlamp in order to drive the fan. It is important to use a correct resistor relay in order not to over-strain the system. However these cars are adequately fused, so if you do make a mistake the fuse should take care of it.


All Buzzers and Lights

Member with a 1990 XJS can't get his seat belt warning light to illuminate, nor is a buzzer working which the workshop manual tells him should!

Dave's Response: Much of the seat belt light and buzzer logic systems were only fitted to certain export market models so the workshop manual is probably referring to these. The only seat belt warning system that should be fitted to your car is the warning light in the instrument panel whereby when the driver sits on his seat, the light will illuminate until the belt is fastened. Similarly with the front passenger seat. The fault here therefore is probably simply where the seat belt plugs into the receptor at the side of the seat or a disconnected wire underneath the seat.

Regarding a 'buzzer', the only audible warning to UK spec cars was a 'chime' warning the driver when lights were left on when a door was opened. There is no warning on UK spec XJSs when the ignition key is inserted or removed from the lock


V12 Rattle

An XJS V12 has a rattle from the forward end of the engine. The noise manifests itself on tickover and if the engine is revved the noise disappears - the rpm settles and the noise returns.

Dave's Response: The problem will be caused by wear in the timing chain and tensioner, the rattle being the chain catching the housing. This noise will occur when the engine is on a very light load. The work is extensive and very time consuming, but can be done by a DIY mechanic with care. It can also be done in situ without removing the entire engine, given that you are exceptionally careful to remove the timing chain case without removing the cylinder heads or sump. However, replacing the case afterwards without snagging the head gaskets is extremely difficult, so it is best advised to remove the sump. This work, including the work on the timing chains would, for an experienced V12 mechanic, take up to 20 hours to complete.


XJS Leaking Windscreen

After some damage, this XJS had its windscreen replaced, since when the car has continually suffered from water leaks into both footwells. Despite a new windscreen rubber, the leaks are still there.

Dave's Response: It sounds very much that, if the leaks were not there before, either the windscreen fitters have not used the correct sealant or more likely that they have inadvertently blocked (with excess sealant) the drainage ports that are underneath the A post chrome trims. This allows water from the rain gutters to escape. If excess water is building up in that area it is not impossible for the water to eventually find its way through the screen. Alternatively, the only other item to check is the windscreen seal itself. Evaluating this from the inside would mean removing the dashboard casing and A post internal trims. Then soaking the car from the exterior with water should reveal where the water is gaining ingress.


Blocked Drains

My 1989 XJS 3.6-litre has developed a water leak into the front footwells. This only occurs when the air conditioning has been running.

Dave's Response: A common problems with XJSs and Series XJs caused by blocked drain tubes. By removing the centre console side cheeks you can see the nylon plastic pipes that run vertically which are the drains from the air con system to the atmosphere. These normally allow the water to drip down underneath the car and out onto the road. These drains get blocked from road debris and need cleaning out. The pipes easily pull free, but beware when cleaning out be prepared for a possible deluge of water which will undoubtedly leak onto the carpets. so it is not a bad idea to remove all the carpets and underlay first before doing this job.

As the leak has probably been occurring for some time, it's advisable to remove all the carpets and thoroughly dry them and the floor area before putting them back, as mildew will develop and possibly cause corrosion of the floorpan in time if left as is.


Double Six Wiring

For my 1989 Daimler Double Six saloon, my local Jaguar dealers inform me that a replacement injector harness is needed on my car as the existing one is now brittle. Although I authorised them to do the work, they advised me that Jaguar could not supply one. Although a replacement was acquired from an outside supplier (SNG Barrett). when it arrived it did not fit and there are amendments that are needed in order for it to work. There does not appear to be any wiring diagrams to use so has this problem occurred before?

Dave's Response: Jaguar can no longer supply this item and it is only available from Barretts. although it must be remembered that the spec of the models changed many times over the production period so it's not possible to provide a myriad of wiring to suit every model. They're relatively easy to adapt and in fact Jaguar do produce some repair kits' for existing looms.


Info On Forties

Having recently acquired a 1990 Jaguar Sovereign with automatic gearbox, the car doesn't appear to be equipped with a power hydraulics system, as there's no pump attached to the timing cover, and the brake servo is an electric pump mounted below the master cylinder. Even so the reservoir for the power steering has a label on top of it which states 'Caution Power System Hydraulics'. Can I use Dexron 2 in the steering system? Secondly, the car is designated 'Sport' as it has a smaller steering wheel with a sport logo on it and also a 'Sport' icon appears on the instrument panel when the ignition is turned on. This however disappears on start up and doesn't appear again. Is this 'Sport' icon and steering wheel just for show, or. if not, what does it mean? Lastly. could I have some data about the engine power output as I intend to tow a caravan with the car and would like to compare it with my previous vehicle.

Dave's Response: On these later cars the braking system was supplied by Teves and uses electronic pressure pumps. The only cars of this style which were fitted with hydraulic pumps were the ones which had self-levelling suspension which this car doesn't have. However. the reservoir for the power steering does still need to take HS fluid anyway because this is what the system is designed for. You cannot therefore use Dexron 2 in this car. On the matter of the 'Sport' designation it does have a meaning, although the steering wheel doesn't sound like the original type supplied with your model. You will find a Sport switch on the J-gate gearlever surround, which, when activated, will show the 'Sport' icon in the dashboard illuminated. With this selected, gearshift changes will be altered to suit more spirited driving techniques. It would appear that the owner either doesn't have a handbook or is referring to a handbook from an early 3.6-litre model of the XJ4O. It's a simple matter to acquire the correct style of log book either through a Jaguar dealership or from the Club's Regalia Department. This will also provide all the technical data on the engine required.



Two problems with my XJ4O and together they compound one another. The engine will not idle evenly; at times it will either surge between 700 to 1,500 rpm or cut out altogether. When the engine cuts out it will start straight away but will not run. After about three starts the engine will rev to 1,500 to 2,000rpm without me touching the accelerator. I have to wait about 20 to 30 seconds for the revs to settle before I can engage the drive. Secondly, the problem is made worse because of the engine cutting out. The car can only be started in PARK instead of park or neutral. This makes it awkward in traffic when the engine stalls and you have to physically stop the vehicle and put into park.

Dave's Response: The idling and cut out problem is probably due to a combination of factors. The first is probably incorrect valve timing as 3.6-litre engines are prone to this. Before anything else therefore you should establish the correct TDC position followed by checking, and if necessary rectifying, the valve timing. You can look at the possibility that the stepper motor on the idle speed control unit but also the air bleed by-pass within that unit as well. There is a lot to look at here so it's probably best to make personal contact over the phone to review the options in more detail from which we can ascertain all the information and perhaps make mention in a future issue of the magazine.


Height Challenged

Having recently purchased a 2.9-litre XJ4O saloon I found the drivers seat too low and particularly so for the wife, a mere 5ft 1in, so she is unable to drive the car as it is. Is it possible to raise the seat in any way with a conversion?

Dave's Response: There are two choices here: it would be possible, but not necessarily advisable, to fit spacers and longer bolts to the seat rails to effectively raise the level from the floor. I say inadvisable because the bolts would be under more stress and in the event of an accident could shear. The more practical solution would be to change your seats for the electrically controlled type from the upmarket XJ4O models. These are adjustable for height. To acquire a set wouldn't be difficult as so many of the older or damaged cars have gone to scrapyards who are stripping them for their valuable spares. All the wiring for these seats is already in place in the 2.9. although you'll need a new centre console which incorporates the electric switchgear as well.


Clickety Click

The central locking on the driver's side of my 3.2-litre XJ6 has began to click before engaging closed. Opening the lock was and still is no problem. The clicking noise is not as pronounced now but the lock now will not open. I have to access the car via the passenger lock which works perfectly.

Dave's Response: To clarify this problem, is it that you cannot operate the lock with the key or that once you use the key you cannot then open the door again? If it's the former then it's a mechanical problem with the door lock or the key. If you have another key to try or if you get another key cut, this could solve the problem. Before that however try spraying some WD4O into the door lock mechanism and see if that helps. If it's the latter, then it must be a mechanical problem at the back of the door handle assembly and/or the micro-switches that govern the overall central locking mechanisms. This would mean stripping down the inside of the door to determine further what needs doing.