V8 Spark plug change. S-type specific. XK8,X308,X350 also

[J44EAG]

A few slight low speed ignition misfires lead to this plug change on my MY02 4 litre V8.

Iridium plugs were 23k miles old and upon removal original plug gap of 0.9mm had increased by 12.5% to just over 1mm. Quite a fast wear rate which when worked out across 8 plugs gives an air gap overall increase across the engine of 0.8mm. That doesn`t sound much until you relate it to the original single plug gap of 0.8mm. The wear amounts to the equivalent of the total original gap of ONE spark plug. That is getting on for unacceptable from increased fuel consumption reasons if not anything else.

Misfiring plugs lead to coil failures. Dave Marks will tell you the same. Coils do not respond well to tired or broken down plugs. At around £35 each for a coil replacement, it makes financial sense to change plugs at the earliest opportunity if misfires occur. I keep a rigid record of service mileages for oil and plug changes. In doing so I hope to keep necessary expense to the minimum.

The work described below is also applicable to later 4.2 V8 units generally and also V6 models which have some similarities.

The 4 litre engine is certainly crammed into an S-type. There is hardly space to operate a 1/4" ratchet above and around the back of the engine adjacent to the bulk head. I get the impression that the car was designed primarily to accommodate the physically smaller V6 as a design concept. The V8 is literally shoe horned into the chassis.

The offside cylinder bank is reasonably easy to work on. Those cylinders are stagger mounted forward relatively to those on the opposite side of the car ie closer to the radiator.

To change the off side plugs, remove the air cleaner box top complete with airflow meter and MAF sensor having slacked the jubilee clip from the throttle body trunking. The two crank case breather connections need to be removed from the trunking also. The whole assembly can then be lifted from the car.

Using a 7mm socket on a 1/4" ratchet with short extension bar, release six 7mm bolts holding the spark pug cover to the cam cover. The cover will lift away revealing the plug on coils. Release the connectors from the coils, remove the 7mm bolt on each coil pack and simply pull the coils from the spark plugs below. Remove old spark plugs and install new with a trace of copper grease on the threads. Reinstall the coil packs and their bolts. Refit the electrical connectors and refit the spark plug cover. That`s the job done on the off side. Nothing difficult about it. Time taken about 40 minutes.

The nearside spark plug bank is identical to the offside, so the above applies. However, on an S-type this is where it can become exceptionally difficult due to lack of space. In addition to the above guide, remove the fuel purge unit nutted to two of the top suspension studs on the top of the turret. Now try to get a 7mm socket on the lower rear spark plug cover bolt then fit a T bar or small flat 1/4" ratchet to the socket. Almost impossible due to the top of the engine being so close to the engine bulkhead. So what now?

I cut 4mm off both ends of a 7mm socket. Not easy in a yard with just mole grips and a hacksaw. Proper "in the field" get you out of trouble so called engineering. I was then just able to get socket and ratchet on the bolt head. Eventually, I cut through an obstructive and completely functionless end off a cable support bracket with a hacksaw to gain space. Still unable to operate I removed the bracket from the inside face of the near side suspension turret to which a flexi fuel line is fixed. That gave the hand and arm space I required to tackle the completely obstructed bolt head. But only just...this is a pig of a job.

Once loose, the bolt can be backed out with fingers and the job can proceed as detailed above. However, note that the rearmost spark plug can be difficult to remove as again there is little height to enable a plug held in a socket to be removed with an extension drive bar in place. The secret is to separate the extension bar from the socket after the plug is free of the head and recover the socket and plug from the spark plug well using an appropriately sized Allen key as a fishing rod! A magnet on a stick might also be useful. Fitting of that rear plug also needs the above treatment to recover the plug socket once the plug is tight.

I made sure all coil and cover bolts ran well before assembly and cut a slot (instead of the bolt hole) on the spark plug cover rearmost bolt hole. That meant the rear lower bolt could be run in to a little over cover moulding height and tightened only the last few turns instead of having to madly ratchet the complete bolt length. Having fitted the spark plug cover and all other dismantled parts the job is done. Note that due to the difficulties extracting that lower rear bolt, the plug change on the nearside bank took some three hours compared to the forty five minutes of the offside bank. This left me with abraded, scuffed and ragged hands. The nearside plug change on the S-type is not nice or funny but it has to be done occasionally.

I seem to remember the guy who used to look after J44 groaning hugely when I took the car in for a plug change. Now I know why. I wouldn`t want to be doing that job everyday of the week. Now when you get a huge bill for hours spent V8 plug changing you know the reason why!!

So that is the latest tale from the riverbank. I hope it is useful.

Mike

Late edit. Having driven the car for a few miles today, slow speed pick up from standstill is sharper and the accelerator feels "lighter" with the engine being a tad more responsive and free running. That should save little on fuel and perhaps give slightly lower emissions at MOT time in a month or so. In my opinion the work was worth the effort in keeping the engine in tip top condition.

Second edit for images applicable.

[richardtoulouse]

Mike,
thanks for your explanation, I plan to change my sparks (even if the car made only 50 000kms ie 31 000 miles) in the next days.
However, in the specification you provided, the reference of the part is AJ8 4575 (iridium).
What parts are the commercial parts references?
What is the manufacturer? NGK?

Thanks for your advice.

[J44EAG]

Hello Richard,

The part number I gave was for AC Delco spark plugs specific for the 4 litre V8 S-type was R5606. The AJ8 4575 is probably a Jaguar supply part number.

Since writing my article in the magazine and also telling the story here on this post thread, I have to report that the fitment of the AC spark plugs has caused problems.

When the car is driven carefully in a town or city location, the engine runs well. HOWEVER, when the car is driven on faster roads or on the motorway, problems become evident. On steep hills, at small throttle openings and when under load, the AC spark plugs appear to break down and misfire badly. That is accompanied by a severe loss of power. I then have to kick the car down into a lower gear to keep engine revolutions higher and "drive through" the misfire region of the rev band. That is frustrating and wasteful of fuel. The fitment of the AC plugs has not gone well.

I now need to remove the triple electrode AC plugs from the engine as I feel they are not suitable, despite being listed as correct for the car. I have therefore decided go back to NGK IR plugs under the part number of IFR5N 10. I am confident that fitting such plugs again will cure the issue that I now have.

I hope that is of help, Richard.

Mike

[richardtoulouse]

Dear All,
my knowledge on the S-Type is increasing. This morning, I propose to share about the spark plug.

Main of the parts in my car has been fiited by Jaguar when it was manufactured. Because I was adviced about the tensioner, I am going to refresh many parts, incuding the sparks.

Mike experience with "seconde source" spark reinforced my desire to replace the parts with the original reference.

They are NKG PFR5G11 E

I received from my suplier PFR5G11. As a scientist, even if the vendor ensure me that they are the sdame, I had a call with NGK technical department.

They confirmed that they are not the same components.

The difference is on the resistor of the item. 5K Ohms instead of 10K.

This value is very importante for two effects. The first one is related to the voltage deployed in the combustion chamber, the second one is teh effect on the electronic ingniter.

Because we have no information on the design margin of the ingniter, I strongly recomend to operate the igniter with the recomanded load.
When I said that we have no knowledge of the igniter, it is not correct because they are knowned as to not have a very hight level of reliability......

So, personally, I requested from my vendor to supply with me the NGK PFR 5 G 11 E

Hope it will help people; liek me, try to found the correct item.

[J44EAG]

Hello Richard.

Thank you for that information.

I have learned something this morning from you.

The plugs that I previously had fitted to my 4 litre 02 V8 were NGK IFR5N10 units. These worked well in general service.

What you say is good. This might explain why I am having issues with the triple electrode AC Delco plugs that I recently fitted. Perhaps they are of an incorrect value, even though they are listed for my car.

I think you have made a wise decision to fit new original specification spark plugs.

Perhaps fitting after market equivalent plugs is not such a good idea. Clearly variances occur when equivalent of copies of the original items come onto the market.

Mike

[J44EAG]

An update on what I saw as a spark plug issue following installation of a set of new AC Delco spark plugs in my V8. Mis fires occurred under load, up hill on the motorway and on dual carriageways. Typically I`ve seen this before on both V6 and V8 cars that I`ve owned. The misfiring would tend to occur at 1600 and 2300rpm. On one occasion, changing the plugs cured the problem.

You will see from a couple of my later posts above, that I suspected that I may have installed a set of plugs which I felt may not be wholly suited to the car. I now appear to have been incorrect in my assumption.

Following a couple of bad misfires last weekend which caused the engine check light (MIL) to illuminate, I`ve just got onto the job. I was about to tear out what I considered a bad set of plugs from the engine, re-gap the old ones and see where things went from there.

Before firing into the job, I noticed that the throttle body cable plug was not fully home in the body socket. This despite a cable tie used to ensure that it didn`t move. Regretfully, the security clip which secures the plug to the throttle body was broken before I took ownership of the car. I`d used a cable tie as security but on the last maintenance session perhaps had not pulled it up tight enough.

Having now tensioned the cable tie more fully, the misfires have gone completely and the car is back to normal.

So just a heads up on this aspect of ignition and throttle control then. Good contact between plug and socket on the throttle is essential. The symptoms for bad plug and socket contact are identical to that of worn spark plugs so it is always worth looking at this throttle area before changing spark plugs or coils which may still have plenty of life left in them.

I`ve learned something this morning then.

I have still to extinguish the MIL lamp on the dash. This illumination is a tell tale to the driver that a significant electronic "event" has occurred which needs investigation. Driving with the MIL lamp lit will not cause any damage. It is purely a signal to flag up that a problem has occurred.

The MIL lamp can be extinguished by disconnection of the negative battery lead for twenty minutes. This is known as a "hard dump" and clears the computer memory of any residual fault codes. It is effectively that same dumping situation as would occur if an electronic interrogation unit were to be used on the car. An interrogation unit does have the advantage of avoiding battery disconnection.

If you do chose to "hard dump" your modern Jaguar using the negative battery lead disconnection method, thus avoiding garage charges, note that you will need to reset the clock and re-programme the radio code. Best to ensure you have the radio code to hand before you commence such work.

Nice to loose the coughs and splutters. It makes the car far more pleasurable to drive without misfires which have to be driven through often by kicking the car down a gear.

Mike

[Occulomency]

Mike,

Would you recommend these plugs for my 07 plate STR?

Cheers,

Fraser.

[J44EAG]

I`m in two minds, Frazer, as to whether triple electrode plugs really have many, if any, true advantages over standard plugs.

There has been some criticism that having so much extra electrode area upon the plug end, that it might cause an unacceptable degree of flame front shielding during the combustion/power stroke. Conversely, triple electrode plugs have been known to be good at keeping plug fouling to a minimum and provide smoother running for the first few minutes after start up.

That having been said, now that I`ve solved a poor connection issue on the throttle body, misfires have gone and I now consider that these triple electrode plugs are certainly suitable and correct for my non supercharged V8.

It is difficult to compare normal or triple electrode plugs for running differences unless we have two identical cars side by side and fitted with the different plug types. Even then, I would suspect that differences would be hard to quantify. What I can say is that I noticed better running at idle on the new triple set when compared with a 23k mile old set of standard Jaguar plugs that I had just removed. Pick up from stand still was also improved.

Triple electrode technology is not a new idea. Similar plugs from several manufacturers have been around for many a long year. Provided that you chose an exact cross reference for the plugs fitted in your car, I see no reason why fitment should cause any issues. I would however be particularly careful to buy well known main stream brands rather than makes with unknown manufacturing heritage.

The only true test of any product is in the operation of that unit in service. Sometimes things go well. Other times disappointment can result. Given the correctly selected plugs for your car, I don`t think you can go far wrong fitting plugs similar to the ones I installed. I`ve no issues with them now.

Mike

[J44EAG]

Further to my earlier post, I`ve just tripped over these Denso TT (look like standard type twin tip) spark plugs on eBay.

Whilst not the triple tip items I discussed above, they are offered at a very reasonable price and are suitable for all years of S-type R.

http://www.ebay.co.uk/itm/JAGUAR-S-TYPE ... 5d33458b31

Plugs vary in price wildly. The higher the price, generally the longer rated life. Typically plug life can vary from 10k to 100k miles dependent on specification and manufacturing material grade. As a guide V8 type plugs fitted at the factory had a rated lifespan of 60k miles. Later plug life was (and I stand to be corrected) increased to 100k miles.

I think before taking the plunge and buying these plugs, a little research needs to occur to see what the life expectancy is for this particular Denso TT product. I`ve seen some plugs priced at around £10 per unit but they have tended to be the top of the range items. Quite where these items are placed, we need to find out.

For the price, if you are in desperate need for a plug set to keep you going at a budget price, these might just do the job nicely even if they perhaps were only rated at 30k miles.

Mike

[richardtoulouse]

Fraser,
I would like to say that the spark units have to access. the electrically one and electro-chemical one.
I stay convinced that the apparent load seeing by the igniter is very important, from reliability point of view,for the electronic igniters that we have in our cars. I work hard to get the original spark units (see my previous exchange) in order to have the correct electrical load. (I still waiting for them....)

The second aspect (fire function) is more complexe. I had an interesting discussion with NKG technical department that explained me that the flame propagation is also function of the resistor value. We can undesrtand that by the fact that an electronic igniter is a system that store energy and rapidly provide it to the combustion chamber. More the resitor value is, longer will be the time to descharge the energy into the chamber. Therefore the flame duration is function of this resistor. The energy level provided to the chamber is not function of the resistor (even if thay are some loss that are negligeable), is it only dependant of the igniter unit.

Regarding the number of electrode, my knowledge came from "oral propagation". I start to be a specialist in Alfa Romeo and for the marvelous engine ( 1951 - 1990) I will never install others sparks than the original Lodge units with four electrodes. The "old guys", who used the cars in 70's told me that if you do not use the four electrodes, you will have a holl in the piston!
I am not sure it is correct (I assume that the reason is more to not fit the correct level of "temperature code" of the spark units), however, all my Alfa engines are operated with four electrodes....
I don't care of the resistor value because they are not electronic igniter or they are old electronic igniters that are more robust than the current one that we have on our new cars.

In summary, I know that resistor value is very important for the correct behavior of the igniter system; however, for the number of electrode, my knowledge is "cultural". The knowledge of the flame propagation inside this kind of environement is very complex to modelize ( various pression and temperature) and even if I worked on this subjects some years ago to understand the behavior of the combustion inside an engine with gaz, I will never provide any advices about the number of electrodes .....
Regards

[Occulomency]

Thanks for the comprehensive replies.

I am hoping that today's trip to my friendly mechanic will sort my high-rev range miss coughing (he's cleaning throttle bodies and MAF sensors for me).

The next step on the diagnostic trail will be new plugs (I plan to fit new ones anyway).

From then on it's a trip to Jag Tech (I need a full gearbox flush as I've just topped 60,000 anyway), I'll keep you posted.

Again, many thanks.

Fraser.

[J44EAG]

As Richard says, flame front, plug resistor value and combustion dynamics are an extremely complex subject. If any of them are taken outside design perimeters, then problems do occur.

On the basis of that, correct and appropriate installation of suitable spark plugs is vital to an engine. Although it is quite acceptable and very normal to install plugs from alternative manufacturers, installing an identical grade to original specification is essential.

The hand book supplied with the car is the most reliable source of accurate information for ones own car and the plug specification fitted. Over the years, incorrect specification plugs may get fitted by earlier owners and variances may occur which may not be to original or required specification.

Richard has certainly done his research with NGK to ensure he has the correct items fitted to his own car.

It would appear that I also have the correctly listed alternative Delco plugs fitted to J44 although apart from checking an application data sheet, I did not go to the lengths which Richard has done to ensure complete part conformity.

The effects of pre ignition or detonation within an engine combustion chamber can be highly destructive, causing localised "hot spots" which as Richard says can cause the melt down of component parts. The blowing of a hole in a piston is a typical and well known example of the problem. Richard, Brake Buster, dh Dove and myself being or having been involved in the aircraft industry will have been schooled with this issue during our training periods. The issues of destructive detonation particularly at high flight altitudes is therefore familiar .

We are fortunate with the V8 Jaguar range to have anti knock or detonation reduction electronics which to an extent manage the problem of detonation should it begin to occur when we use our cars. Use of the correct grade of fuel is also essential to controlling detonation issues. Use of low octane fuel certainly causes an increased likelihood of detonation occurring. One has to say that standard pump fuels commonly available in Europe and the UK fully meet our needs, but one might have to be a little more careful with fuels sourced in other parts of the world where it might not meet the needs of our V8 or other engines.

A complex subject and thanks to Richard for his post.

Mike

[J44EAG]

Back again on the subject of plugs, coils and misfires.

I`ll add to that, issues with MAF, coolant temperature and air temperature sensors. Failure of any one of these items or several other sensing components can really upset the running of both V6 and V8 power units which are extremely sensor performance critical.

This is a continuing roundabout story with multiple problems having been found in ignition and engine sensor systems. The saga on J44 has become a process of elimination over several months.

All spark plugs were recently changed but intractability issues began to appear almost immediately. Lack of torque climbing hills at light throttle pedal settings, sudden misfires and general engine irritability. New plug failure is rare and I must admit to being slightly lead to believe that the new spark plugs were not performing well. I held back on ripping them all out again as I suspected there were other issues involved. Neither did I want to have to do the job twice with no guarantee that I would be any more successful than previously.

As covered in several of my other posts around the time of this years Weston Park event, J44 became the heap of the show! Not only did the temperature sender fail causing a full overheat condition to be simulated, but when the car was interrogated by Dave Marks, several other problems became apparent.

Firstly the temperature sensor failure indicated the car was overheating when it was not. In turn that upset ecu parameters and fuelling became affected also. So at 77K miles the sensor was dead and had to be changed. Drivability improved as a result of the new sensor and all the warning bells, lights and whistles went out. So far so good, but not good enough.

Dave also itemised a P0113 fault code which indicated a high inlet tract temperature sensed via the ambient air temperature sensor mounted in a rubber grommet immediately upstream of the MAF sensor and the airflow meter in the inlet charge air trunking. I now hope that a replacement ordered will also help a control problem with the internal car cabin heating system and have an effect on the running of the engine. More on that when the part arrives here.

The heating system is currently refusing to fill the car with anything but hot air! The heating is now switched off and the sunroof opened to let the general car heat out into the sky. I`d open the drivers window but the mechanism wires snapped the other day and the door glass is now held up with Gaffa tape and three half clothes pegs as wedges! New mechanism now ordered. Parts supplied by our great friend "Neville the Devil" at North East Jag Spares.

Whilst being interrogated, the car also ran roughly which I put down to the temperature sensor failure. Dave itemised a misfire on the offside bank of the V8, No 1 cylinder. As plugs were relatively new, a coil was suspected. A new one fitted this evening has seemingly eradicated the misfire and the car does accelerate and run much better. I now need to road test and confirm that misfiring has gone when driven on light throttle up a hill before accelerating again without having to boot the car into a lower gear to clear the holding back.

The mass airflow sensor, (MAF) fitted upstream of the airflow meter also appears to have a bearing on misfire potential. Replacement of that item by another member cured his misfires at a stroke. A MAF is around £70 new. I pulled one from a scrap car for £3 and the car instantly ran rather better than previously. Obviously a good second hand part although really only fitted as an experiment. Interesting that the MAF fitted from new to J44 did not show as defective when Dave Marks interrogated the car at 77K miles. Perhaps it was still functioning well enough at the time not to flag up as a problem?

Whilst at Weston, John Cady, owner of a Beecham Mk2/XJR and one of our Portsmouth Region members, also suffered a coil failure and a fuel drenched spark plug on No 1 OSF bank. He managed to find a coil on the Barrett stand but unfortunately no spare spark plug. I had an old one in my ashtray from J44 which together with the coil got him home without further problems. Is this No 1 OSF coil generally an issue on V8 motors or was it just co-incidental that John and I both had coils fail on the same cylinder?

So the pile of time ex failed components continues to grow in my Black Museum, as does hopefully my knowledge on the causes and effects of age, use and life cycle of these sensitive components.

Mike