[modern] spark plugs

Disused Categories Modern
1

Was it in this list that somebody had to have his car’s head off because of
a spark plug electrode deteaching itself from the plug had fallen in the
cilynder.

(It’s only a question, not an affirmation) Would not then the risk of such a
thing happening be multiplied by the number of electrodes?

I need to do maintenance in the Jag (in one month, when I hope I’ll have
more time, and the sparkies will be changed as well I’d like to try these
multi-electrode things if there are no dangers…

Thanks

Lluis

1987 XJ40______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com

2

Hi Lluis,

I had to remove the XJ’s head to inspect for fragmented ceramics from a
spark plug dropping the nose end of the ceramic. This little event was
quantified by the launching of the remaining plug guts into a shallow orbit
in the engine room. I have promised NASA that any more RC9YC launches will
done at the Cape.

The number of ground loops on a spark plug should not be a worry for you.
Events like I described are caused by thermo aging of the plugs and poor
workmanship during cleaning and gapping. Change the plugs every 35 to 40 K
miles and you won’t have a problem. Forget about cleaning and gapping plugs.
Just pitch them in the nearest GI can and get new ones. It will be to your
advantage to use a name brand plug. And no the reason that the plug in my
XJ failed was not heat. The car was a lease car until bought off lease at
the end. Same owner operators…took great care of the care bar none. The
plugs were pulled and cleaned and regapped at 20K miles by a dealer
someplace. It is by popular belief that the tech doing the work bent the
center electrode when extending the ground loop after cleaning. Wrong plug
gapper was used. Probably used an axe to pry up the ground loop to gain a
few thou.
Several of my gear head buddies proved the point to me by duplicating the
conditions on new plugs of the same type. They didn’t use an axe to change
the gap but instead used one of those funky round plug gappers…junk for
kids to play with. Get a real gapper from a good oily parts house.
It is most interesting to observe just how little stress it takes to hair
line crack the nose. Barely there but it will crack. Side loading on the
center electrode cracked it just enough. Compression and heat finished it
off.
Compression blamed it into the hood liner and bounced down and landed still
in the engine bay. But well hidden.
Regards from
DaveA’s 89 XJ6

: Was it in this list that somebody had to have his car’s head off because
of
: a spark plug electrode deteaching itself from the plug had fallen in the
: cilynder.
:
: (It’s only a question, not an affirmation) Would not then the risk of such
a
: thing happening be multiplied by the number of electrodes?
:
: I need to do maintenance in the Jag (in one month, when I hope I’ll have
: more time, and the sparkies will be changed as well I’d like to try these
: multi-electrode things if there are no dangers…
:
: Thanks
:
: Lluis
:
: 1987 XJ40
:
:
: ______________________________________________________
: Get Your Private, Free Email at http://www.hotmail.com
:

3

Can anyone suggest the best spark plugs for a 2.9 XJ40? I’ve been using
NGK’s but they seem to be breaking down.

Dougie

4

Dougie,
Under what conditions are the spark plugs failing ? I have been using
NGK’s in my 2.9L for some 43k+ miles, so far withhout problems. They were
available at reasonable cost from my source, otherwise I would have fitted
the recommended Champions.
Brett G has reported that more expensive type plugs have not been
satisfactory, in his larger engine variant, and that the recommended
Champion units have proved to be trouble-free. Others, also with the larger
engines, have reported problems with costly plugs as well as NGK’s.

As I write this, I can not recall the precise Champion plugs reccommended
for my 2.9L, (NY3C / 9C ??) but the information is on a clear label set on
the top of the LHS wing / fender valance on my RHD car. Why not try the
manufacturers choice.

Kind Regards,

John Tarrant.

Dougie wrote
<Can anyone suggest the best spark plugs for a 2.9 XJ40? I’ve been using
NGK’s but they seem to be breaking down.>

5

I have Champion rc9yc plugs in my car now…I think that’s the number.
I have never had a problem with them, even when they get very old.

I did try the bosch platinum plugs…single electrode ones.
They set the check engine light, ff26 I think it was.

I tried some sort of NGK v groove plugs, and almost failed
the emissions test, but no codes were ever set.

I tried some ngk platinum plugs, but I think they were the wrong
heat range as they ran black.

I think I tried the bosch plus 4 (4 electrode plugs) and did
not get a check engine light, but no improvement over Champions
and I did not get the emissions tested.

Its interesting to measure the differences between plug brands.
You can measure the resistance with a DMM.

From what I remember, the ngk plugs had a lower resistance
then the Champions.
I should compare them all…

I tend to think its a good idea to replace the plugs every year.
On the AJ6 engine, they are right there, and replacing them ensures
you will be able to get them out, and you can inspect them for
looks.
On some cars that come with 100,000 mile plugs, you may not be able
to remove them without damage to the head after 100,000 miles!On cars with hard to get at plugs, the platinum plugs are great, as you only need to get at them rarely. I would suspect something is wrong if you have a plug that fails in any reasonable amount of miles. I imagine the regular Champions in the AJ6 engine would go about 50,000 miles without trouble. When I got my car, the original plugs were very worn. They MAY have been the original plugs installed at the factory, well worn at 70,000 miles. I took them out and put in the bosch platinum plugs. Nothing but the best for my car! After a week, the check engine light kept coming on. After fooling around with things, I tried the old worn out Champion plugs. No problems at all. It may be that if you gap them, they may go 100,000 miles. They may have only nubs left, but seem to work ok… Brett 1990 XJ6 Dougie, Under what conditions are the spark plugs failing ? I have been using NGK’s in my 2.9L for some 43k+ miles, so far withhout problems. They were available at reasonable cost from my source, otherwise I would have fitted the recommended Champions. Brett G has reported that more expensive type plugs have not been satisfactory, in his larger engine variant, and that the recommended Champion units have proved to be trouble-free. Others, also with the larger engines, have reported problems with costly plugs as well as NGK’s. As I write this, I can not recall the precise Champion plugs reccommended for my 2.9L, (NY3C / 9C ??) but the information is on a clear label set on the top of the LHS wing / fender valance on my RHD car. Why not try the manufacturers choice. Kind Regards, John Tarrant. Dougie wrote

<Can anyone suggest the best spark plugs for a 2.9 XJ40? I’ve
been using
NGK’s but they seem to be breaking down.>

6

I tried the NGK plugs in my '95 XJR - ran as smooth as can be imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put Champions back in,
the idle was never quite as smooth as the new NGK’s, but no misfires after a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle, so I’ll try
those next time.

Cheers - Jez> -----Original Message-----

From: Brett Gazdzinski [mailto:brett.gazdzinski@wcom.com]
Sent: 08 January 2002 14:38
To: modern@jag-lovers.org
Subject: RE: [modern] spark plugs

I have Champion rc9yc plugs in my car now…I think that’s the number.
I have never had a problem with them, even when they get very old.

I did try the bosch platinum plugs…single electrode ones.
They set the check engine light, ff26 I think it was.

I tried some sort of NGK v groove plugs, and almost failed
the emissions test, but no codes were ever set.

I tried some ngk platinum plugs, but I think they were the wrong
heat range as they ran black.

I think I tried the bosch plus 4 (4 electrode plugs) and did
not get a check engine light, but no improvement over Champions
and I did not get the emissions tested.

Its interesting to measure the differences between plug brands.
You can measure the resistance with a DMM.

From what I remember, the ngk plugs had a lower resistance
then the Champions.
I should compare them all…

I tend to think its a good idea to replace the plugs every year.
On the AJ6 engine, they are right there, and replacing them ensures
you will be able to get them out, and you can inspect them for
looks.
On some cars that come with 100,000 mile plugs, you may not be able
to remove them without damage to the head after 100,000 miles!

On cars with hard to get at plugs, the platinum plugs are great, as you only need to get at them rarely. I would suspect something is wrong if you have a plug that fails in any reasonable amount of miles. I imagine the regular Champions in the AJ6 engine would go about 50,000 miles without trouble. When I got my car, the original plugs were very worn. They MAY have been the original plugs installed at the factory, well worn at 70,000 miles. I took them out and put in the bosch platinum plugs. Nothing but the best for my car! After a week, the check engine light kept coming on. After fooling around with things, I tried the old worn out Champion plugs. No problems at all. It may be that if you gap them, they may go 100,000 miles. They may have only nubs left, but seem to work ok… Brett 1990 XJ6 Dougie, Under what conditions are the spark plugs failing ? I have been using NGK’s in my 2.9L for some 43k+ miles, so far withhout problems. They were available at reasonable cost from my source, otherwise I would have fitted the recommended Champions. Brett G has reported that more expensive type plugs have not been satisfactory, in his larger engine variant, and that the recommended Champion units have proved to be trouble-free. Others, also with the larger engines, have reported problems with costly plugs as well as NGK’s. As I write this, I can not recall the precise Champion plugs reccommended for my 2.9L, (NY3C / 9C ??) but the information is on a clear label set on the top of the LHS wing / fender valance on my RHD car. Why not try the manufacturers choice. Kind Regards, John Tarrant. Dougie wrote

<Can anyone suggest the best spark plugs for a 2.9 XJ40? I’ve
been using
NGK’s but they seem to be breaking down.>

Important. This message is intended for the above named person(s)
only and is confidential.

If you are not the person named above or the intended recipient
and have received this message in error please accept our
apologies. Please do not copy it or show it to anyone else. If you
received this message in error, please telephone us on
(+44)(0)1932 404000 or email Helpdesk@Easynet.COM
Then, please delete this message. Thank you.

Because internet communications are not always secure the
recipient is responsible for verifying the origin and authenticity
of the content of this message before acting on its contents. All
contracts must be in writing, signed by an authorized officer of
Easynet Telecommunications Limited. All orders must be placed
on Easynet Telecommunications Limited standard hard copy form.

Please note that Easynet Telecommunications Limited may
monitor e-mails and other communications passing between
itself and any other person.

7

Well it seems that I’ve had the same with my NGK’s because after around
2000 miles, I’ve just discovered that one was completely dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s still spitting
back into the inlet manifold when cold though so I guess my investigation
isn’t over yet!.

DougieDate: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put Champions back in,
the idle was never quite as smooth as the new NGK’s, but no misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle, so I’ll try
those next time.

Cheers - Jez

8

Well it seems that I’ve had the same with my NGK’s because after around
2000 miles, I’ve just discovered that one was completely dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s still spitting
back into the inlet manifold when cold though so I guess my investigation
isn’t over yet!.

DougieDate: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put Champions back in,
the idle was never quite as smooth as the new NGK’s, but no misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle, so I’ll try
those next time.

Cheers - Jez

9

I don’t remember how it goes, but I thought the higher
the number, the lower the heat range the plug (colder)?

I got some platinum plugs that were 12,s and they ran black.

3 steps is quite a jump in heat range, I would keep an eye on them
after trying them.

Hard to imagine putting a hotter plug in an XJR!
I would think they run warm already…

You can run as hot of a plug as you like short of melting the piston
or the plug.
Cold plugs foul out.

Tan to light tan is a very nice thing to see on the working
end of a spark plug.

Brett
1990 XJ6>

Well it seems that I’ve had the same with my NGK’s because
after around
2000 miles, I’ve just discovered that one was completely
dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s
still spitting
back into the inlet manifold when cold though so I guess my
investigation
isn’t over yet!.

Dougie

Date: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be
imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put
Champions back in,
the idle was never quite as smooth as the new NGK’s, but no
misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from
RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle,
so I’ll try
those next time.

Cheers - Jez

10

Brett

The aim is to keep plugs running at between 350C and 750C for optimum
performance.
So the number represents the length of the porcelain nose inside the plug
and I think a “12” is 12mm long which means more area for combustion heat to
impinge on the plug and less for it to escape to the cylinder head than say
a “9” so the plug is “hotter” and should be used in a “colder” engine i.e. a
lower compression or less stressed engine.
As you say, I would expect an XJR to need a colder plug.
If too cold a plug i.e. too low a number is used it will soot up, too hot a
plug (high number) and it will burn away the electrode and foul the tip with
oxides.
Your 12s should not have sooted up but been burnt.

Norman Watkins> I don’t remember how it goes, but I thought the higher

the number, the lower the heat range the plug (colder)?

I got some platinum plugs that were 12,s and they ran black.

3 steps is quite a jump in heat range, I would keep an eye on them
after trying them.

Hard to imagine putting a hotter plug in an XJR!
I would think they run warm already…

You can run as hot of a plug as you like short of melting the piston
or the plug.
Cold plugs foul out.

Tan to light tan is a very nice thing to see on the working
end of a spark plug.

Brett
1990 XJ6

Well it seems that I’ve had the same with my NGK’s because
after around
2000 miles, I’ve just discovered that one was completely
dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s
still spitting
back into the inlet manifold when cold though so I guess my
investigation
isn’t over yet!.

Dougie

Date: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be
imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put
Champions back in,
the idle was never quite as smooth as the new NGK’s, but no
misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from
RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle,
so I’ll try
those next time.

Cheers - Jez

11

Norman,
The NGK web page has it the other way, the higher the number
the colder the plug.

I am not sure if all plug makers use the same setup, but
I got some ngk platinum plugs bkr12evx that were black.
The recommended plug was bkr6evx…

Brett
1990 XJ6>

Brett

The aim is to keep plugs running at between 350C and 750C for optimum
performance.
So the number represents the length of the porcelain nose
inside the plug
and I think a “12” is 12mm long which means more area for
combustion heat to
impinge on the plug and less for it to escape to the cylinder
head than say
a “9” so the plug is “hotter” and should be used in a
“colder” engine i.e. a
lower compression or less stressed engine.
As you say, I would expect an XJR to need a colder plug.
If too cold a plug i.e. too low a number is used it will soot
up, too hot a
plug (high number) and it will burn away the electrode and
foul the tip with
oxides.
Your 12s should not have sooted up but been burnt.

Norman Watkins

I don’t remember how it goes, but I thought the higher
the number, the lower the heat range the plug (colder)?

I got some platinum plugs that were 12,s and they ran black.

3 steps is quite a jump in heat range, I would keep an eye on them
after trying them.

Hard to imagine putting a hotter plug in an XJR!
I would think they run warm already…

You can run as hot of a plug as you like short of melting the piston
or the plug.
Cold plugs foul out.

Tan to light tan is a very nice thing to see on the working
end of a spark plug.

Brett
1990 XJ6

Well it seems that I’ve had the same with my NGK’s because
after around
2000 miles, I’ve just discovered that one was completely
dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s
still spitting
back into the inlet manifold when cold though so I guess my
investigation
isn’t over yet!.

Dougie

Date: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be
imagined for
about 1000 miles, then went to behaving like the old
Champions, then
developed a real bad misfire when starting from hot. Put
Champions back in,
the idle was never quite as smooth as the new NGK’s, but no
misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from
RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle,
so I’ll try
those next time.

Cheers - Jez

12

Brett

Yes you are correct some manufacturer’s numbers go the other way but I still
think that the Champion number relates to the length in mm of the nose
inside the plug.

Norman> Norman,

The NGK web page has it the other way, the higher the number
the colder the plug.

I am not sure if all plug makers use the same setup, but
I got some ngk platinum plugs bkr12evx that were black.
The recommended plug was bkr6evx…

Brett
1990 XJ6

Brett

The aim is to keep plugs running at between 350C and 750C for optimum
performance.
So the number represents the length of the porcelain nose
inside the plug
and I think a “12” is 12mm long which means more area for
combustion heat to
impinge on the plug and less for it to escape to the cylinder
head than say
a “9” so the plug is “hotter” and should be used in a
“colder” engine i.e. a
lower compression or less stressed engine.
As you say, I would expect an XJR to need a colder plug.
If too cold a plug i.e. too low a number is used it will soot
up, too hot a
plug (high number) and it will burn away the electrode and
foul the tip with
oxides.
Your 12s should not have sooted up but been burnt.

Norman Watkins

I don’t remember how it goes, but I thought the higher
the number, the lower the heat range the plug (colder)?

I got some platinum plugs that were 12,s and they ran black.

3 steps is quite a jump in heat range, I would keep an eye on them
after trying them.

Hard to imagine putting a hotter plug in an XJR!
I would think they run warm already…

You can run as hot of a plug as you like short of melting the piston
or the plug.
Cold plugs foul out.

Tan to light tan is a very nice thing to see on the working
end of a spark plug.

Brett
1990 XJ6

Well it seems that I’ve had the same with my NGK’s because
after around
2000 miles, I’ve just discovered that one was completely
dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s
still spitting
back into the inlet manifold when cold though so I guess my
investigation
isn’t over yet!.

Dougie

Date: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow paul.stow@easynet.com
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be
imagined for
about 1000 miles, then went to behaving like the old
Champions, then
developed a real bad misfire when starting from hot. Put
Champions back in,
the idle was never quite as smooth as the new NGK’s, but no
misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from
RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle,
so I’ll try
those next time.

Cheers - Jez

13

The logic for the XJR may be that it is a lower compression engine, so maybe
a hotter plug is better - not sure, but that’s the Jaguar recommendation so
I’ll give it a go and see what happens…

Cheers - Jez> -----Original Message-----

From: Brett Gazdzinski [mailto:brett.gazdzinski@wcom.com]
Sent: 10 January 2002 18:26
To: Modern@jag-lovers.org
Subject: RE: [modern] spark plugs

I don’t remember how it goes, but I thought the higher
the number, the lower the heat range the plug (colder)?

I got some platinum plugs that were 12,s and they ran black.

3 steps is quite a jump in heat range, I would keep an eye on them
after trying them.

Hard to imagine putting a hotter plug in an XJR!
I would think they run warm already…

You can run as hot of a plug as you like short of melting the piston
or the plug.
Cold plugs foul out.

Tan to light tan is a very nice thing to see on the working
end of a spark plug.

Brett
1990 XJ6

Well it seems that I’ve had the same with my NGK’s because
after around
2000 miles, I’ve just discovered that one was completely
dead. Funny thing
is, I put in one of the old NGK and it’s running fine! It’s
still spitting
back into the inlet manifold when cold though so I guess my
investigation
isn’t over yet!.

Dougie

Date: Tue, 8 Jan 2002 15:05:23 -0000
From: Paul Stow <@Paul_Stow2>
Subject: RE: [modern] spark plugs

I tried the NGK plugs in my '95 XJR - ran as smooth as can be
imagined for
about 1000 miles, then went to behaving like the old Champions, then
developed a real bad misfire when starting from hot. Put
Champions back in,
the idle was never quite as smooth as the new NGK’s, but no
misfires after
a
lot of miles.

Jaguar changed the recommendation for the AJ16 engine from
RC9YCC to the
slightly hotter RC12YCC, which is said to improve the idle,
so I’ll try
those next time.

Cheers - Jez

Important. This message is intended for the above named person(s)
only and is confidential.

If you are not the person named above or the intended recipient
and have received this message in error please accept our
apologies. Please do not copy it or show it to anyone else. If you
received this message in error, please telephone us on
(+44)(0)1932 404000 or email Helpdesk@Easynet.COM
Then, please delete this message. Thank you.

Because internet communications are not always secure the
recipient is responsible for verifying the origin and authenticity
of the content of this message before acting on its contents. All
contracts must be in writing, signed by an authorized officer of
Easynet Telecommunications Limited. All orders must be placed
on Easynet Telecommunications Limited standard hard copy form.

Please note that Easynet Telecommunications Limited may
monitor e-mails and other communications passing between
itself and any other person.

14

IT IS LEAN IF IT IS BACKFIRING THROUGH THE INLET ( may also have tight
intake valve clearance if you did a recent valve adjust - very unlikely
though ) - IF YOU DONT HAVE ANY TROUBLE CODES SET _ IT MAY BE A FUEL
PRESSURE PROBLEM ( IE bad fuel presure regulator ) < OTHERISE _ MAY BE A
COLD START MODE PROBLEM _ IE YOUR WATER TEMP SENSOR IS NOT TELLING THE
COMPUTER IT IS COLD _ WHEN DO SYMPTOMS APPEAR ?? DOes it do it when hot ?
Have you snugged up the intake manifold bolts ? May also be a vacuum leak on
the intake side of things …Opps - may also be a cross-firing sparkplug lead
( IE on lead cross-firing another lead either through induction or just
rotten insulation) - how old & cruddy are they ??

BIGGY

15

List,
Last service my garage installed Valeo spark plugs to my cat for experiment if
they are suitable for Jag.Results was bad:at least once per day when i was in
traffic lights engine sometimes missed one cylinder,no good!I checked wires,
good.Then i get back for garage and told Valeos are crap.Then they changed
NGKs back and everything is silky smooth again.I would guess that only good
plugs for XJ40 is ngk or champion at least from my experience?
Rgds:Jukka
XJ40 Sovereign 3.6 -89 MANX 168500km with ngk plugs and silky smooth
idle.

16

Jukka, last time I used Bosch. I used the NGKs in my Infiniti when I had
it - I wouldn’t have thought the Japanese plugs would work that well in
Jags. have you or anyone else had any experience with the 4-pronged bosch
plugs?-----Original Message-----
From: owner-modern@jag-lovers.org [mailto:owner-modern@jag-lovers.org]On
Behalf Of Jukka
Sent: Saturday, April 27, 2002 8:58 AM
To: jag list
Subject: [modern] spark plugs

List,
Last service my garage installed Valeo spark plugs to my cat for experiment
if
they are suitable for Jag.Results was bad:at least once per day when i was
in
traffic lights engine sometimes missed one cylinder,no good!I checked wires,
good.Then i get back for garage and told Valeos are crap.Then they changed
NGKs back and everything is silky smooth again.I would guess that only good
plugs for XJ40 is ngk or champion at least from my experience?
Rgds:Jukka
XJ40 Sovereign 3.6 -89 MANX 168500km with ngk plugs and silky smooth
idle.

17

Thomas wrote:

Jukka, last time I used Bosch. I used the NGKs in my Infiniti when I had
it - I wouldn’t have thought the Japanese plugs would work that well in
Jags. have you or anyone else had any experience with the 4-pronged bosch
plugs?

Both of our XJ40s are equipped with Bosch platinum +4 plugs and Magnecor
wires. No problems after 30K miles.

Dave Lokensgard
'90 Vanden Plas Majestic (DAVZCAT)
'55 XK140 OTS
Poway, California

18

All,
I have no experience of Bosch plugs on Jag but good results on my former Range Rovers(3 ea).Any way the old ngk plugs looked like new when replaced
in sevice and replaced those crap valeo ones.Now i have good ngks back w/o
problems.
Rgds:Jukka
XJ40 Sovereign 3.6 -89 MANX 168500km