[x300] Spark Plug Nightmare and question about RC14YC Plug

X300
1

uI Decided to change my spark plugs as a preventative measure this
weekend. The Autolite standard copper plugs I had in the engine
were working fine with no problems. I decided to try platinum
plugs. Since I have used autolite plugs in many of my cars with no
problems, I decided to try their single platinum plug(3924 I
think). I wanted to try platinum for the simple reason they last
longer. I know platinum will bring about no performance difference.
I bought the plugs and installed them. I drove for a while and
noticed that the car had an intermittent miss at idle. I didn�t
suspect the plugs since they were changed. I checked the MAF and
the injectors and the coils. I did and OBD II scan. No Codes. The
miss was getting worse. I decided to pull the plugs and look for
fouling. No signs so I checked the gap and reinstalled them with
new coil gaskets. Still just as bad at idle. I then pulled the
plugs and tested them, they all seemed to work fine in my lawn
mower. Having ripped half the engine apart, including the throttle
body, I gave up and took the plugs back and bought the champion
RC12YC plugs. I gaped them and put them in and they worked fine. No
miss at idle and no hesitation. Looking in to spark plug design as
a chemist, I remembered that platinum does not carry electricity as
well as copper. In fact if I remember, its much worse with
electricity. It is a stronger metal. I like autolite plugs but it
appears to be a compatability problem. I am wondering if the added
resistance of platinum was enough to limit the spark effectiveness?
And if changing to hotter plugs helps idle, has anyone tried the
RC14YC champion plug ,slightly hotter than the RC12YC recomended. I
don�t know how much hotter it runs exactly or if it would damage
the coils due to the added heat? I know now that I will not try
platinum plugs again. Any thoughts?

Jerry
1996 XJ6 100,000 miles–
JMD123
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

2

In reply to a message from JMD123 sent Thu 4 Nov 2004:

If the RC12YC’s are working well, what are you trying to accomplish
with the RC14Y Champion plugs?
Regarding the idle problem you had with the Autolite plugs, were
they of a heat range comparable to the RC12Y’s? If you recall the
reason Jaguar changed from the RC9YC to the hotter RC12YCC’s was to
cure a lumpy idle.–
The original message included these comments:

I bought the plugs and installed them. I drove for a while and
noticed that the car had an intermittent miss at idle. I didn�t
body, I gave up and took the plugs back and bought the champion
RC12YC plugs. I gaped them and put them in and they worked fine. No
And if changing to hotter plugs helps idle, has anyone tried the
RC14YC champion plug ,slightly hotter than the RC12YC recomended. I
don�t know how much hotter it runs exactly or if it would damage

–
uncle
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

3

In reply to a message from uncle sent Thu 4 Nov 2004:

The heat range was the closest to the champions on the autolite
plugs. I am thinking if idle gets better with hotter plugs, would
the slightly hotter RC14YC plugs be any better. Don’t get me wrong,
my idle is fine now. But could it be better? It’s just a
hypothetical situation.–
JMD123
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

4

Hi, did you change to the RCY14 plugs as I was thinking the same ! After checking my plugs with a wear guide it would also suggest a hotter plug !