Hi,
I know there are many opinions on spark plugs so seeking some thoughts here.
I have a 1995 6.0 with 85k miles. All original and a regular driver, but not daily and all items are working, today...

I have only had this 6 months and decided I wanted to change the spark plugs (yesterday). I did not have to much trouble and 1.5 hours seemed reasonable. Cleaned in the V and air blasted the socket holes. Removed throttle spindle and found I did not need to loosen/remove the AC compressor. That seemed like a task in itself A short spark plug socket with a hex head allowed 1A/B to be removed with no problems. A longer socket and wobble drive took care of the rest. While there, I did the Marelli Rotor shaft modification although the rotor and cap were less than 3k miles old from last owner. Good to have records. I cleaned cap and wires and all runs OK after the change. Gaps set to 0.025"

So, opinion question.
I could not locally find 12 of BR7ES (straight resistor copper core) at the time (yesterday). With some searching I did find that the autolight AP103 was listed as equivalent and that the Motocraft SP-479 (AGSF22WM) was listed as equivalent to that. The reverse matches were not listed but I think that as 1 = 2 then 2 = 1.
Seem to be tough to find true equivalent lookups.
Side by side they seemed the same.

NGK 5122 BR7ES Nickel Spark Plug

AUTOLITE 103 - Alternative spark plugs

Autolite AP103 Single Platinum Spark Plug


So, does anyone have any opinion or cautions about using the SP-479 platinum plug in the 6.0 V12? Price was the same or less than the BR7ES copper and should last longer.

What should I watch out for?

 

The Jaguar dealer told me to stay with the plugs listed in my manuals. Reason I asked them, I was receiving misfire codes when I drove it home from purchasing it out of state. I got poor mileage on that trip as compared to out XJ8L on the highway. The dealer said that the ignition system was designed around that champion plug (copper core resistor plug) and the high end iridium's just would not produce the spark intensity. I replaced the plugs with the correct ones and have not had a problem since. Quicker starting, better idle, and a little better fuel mileage then before. (21 on its maiden trip home VS 24 highway now)

 

Thanks Ron,
I will give these a try and fall back to the originals but pre plan the purchase prior to fitment next time.

YOu get 24 mpg hwy? What speed is that?

 

On my wife's 99 XJ8L (4.0 V8) we set the cruise at 70+, just under the ticket zone, and routinely get 23.5 to 24.5. My wife averages 18 in town driving with no interstate driving. I get 16 on hers but my foot is bigger...My 95 XJS (4.0 AJ16) gets 24 when I keep my foot out of it cruising at 70+, again just out of reach of the fast driver's award. In town I get 15 to 17 driving back and forth to work in Atlanta metro traffic. Both cars on hi-test.

 

I recently had an ignition tuneup done on my '89 XJS, NGK Plugs, new Rotor, Dist. Cap and good quality wires, and though I'm only relying on the trip computer, a 988km road trip to Nova Scotia last month showed 20.6 mpg, and this was 60% 4-lane driving at 110 to 120 kph (60 to 70 mph), and probably 20% more "spirited" driving through a nice rolling, gentle curving route.
I certainly didn't buy this car for gas economy, but I'm more than satisfied with it's performance and mileage.
-I only wish it was 4 or 5 speed Manual, for more fun.

 

Thank you all - hope this helps.
Thank you all for all the information to make this a good adventure in Jaguar owning.


So I thought I would share something that is probably embarrassing but I could see it go un-noticed.
Short Story: Cyl 6 and Cyl 5 coil wires are really easy to mixup.


1995 Jaguar XJS 4.0 6 cylinder AJ16
24K miles.
Was changing spark plugs, because fuel consumption was sub par / could feel it wasnt purring exactly right.
NKG copper -- tried .025 and .03x gaps -- rough idle, returned them.
The Champions I had in there were actually not bad, but they were gapped by last owner at.035.

Put the original champions in -- rough idle.
Changed them to .025 gap, and cleaned everything.
-- rough idle.

Stood there and realized that #5 wire and #6 wire to coils are same length, and #5 (so it turns out) actually came out of the harness behind the #6 wire.

So that's it. not only was this solved by switching #5 and #6 wires, but at .025 gap... .. well its just right, and gunning it, it was a whole new beast.


GL,
David