OK so I've searched on here to find out. What iridium plugs people use. There's a lot of talk about using standard Champion or NGK plugs and not wasting money on fancy expensive plugs that don't improve performance. Wait a minute, I thought iridium plugs had a longer life span 100,000ks compared to 25000 for standards?? Considering the hassle and potential for additional dramas in replacing the plugs I would've thought the expense would be justifiable. And if you buy from the right supplier the expense is minimal anyway

Thoughts?
And what iridium plugs are people using in their HE's?

 

Hoppy, this has been debated over and over and over ( use the Forum search feature) it's right up there with an "oil" or "Leaper vs growler" thread. Ps...I run NGK Irridium.

 

I run denso IT20TT

 

When I purchased my XJS it had iridium plugs in it. I drove it home, about 400 miles, and my check engine light came on 4 different times during my drive. I wrote down the code and reset the light. I got the same code all 4 times. When I got back I took the car in for a pre-purchase check on the next Saturday at Hennessy Jag of Gwinnett. The service manager and I did the check. One of the things he noted was the iridium plugs need to go,it was causing my misfire code. He said the ignition system was designed to use the standard resister plug, as in the owner’s manual, it was not optimized for the more expensive plug and would lead to inconsistent spark. That was the first thing I replaced the very next weekend and have not had a misfire code since.

 

Interesting. I am surely not going to quarrel with your experience with the Jaguar Service Manager.


But, why intrigues me. Does the irradium increase the spar plug's resistance. I can almost realize that an increase to a point would act as a capacitor and allow a build up for a stronger spark. But, only if the ignition system could deliver increased voltas to allow that.


If not, stacked resistance values sure could create misfires. Resistor Plug & resistor HT wires I all he stock ignition unit can handle.


Variable. OK with fresh HT wires, not so with aged wires and higher resistance.


So, as you did, go with what works.


Carl

 

I gotta call BS on your service manager, ran Irridiums in my 97 4.0 XJ6L for 3 years and it never skipped a beat. More likely whatever the problem seas (loose connection etc) was resolved during the plug swap. The ignition system could care less about "standard" "platinum" etc. now here's where the fun starts...."Jags only run on standard Champions etc" BS, been running NGKs and Iridiums in everything I own INCLUDING my TR-6, Bonneville etc, zero issues.

 

The service manager and I removed the plugs to do a compression test and reinstalled the same plugs. That would have solved any loose connection theory.I received another check engine light after that and before I replaced the plugs myself. It was the same code and now I have had the car 4 1/2 years with no reoccurrence. It could have been the brand of plug (Autolite), but why not stay with what works. My 95 XJS has the same AJ16 as your 97 XJ6L. I run platinum plugs in my 99 XJ8L with no problem.

 

May have been the brand, simply a bad plug (it happens) I can say that I stick with NGK for the reasons you stated, they work for me. In the V-12 I'm going for longevity which the Iridiums provide. It's not a job on that car you want to do often.

 

i use Iridium NGK also, so far 3years , starts quicker and seems smoother!

 

I've ordered the denso iridium plugs from Rockauto. Cheaper than the standard plugs bought locally. They claim 100,000miles+ so will outlast me on this car. Will report back once installed and run

 

I will be very interested to hear how they work. My only worry with a longlife plug would be if I could ever get them out after (say) 50,000 miles!
Greg

 

Iridium plugs are pretty much standard on all modern cars. OEMs started using them strictly for their 100K+ mile life as this helps assure that the engine will stay within emissions limits. Electronic ignition as a whole came along in the '70s for pretty much the same reason.

Removal after 100K miles doesn't seem to be much of a worry, it seems.

 

Same here. My V12 got NGKs as soon as I had the chance. My X308 runs on NGK Irridiums. My former X300 had NGK Irridiums and my C30 had - against Volvo recommendations - you're right, NGK Irridiums. Every car I had I fitted - against recommendations - NGK plugs and if possible/afforderable Irridiums. Not once have I had any sparkplug related issues in more than 500.000 km of driving...

My guess is that one of the plugs or so wasn't fitted right or was loose or so... Nothing else.

 

We all tend to draw conclusions based on personal experiences. Including dealership service managers. I know, because I used to be one


I would be very interested to know if this statement could be backed with an actual technical explanation or if it was merely a conclusion drawn after having seen some problems with some cars fitted with the iridium spark plugs?

Years ago, in my dealership days, Bosch introduced some new razzle dazzle sparkplug. The specifics are long forgotten but the marketing must've been very convincing as several customers asked us to install them. We did. Three of the cars came back with misfires. Reinstalling factory brand/spec plugs solved the problem. I have no idea whatsoever why the problem occurred. Frankly, I didn't care. A forensic investigation as to why an aftermarket product failed to meet expectations wasn't within the scope of my responsibilities.

Since my goal was successful repairs, fewer "comebacks", and fewer unhappy customers I made the business decision that we wouldn't install that type of plug in the future and, if asked, I'd simply explain that we had some problems in the past. If I wanted to sound more official I could very easily have said "The ignition system isn't optimized for that type of spark plug".

All that being said......

On my many personal cars (and boats, and lawnmowers, etc) over the years I can't recall having any problem with any particular type or brand of spark plug. Iridium, copper, kryptonite, plutonium, whatever . The only problematic plugs I've come across personally have been those cracked, dropped or otherwise damaged....usually by me !




Cheers
DD