[g259fsg]

I’ve had some problems with plugs this year. I started to get some misfiring in the spring around the time I suspected HGF. I think that was coincidental. I found one of the plugs was black and not firing properly and there were streaks up the insulator – probably arcing inside. These were Bosch FR78X which have four earth electrodes in a star shape. They’d been in 6 years (13,000 miles) and seemed to work fine, so I got a new set. The first lot were made in Germany, the new ones in Russia! Anyway, a few weeks ago I started getting misfiring again, also a bit of loss of power and a more noisy exhaust. One of the plugs was black again and another didn’t look too pretty. The other two were grey. I replaced them with two good German plugs I took out in the spring. Everything fine then, though it did improve further with a bit of driving. Probably the cylinders were a bit coked-up.

I now had a mixture of slightly suspect Russian plugs and old German ones. I’ve replaced them with Champion Long-life Platinum Plugs (3344) supplied by DMGRS who have a set of four at quite a good price. They do seem very good indeed, even better than before. Most noticeable at low revs., where the engine seems to pull better and more evenly. Less noise and more power. Hope they are long-lasting and I won’t have to return to this problem. I did have some Champion long-life plugs (EON 2702) years ago and they did well for more than 30000 miles.

From experience so far, I would definitely recommend the Platinum Plugs in the K Series engine.

[Stan Thomas]

Your H.T. leads might be going "high resistance", which they will do with age.

Standard carbon trace H.T. lead (not early copper core wire) is 16K ohms per metre, so check your leads which should be around 5 to 6K ohms.

Regards to all.

Stan.

[Johnny 216GSi]

I've got Denso IK20 Iridium electrode plugs in my cars. Not cheap, and they don't improve either fuel economy or power/torque feel, at least not much I can feel. And given the electrodes are so fine, they are past their best at 20K miles!

I say no extra power, but I've yet to have a new power plot after the Terraclean, Iridium spark plug fitting and K&N panel filter. I'd suffered a bit of engine coking and I was about 3 Nm down on torque but spot on for power and the torque, and the power peak positions were spot on too (within 50 rpm of the quoted peak positions as specified by Rover).

[g259fsg]

Good point about the HT leads from Stan. On the old cars I usually make my own using copper-cored HT cable, but for the Rover like most others I'm sure, I use manufactured leads with the deep plug connector. The current ones I'm using are about 5 years old, Prospark. Are they good? The other problem part on ignition is the distributor cap and rotor arm, particularly the rotor arm which can suffer electrical breakdown across the insulation. I've had trouble with cheaper after-market parts, and last time opted for genuine LR parts from Rimmers.

I agree that there shouldn't be any significant difference between good plugs when it comes to performance. I can't compete with the specifics of the rolling road test. I guess in my case it was because I'd had a bit of substandard ignition that the Platinum Plugs did seem better. It's subjective to some extent, but when you've had a car for a very long time, you can tell very quickly if anything changes even slightly. When ignition takes place, it doesn't just go bang, there's a flame front that travels forward from the plug probably in fractions of a millisecond. If the ignition is degraded and there's a weak spark, the flame front might be slower. My impression was the engine was a bit more responsive at low revs and always sounds even. Seems to pull away better without revving the engine.

[g259fsg]

It's a while since I started this thread, and our 214 has been enjoying the long-life Champion plugs until a couple of weeks ago when I started getting misfires again. Initially, quite infrequent and usually when the engine was cold or when climbing a hill in second. It's got progressively worse. I remembered Stan's comment about modern ignition leads going high resistance after time. The current ones have been on the car about five years. I got them from Euro Carparts, not a recognised maker like Lucas or Bosch. The source of the problem became rather obvious when I tried removing a spark-plug lead with the engine running. Three of them made a pronounced discharge noise in the spark plug tube as I pulled them off, but on No.1 there was no sparking, just the sound of the engine running on three cylinders. I took it off and measured the resistance - completely open-circuit. Enough HT was getting through to fire the cylinder most of the time. The others read 10k to 15k ohms. I keep a couple of spare ignition leads in the box of tricks in the boot. Fitted one of these and the problem went away.

[Paul_1978_yorks]

That reminds me, I must check my plugs this year, not sure I've had them out since I bought the car 3 years ago so they could do with checking. Might put some iridiums in and get a new set of leads.

[Dorchester]

I've put several kind of plugs in my 25 and my cabby and TBH I haven't noticed any sensible difference (torque, power, mpg...) provided the rest of the engine is in good nick.
I've just bought and put on the shelf 2 sets of DENSO IK20TT Iridium for later, i.e. 2024 for the cabby and 2025 for the 25 (I use to swap them every 5 years).
BTW I've just fitted DENSO VK16G Iridium in my 75 V6. I'm always trying to buy quality item (oil, filters, coolant, tyres you name it) and never regretted it.
But time will tell.