Outer Limits 4x4 Board

Further to the posting re TopGun leads, I have had similar experiences with them in my 2000 NL Pajero on gas. In fact, I blame them for the start of the problems. I went to 105000 km on the original plugs (NGK PFR6J 11) and leads (NGK). No problems at all. I replaced the plugs with more NGKs and at the same time, put new Topgun leads in. 10000 km later, massive backfires, airflow meter stuffed and other problems. When I lifted the bonnet at night, you could see all the leads glowing in the dark and shorting to earth and to each other. The insulators had melted onto the spark plugs and I had to abandon the whole lot.

I got a set of Bosch leads and put them in. Bosch are OK, but they are not numbered and they are not the right lengths – they are marginally too long and this means that you have trouble in getting them to lay out without crossing (and touching) each other. The leads lasted until 200000 km, when I replaced them and the plugs. I used NGK for the leads and plugs this time. Part of teh problem is that the insulation on the leads is only 5 mm diamater and all the coils and mounting clips are designed to take this size only. It is far too light in my opinion.

I got a crook batch of gas recently and the engine started massively backfiring again. Once the insulation on the HT leads is penetrated (by the spark) they are useless. I suspect that in my case, the leads did not break down to earth, but rather to the adjacent lead. If, when say No 1 plug fires and No 3 or 5 inlet valve is open as part of its stroke, the damned spark can jump to that particular lead and you get a backfire. Since the inlet manifold is full of gas, the bang is quite large, especially if you are at 3000 r/min and at full throttle climbing a hill. Airflow meter and aircleaner box all cop it badly.

Since replacing the leads and plugs on my Pajero takes several hours, and I go to remote places at times, I wanted to get things right so I did a lot of research this time around. For the leads, the choice was Bosch or NGK. Since the NGK leads had let me down (after I had removed them a few times chasing another problem), I chose Bosch with a stainless steel core.

For the plugs, I chose NGK again, but a heat range colder this time. The original plugs are PFR6J11. They are platinum plugs. These plugs have a central electrode 0.6 mm diameter. I opted for NGK Iridium plugs this time. The central electrode is 0.4 mm diameter and that is THIN. My main concern is “How long will they last?” The plugs I used are BKR7EX-11. Note that with NGK, the colder the heat range of the plug, the higher the numbering system. This is different to the other manufacturers. Incidentally, the heat range of the plug also tends to affect the melting of teh lead insulator onto the plug, so the colder plugs may hopefully cure this problem as well.

One of the reasons I went for the Iridium was that NGK claim better performance and better economy. Well, I reckon that they are right and this is not a placebo effect. I just came back from a trip and did 1516 km, using 230.1 L of gas. This comes to 15.2 L/100 km. Prior to this trip, I was using about 16 L/100 km. The trip was nearly all at (or slightly above) the speed limits – mainly 100 and 100 km/hr. Having said this, I have also replaced the plugs and leads in my wife’s Magna 3L manual sedan, but so far, we have noticed a a marginal but not really significant gain in performance or economy.

I could not find any references to the plugs I used in Australia, so I bought them (and the leads from the USA. Apart from being significantly cheaper, they had a much wider range of product to choose from, and delivery was similar to what I would have received if I bought from local suppliers.

Anyone else had simliar or better experiences with plugs and leads?

NGK is the only brand of spark plug I use and I have fitted literally thousands of them over the years. According to NGK the Iridium IX has a service life of 60 000km. As for leads, often it is hard to go past genuine leads, though it does vary between manufacturers.