Wish I'd read this thread last week BEFORE I'd replaced coil/cap/leads assuming that the virtually new RUSSIAN made Bosch plugs were OK
Van was misfiring very badly (I'm ashamed to say I've only just re-started my nearly a year long journey to get my van back on the road after a winter break). The plugs were replaced in the autumn with new Russian Bosch plugs while I tuned things up and did a coolant change and some other repairs. They were understandably a bit sooty (after various start-ups, driveway reshuffles but no long runs) but only a thin coating, so I assumed they were still good. The coil/leads/cap all looked fine and tested out OK resistance wise but I bought new ones in hope that this would help but it made no difference. Luckily I investigated the plugs properly before I moved onto hall sender etc. The insulation resistance across the plug was about 20k ohms on two of them, and about 100k on the third - and they were resistive "R" types so 5k of that is built-in to the plug! No wonder the spark was bad!! I found some old sooty (German Bosch) plugs and checked those - infinite insulation resistance. Swapped over and it's running on all four again. I tried cleaning the Russian plugs with a plastic brush, wiping clean with meths. They cleaned up pretty well with minimal effort but the insulation resistance increased wouldn't get it above 100k, so next to useless!! - perhaps the insulator is bad quality and allows carbon to build up bridging to the electrode?
They were cheap, but I'd bought 2 sets, trusting in the Bosch name. All now heading for the bin. Can only assume Bosch took the Russians at their word, something the world has hopefully learned to never do again.
