Did this plug melt, or was it co-incidentally defective?

[chris1roll]

With reference to my readers cars thread, long story short:

1989 Volvo 740 running K-jet mechanical fuel injection.

Every 6k or so it would go through a period of running like crap, then at the point I would have time to investigate, it would magically fix itself (just K-jet things!) at which point I'd just carry on.

Most recent episode, it didn't fix itself. I tested the injector spray pattern and one was completely knackered (just producing a single 'jet'), one pretty poor and two 'ok'. Interestingly they were all delivering a similar amount, just not atomised.

4x new Bosch injectors fitted, I now had an almost dead miss on cylinder 4, which at the start of this process, was one of the stronger ones when I was pulling leads etc

Pulled this out of it, 7.5k miles on the correct NGK's bought from ECP:




It's hard to get a decent picture with a phone, if anyone's reallyinterested I'll see if I can dig out the actual digital camera.

Anyway - Is it possible to melt just the centre electrode and leave the ground electrode untouched?

Someone else suggested it was defective and had simply broken off?


Just out of curiosity really, as with a fresh set of plugs it is now running more smoothly than it ever has in the previous 3 and a bit years/32k miles I've done in it, so I've got away with either not burning a valve as well, or the bit of electrode swiftly found it's way out of the exhaust.

The exhaust actually smells 'nice' now too.

[hidetheelephants]

It's broken off, no way that's burnt away. No doubt there may be some dents in the piston crown, but debris that small will have been blown out quickly.

Edited by hidetheelephants on Friday 2nd October 23:20