Ford Ka Misfire - grogee

This is surely the future of home-mechanicking... look it up on the internet!

Anyway: my girlfriend has a 1999 Ford Ka, and very nice it is too. However, it's recently developed a misfire, which manifests itself when the engine is hot - ie. in traffic.

Recently, it had a similar problem which was easily solved - a quick look at the plugs showed that the ceramic casing on No.1 plug was cracked, hence spark was arcing to earth. Rubbish Motorcraft plugs!

Replaced with Champion 'Ion' plugs, which claimed to have a long lifetime - so they should at £5 per plug!

Anyway, the plugs look fine this time, but the misfire is back - any ideas? I am reluctant to shell out for a set of HT leads (does anyone know how much they are?) especially since the problem seems to be temperature related.

There are no warning lights, the coolant level/colour is fine and the rad fan is also fine.

On the subject of taper fit plugs: I have always been told to install any set of plugs with a smear of copper grease on the threads, after gapping the electrode of course... Also I think the best rough guide to fitting taper fit is to tighten them until the taper 'seats' and tighten a further 1/4 of a turn.
Ford Ka Misfire - grogee
In answer to my own question (!):

I replaced the HT leads. Initially got some replacements from Halfords, they were £25ish but guess what - they didn't fit.

Took them back. (Here's a scam: buy plugs and leads at Halfords, get £5 off. Take back the leads, and get refund at full price! Result: you're £2.50 better off!)

Phoned up Ford. Had to wait a day for leads, costing £36 for a set. Collected them. 1 lead was of the wrong type; still haven't got round to taking it back yet. The stupidity of parts collectors/warehouse staff never ceases to amaze me - how can you pick up 3 near-identical leads, and one odd lead, whilst collecting a set of four!!??

Replaced plugs and leads. Car running fine now.
Ford Ka Misfire - Blue {P}
A mate of mine had a horrendous mis-fire on his Mondeo, and I mean really bad, so much so that he thought the car was just about finished, replaced the HT leads and car is now running perfectly!

£36 seems fairly steep, I think we only paid about £5 for Bosch HT leads for his old Escort (RIP), shame they didn't do much to revive a car that should have been declared dead long before he bought it!
Ford Ka Misfire - Andrew Moorey (Tune-Up)
If Mondeo man doesn't replace the plugs as well he will be back to square one in a matter of weeks as the original leads will have burnt a track to earth down the side if the plug(s). The new leads will temporarily sort this until the burnt track down the plug encourages the new lead to fail again.