New Spark Plugs

[FrankGalvin]

I recently bought an old banger at auction and, as the engine was running very rough (misfiring, losing power), I changed the spark plugs. Although the car had been starting without any problem with the old plugs, after a few minutes it would start to misfire and power would decrease.

I changed the spark plugs and the problem was cured - for about an hour.

The plugs should already be gapped correctly, and I followed the instructions to hand tighten and then give it another 1/2 - 3/4 turn. Originally I gave them a 1/2 turn then refitted giving them a 3/4 turn but still misfiring.

Any clues? It has to be something to do with the plugs since changing them originally cured the problem - albeit not for very long.

[TWR]

Depending on the year of the car, Coil Pack, Leads, Do not take it for granted that the plugs are PRE-SET always check them, are the plug a good make? have you checked the timing? did you FULLY service the car? did you change the fuel filter? are the plugs +leads Tracking? Check this at night! with the car running can you see sparks from the Ign leads in any area around the plugs, Head area?

[FrankGalvin]

Thanks TWR.

The plugs are NGK (which I believe are a good make), but I'm not that good at mechanics, though keen to learn.

I'll buy a set of feeler guages to check the gap, and I'm going to replace the coil and leads later today. I suspect that it's the coil since the misfiring is intermitent. The car sometimes misfires from startup and then 'jumps' to normal, or vice-versa. Like I say, the misfiring is intermitent, so I wouyldn't think that timing would be an issue - but I'm no expert.