Mis-firing when under load

[Howhardcanitbe?]

I have a 2006 ford Ka, recently when I have accelerated relatively hard (pulling out of a busy junction for example) the engine faulters as if it's not firing on all cylinders. On idle it runs smoothly and if I rev the engine in neutral it also runs smoothly. It only faulters when the engine is under load and seems to be between 1000 & 2000 rpm. If I accelerate slowly this problem doesn't occur. I have replaced the HT leads with no effect and been told (and by experience) it doesn't appear to be a fault with the spark plugs. Also I have not had any warning lights come up. Hasn't lost any oil or water and no sign of a leaking head gasket. Has anyone got any ideas as I do not have the money to keep throwing at it and cannot afford a new car.

[Stoney871]

Coil pack?

Sent from my SM-G965F (S9+)

[isetta]

I would put a code reader on it. Not all codes cause light to come on, it might show a code for misfire on a particular cylinder which will narrow it down

[Howhardcanitbe?]

Thanks for the response, I changed the spark plugs which seemed to improve the problem but not entirely. As previously suggested next option is the coil pack. (a relative has the same car and symptoms sound the same as a coil pack fault on theirs). I don't have a manual and I know this is a stupid question, but how do I know which one to get? I have had a look online and there are a number of these for sale - they look identical but have different reference numbers (?)