I have a 2008 focus, it recently started running a little rough with a slight misfire so I’ve changed the coil pack and spark plugs like for like. Noticed some oil on the plug nearest the coil pack and figured I’ll let the garage look at it. However, the misfire is now 10x worse and the car practically undriveable. Next to no power in first, shaking and engine cutting out. I numbered the leads before I took them off to ensure they all went back on correctly so I know they are on right. How can I have made it worse? And more importantly how do I rectify it because I doubt it would get as far as the garage at the moment. 

Sounds like at least one lead hasn't been refitted tightly.  Pull them out and reseat them.  If that doesn't work, check the spark plugs are all at least hand tight.  If still no better, refit the original coil pack.

Also, may help future posts if you put the engine size.  I've made an educated guess that it's petrol.  

7 hours ago, TomsFocus said:

Sounds like at least one lead hasn't been refitted tightly.  Pull them out and reseat them.  If that doesn't work, check the spark plugs are all at least hand tight.  If still no better, refit the original coil pack.

Also, may help future posts if you put the engine size.  I've made an educated guess that it's petrol.  

Hi sorry, yes it’s a 1.6 petrol. I’ve removed and replaced the leads several times, will go dig in the bin for the original coil pack and refit that. Appreciate the advice. 

You could've bought a dodgy coil pack.

Or, you didn't change the leads and the leads are that worn that they can't cope with the new coil pack

I would put new leads on first, before swapping the coil pack out

But, also, make sure you have the right leads on the coil pack on the right spark plug and not mixed

In the dark with the hood open, running the engine can sometimes exhibit sparks if the high voltage is tracking. Could be so many causes, have you had any diagnostics run through the OBD ?

5 hours ago, RL123 said:

In the dark with the hood open, running the engine can sometimes exhibit sparks if the high voltage is tracking. Could be so many causes, have you had any diagnostics run through the OBD ?

Not yet no, it won’t get to the garage in the state it’s currently running in. 

16 hours ago, Nebema said:

Not yet no, it won’t get to the garage in the state it’s currently running in. 

The  DTCs will tell you which cylinder is miss-firing though, you need to know

Sounds like more than a single misfire, with coil packs is the firing order defined by the lead positions as per the older distributors.

if so check the firing order.

good luck

Just looked on the web and it may be the the plug leads into the coil pack have to be in the correct positions. Two coils generate the spark and feed to two lead positions alternatively hence if they are refitted wrong, the engine won’t run or very badly.

just a possibility, hope you changed them one at a time or they are labelled.