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What on earth??? Bizarre Focus problem

Hi,

Like a good mate I offered to service a mates Focus as I'm fairly experienced in such things.

Changed the spark plugs, oil&filter, air filter. Simple you'd think.

Started it up and it ran rough (poor pickup through 1000-2000 revs) and the yellow engine light came on. Just like you'd expect if it was running on 3 cylinders.

On investigation the HT lead hadn't been put back correctly on cyl 4. Perfect answer I thought. But no. Still no better once put back correctly.

I'm completely at a loss as to what on earth I've done wrong. Any ideas? What can cause the light to come on and such symptoms form only touching these things?

More info:

- After driving for 2 mins and getting up to 40mph the light started flashing.

- I cant find any wires that I've dislodged.

- There was an engine earthing wire which was broken, so I reconnected that (before I found it running rough). So I disconnected it again - maybe it was severed for a reason? - but no difference whether connected or not.

- I've put back the original 4 spark plugs - no difference.

- One of the air filter housing bolts needed grinding off, making a bit of a mess of the plastic housing and I've rep replaced it with a zip tie which seem very satisfactory (surely the casing doesn't have to 100% airtight - which it probably is anyway)

-I had overfilled it with oil, maybe 1 cm over the top mark, but after being run for 5 mins I drained the extra out.

Thanks in advance for any help. Steve

Reply to
steveonholiday1
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ooooo.... more info....

If I pull the HT lead off cylinder 4 it makes no difference. Whereas if I pull any of the other 3 off it makes it stall.

But if I plug a spark plug into the HT lead number 4 and earth it to the engine, it sparks nicely.

It makes no sense - what could it be?

Reply to
steveonholiday1

leaving one disconnected will lead to a failed ht lead or coil pack.

Reply to
Mrcheerful

This would make sense. Can the coil pack fail just on one cylinder? (On my old mk2 fiesta - the only engine I know very well) there was one coil pack which powered all 4 plugs, so it was all or nothing.

Also how would this explain the plug sparking ok when laid earthed on the engine?

Reply to
steveonholiday1

The coil Pack is basically doubled ended for each pair of cylinders so actually two coils in one lump, each coil gives a negative spark to one plug and a positive to the other, the coil insulation can break down internally so as to give one really good spark and one really weak one which is blown out and leaks away internally under compression pressure. To prove the point you can swap the leads on the coil and check that the non firing cylinder moves. 1 and 3 are paired and 2 and 4 IIRC

Reply to
Mrcheerful

Ah. OK, I'll try that tomorrow (its raining now).

If it is this, how much is a new coil pack, (and how much from a breaker), and how easy is it to change?

Reply to
steveonholiday1

most car shops have them, around about 50 quid IIRC.

Reply to
Mrcheerful

Difering manufacturers have different set ups , my daughters car has one coil pack but each plug is independantly serviced

Reply to
steve robinson

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