Fine when cold,but misfire when hot

[Verity]

Hi all,

I seem to be going round in circles at the moment! As mentioned in another post - 'sounds like running on 3 cylinders' - I was having problems with spluttering and misfiring after a service. Since then I have replaced the HT leads and the coil pack (as well as several other bits around the car).
On short journeys everything is perfect and the car is running spot on, but now that I'm back to work properly and on longer journeys, the car is back to misfiring and spluttering, most noticeable under acceleration. I plugged her into a little cheap handheld obd and it came up with cylinder 4 misfire! :|

Visually everything seems in order, but a friend has said that depending on the age, it could be the temperature sensor. My Puma is V reg,1999 I believe.
Can anybody shed some light on this or have any other suggestions?

Many thanks
Verity

 

[tractorboy]

Have you replaced the spark plugs?

Bob

 

[tuonokid]

As Bob says but also check that there is no oil around the plugs as caused by a leaking rocker gasket. The only other thing I can think of is did you replace the coilpack with a cheapo Ebay one or a genuine Ford one as the cheaper ones can fail at low mileages.
Barry

 

[Verity]

Yes Sir, the spark plugs were changed 300 miles ago when the service was done by Ford. The coil pack was off of ebay and the name on the pack is MotorCraft, which was the name on the one which I took off.
What is the Ford version of a coil pack? I would love to ask at the local dealers but they've been rather rude and very unhelpful and frankly I would feel better if I slapped one man in particular upside the head!
Verity

 

[YOG]

"Ford" parts are normally the same as fitted to the original vehicle. "Motorcraft" are Ford approved parts, not necessarily built to the same standards. Citroen, amongst other manufacturers, operate a similar system.

 

[oilburner]

If the plugs,leads and coil are all ok then I think you need to get a compression test done

 

[Verity]

:-(
compression test sounds so......bad!

 

[killerpuma]

+1 on the compression test an a cylinder leak down test, an if everything else is checked to be ok, there could be a chance of a weak valve spring an once hot enough gets loose enough to notice a misfire, its not common though but can happen

 

[oilburner]

The coil pack has already been replaced

 

[Stavros34]

Could be a leaky injector. Take the fuel rail off with the injectors attached and prime the fuel pump with ignition 2. Don't start it for gods sake. If you get any fuel dribble out of an injector replace it.