I have a 2003 Mondeo Estate with a 1.8L Duratec petrol engine which recently has started misfiring. The misfire appears to occur between 1500 and 3000 rpm and is more noticable during gentle/normal acceleration and less so under hard acceleration. The fault appears to have started after changing the spark plugs, but the plugs look to be working OK. Engine management light now on and looking to see if I can get the error codes read.

Any experience of a similar problem and how it was fixed.

Many Thanks

Alan

very common for ht leads to play up sfter putting new plugs in, never could get my head round why, but had it myself a number of times on fords and know a number of others that have experienced the same..

I think its basically due to the HT leads breaking isnt it?

The HT leads have sat happily where they have for years on end, the wires become used to were they are positioned, the weather and conditions all play a part on making the wires a bit more fragile, but as they are not moving, they are in a secure placement on the plugs. Then, we come along and spoil it for them, we remove the leads the now more brittle by age and posture leads are suddenly bent around, and moved from their comfortable and secure position thus breaking the wires within and making for a worse contact. Then, you reconnect them back exactly as they were, but because they are now fractured, or bent out of posture, they dont feel comfortable and dont have the thorough connection that was once there, thus resulting in a poor connection and reliability.

I tend to imagine it as a road, all's nice and smooth for years, then some begger starts digging holes and filling them in, that once pristine road is now full of dips and bumps (and more often than not - potholes!) and as a result the entire driving experience is ripped up and spoiled...

its the obvious answer, but when you take extra care in removing the leads as you've been caught out by this before, then it makes you wonder.

weird thing is, i tend not see this problem as much as i used to, but that could be down to either not working on as many of them as i used to and/or ive replaced the leads in the past with possibly a better quality set?????

bearing in mind the extra care i took in removing them, but still suffered the problem 4/5 times out of 10..it made me think the leads were breaking down anyway, just seems weird they show up a problem on new plugs but were fine on the old ones...would have thought they had to work less on a nice sparkly new plug?? :)

the other thing i forgot to add about the OP...did you ensure the plug gaps were right?

true point Tony!

over time though you probably subconsciously removed them carefully to prevent extra damage?

Thanks for the quick responses and agree with your comments. My gut feeling was leads/coil having just replaced the plugs, but was getting some messages that it could be throttle position indicator or mass flow indicator. Just got a friend with an OBD machine and shows up fault as P0302, which translates as a misfire on cylinder 2. So now switched the new plugs to see if its the plugs and then heading down the leads/coil route. I'll let you know the outcome.

Many thanks fo the help, appreciated.

Alan

check there is no water inside by spark plugs. sounds silly but this was a nightmare in my old focus. poked down kitchen roll (strong stuff?) dried them out best I could without removing them sprayed a little WD40 in replaced leads worked a treat.

Problem now looks fixed. I took off the coil and on the underside there was a lot of black dust on the cyclinder 2 and 3 side. Cleaned it off and the resin still looked slightly blacker inside and also a short crack inside the resin. Failure on the cylinder 2/3 was consistent with the OBD misfire code on cylinder 2. Replaced the coil and leads and now working fine for a week. Looks like an earth fault between the cylinder 2/3 coil, causing the darkening in the resin and the static concentrating dust on the outside of the base of the coil. Failure was probably confirming the plug leads were still firmly connected at the coil after replacing the plugs and the plastic and resin being fragile.

Very grateful for all the quick responses.

Alan

glad your sorted.

as for cause, chances are it was the leads..if a spark breaks down in the lead, it doesnt just stop, it finds the easiest route to short out..in your case, probably the coil..once it does so, even with new leads, that tracking in the coil will cause this to fail/misfire occasionally too.

but either way, its fixed :)