Hi I have a 2003 mk1 RS focus with new leads coil pack plugs and it's got a misfire only in 5th gear and only under load and on boost and only when it's warm any ideas please ?

 

What plugs, plug gaps, boost? When did it start?

 

Plugs were recommended ford ones as were leads ( I did have ggr leads but went with original ford leads) plug gap were not checked from new and as for boost its on full boost when misfire occurs but as I said only when warm hope this helps as new to mk1 scene

Ps misfire was picked up when it went for tuning

 

Check plugs are gapped to 0.7mm. Then take it back to the place that tuned it. If it didn't do it before tell them that. What did the lads say on RSOC?

 

2 people have commented and said plug gap and one way valve air leaked but all pipes have been checked and plugs were gapped properly tuner thinks it's fuel related not fuel cut more like pressure been told to check fuel filter now and a full tank of fuel to see it that has any effect but any other thought or ideas are still welcome

 

The fact it happens under load could be either ignition or fuel.

If it's the latter you need to be careful, as you will end up with a meltdown, thus I would recommend you get it setup, part of which will confirm your AFR.

I don't think misfiring is particularly a problem on your car, this is what we suffer with, i.e. Cosworth owners due to the old ignition system, with WS (i.e. what you have) it provides a stronger spark and less voltage loss etc, the exception being if something is in a poor state, but you say you have replaced such components.

Martin