i need help please

[timw]

I have a renault megane 8 valve 1.6 1998.
The problem started last week where after i went to drive away after getting home from work.
The car felt very lumpy, when i looked under the car, i noticed the CAT was bright/glowing red.
I have replaced the CAT and the Exhaust Manifold, from cold it started and went fine, yet went it was warm, i went to drive again, and the original fault was there as above.
I then thought it was the middle section of the exhaust blocked not letting the gasses out, thus the CAT was glowing again. I then separated the exhausts just to get home, but this did not work, as when i looked under at the CAT it was still glowing, and a blue flame was coming out of the back of the CAT pipe.
Does anyone have any ideas as to how fuel must be getting into the exhaust and buring in the CAT.
Your help is very much appreciated.
Regards

Tim

 

[Le Champ]

Your megane is 'lumpy' because a cylinder is misfiring. Each spark plug has an ignition coil unit above and one of these has failed (a common fault) causing misfire/lumpy running, consequently unburnt fuel is passing from this cylinder into exhaust system and burning in the cat. Replace faulty coil on offending spark plug/inspect each plug. You will soon notice which one is responsible. Older cars have one large ignition coil however, more modern cars often have one per cylinder. Also check gap/condition of plugs.