Occasional Misfire - Any Suggestions?

[G15SEE]

Hi All

A few months ago I bought a 2005 1.6VTI megane saloon. Two owners from new and a FSH confirming mileage of just 26,000 from new.

As it was sourced from a trade outlet and needed a service the car received a major service including cambelt change. It also required a replacement spring on the rear, new pads front and back and a few other minor items fixed. In total the repairs amounted to over £800.

Before it was serviced it suffered from an occasional misfire - but only on a trailing throttle. As an example, if coming into a roundabout off the accelerator, occasionally after changing down a gear and reapplying the throttle the car would stutter a couple of times before picking up. In addition occasionally it was hesitant while pulling away and need a few extra revs!

If the car is driven slightly harder with a few more revs ( perhaps 4000rpm through the gears) there is hardly ever a misfire or any hesitation; equally so if the engine is revved slightly when changing down after driving on a trailing throttle, again there is usually no problem.

The garage has checked the car three times and no fault code comes up!

Any suggestions or advice would be greatly appreciated.

[chewbacker]

sounds like a coil breaking down slowly. remember that the lower the revs when accelerating the higher the load and strain placed on the engine and any poorly performing parts suffer most.
as under that condition the engine is working hard a weak spark on one cyclinder will be easy to spot.

think of it this way.
ask a kid to start spinning a playground round about full of adults the kid will struggle (weak spark under load)
if a adult starts spinning it for the kid the kid can easily keep it spinning on there own (weak spark no load)

hope that makes sense

don't accept the answer they work or they don't as i work in the motor trade and have seen this.

[G15SEE]

Thanks for that you were absolutely right. I bought a coil and randomly selected a cylinder. After I changed the first on the left there was no change; but when I swapped it with the coil on number three cylinder it was fine. Total cost £17.32 including P&P.