What causes a misfire?

[J444HN P]

My coils were new last year and im about to replace the spark plugs tonight.

But i get a slight shudder through the car every 3 seconds or so and the exhaust pops every 3 seconds.

When i start the car, The revs are way below 500 for the first 3 seconds.

Anyone shed any light on what it could be? :S

 

[CuppyDean]

HT leads maybe

 

[J444HN P]

Dont think mine has HT leads pal, Should mention its a Megane Coupe with an F4R so the same idea.

My 'HT leads' look wired in as if they cant be changed.

Thanks for replying though!

 

[mat-nos]

missfire is caused by ignition/timing/fuel faults so plugs/leads is a good place to start. could be that your coil pack could be faulty again. then your starting looking along the lines of checking sensors/fuel pump/timing as it could have slipped....
the other option is to get it on a dianostic mechine so your not spending out on thinks that might not need changing....

 

[J444HN P]

Might do that as the EML came on recenlty but the misfire has been going for a few eeks now, just never bothered me enough.

 

[sideways danny]

i believe you will have pencil coils (1 coil on each spark plug). these are well known to be an issue in loads of renault engines

 

[J444HN P]

i believe you will have pencil coils (1 coil on each spark plug). these are well known to be an issue in loads of renault engines

Replaced them last year but may aswell buy another 4 for the sake of £40.