Possible Problems with HT leads on C240

[thomasbeeton]

Hi,

I've just changed the plugs in my '98 C240 and everything seemed OK on idle however when reving up to 4000 RMP it starts to misfire badly. Can anybody tell me if this is a lead problem. I've double checked all the connections they are secure. The plugs have a preset gap (Champions KC11PYP)
Is there an easy way to work out which lead or coil set is the problem?

Is there something else I've missed? With the old plugs idle was slightly rough but the plugs had done 68K


Thanks


Thomas

 

[MondeoMan]

I'd verify the plug gaps are correct as a first step.

 

[Bolide]

Plugs

I'd whip the new plugs out and gap them but, while they're out, I'd stick the old ones back in and give it a spin

If the car goes back to "normal" (ie as it was before the plug change) then the problems with the new plugs (in some way)

If it stays misfiring at 4k with the old plugs then maybe you disturbed something when swopping them over, or a lead has failed

Are you sure the new plugs are correct?? When you put an old and a new plug in your hand, side by side, are they the same?


Nick Froome
www.w124.co.uk

 

[robbo]

Just to clarify, when you rev up to 4000, are you doing this when stationary and in neutral? or is this when you are driving?

The engine has a rev limiter that cuts in when you rev above about 4000 rpm in neutral.

 

[thomasbeeton]

Thanks guys, I was reving in park so this may explain the limiter cutting in. The plugs are gapped to 1mm. Is this correct for a C240 engine?