Misfire
Author
Discussion

TorqueVR

Original Poster:

1,978 posts

229 months

Wednesday 29th August 2012
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My 400 has developed a misfire from about 4000rpm. Any ideas where to look, bearing in mind I'm not too good at mechanical stuff?

Dr Mike Oxgreen

4,466 posts

195 months

Thursday 30th August 2012
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Misfires at high revs are very often ignition related. My first bet would be the coil, which in normal operation has to "charge" and "discharge" hundreds of times a second. It has to work very hard indeed at high revs, so if the coil's getting weak the symptoms will show themselves at high revs.

Could also be the ignition amp module, which on later cars is right next to the coil.

But before replacing parts, check for loose HT leads first. Make sure they're all seated firmly at both the plug end and the distributor end. Don't forget the king lead between coil and distributor as well.

Also, try running the engine in the dark and look for any arcs - it could be that one of the HT leads is letting the spark find an easier path to earth.