Misfire

allbeast

New Member
Please help!
I've developed a misfire around 5000rpm. Changed the plugs 2000 miles ago and need advice on what plugs to put in and also what the gap should be.

Any advice on heat rating?

Dave
 

grim_d

Member
Not knowing what mods you have...

Ngk bcr8es@0.7mm seems to be the plug of choice up to so much power. (400bhp ish?) they are super cheap. Under £10 for 4.

For your misfire you should look at ignition components, I would start with leads then dizzy cap/rotor arm.
 

PobodY

Moderators
Staff member
I also run BCR8ES at around 0.8mm. - Go much wider than that and the problem might be spark blow-out unless you've got a stronger coil or you don't run much boost.

There's a bit of a balancing act; the smaller the gap, the easier it is to make a spark jump it (so it has less energy). The larger the gap, the stronger the spark... but when you add boost (and cylinder compression) on top it's like multiplying the gap.

Check for fault codes too; any chance it's actually an ignition cut because the car is going into limp mode?
 

Fast Guy

Moderators
Staff member
Another thing Ed pointed out to me is the build up on the distributer cap contacts. It gets a layer of oxidation? build up on them. (whitish powder) I don't know if you can just clean this off and reuse or whether you need a new cap.

Also, air leaks can cause misfires, could be worth checking all your hoses, big and small.
 

PobodY

Moderators
Staff member
You can just clean that off. - I've got a little file for just that job; obviously you take the surface layer off each time you clean them up, so it will eventually need to be replaced.

It's the same with plugs really; they're cheap and it's easier to replace them, but it wasn't that long ago that you'd clean them up, regap them, and put them back in.
 
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