Misfire - any ideas??

Hi guys,

hoping some of you might be able to suggest some more checks I can to do to try and figure out whats causing the misfire I have on my car. Below around 2000 rpm the engine seems to misfire as though it’s only running on a couple of cylinders. The misfire is’nt happening all the time and I can’t seem to correlate it with engine temp or anything else. Once I get the revs above 2000 rpm it runs great.

I’ve checked out the TPS signal, balanced the throttle bodies and checked the leads, plugs, etc but can’t find anything amiss. I havn’t changed the mapping in the emerald either so can’t figure out whats changed.

Any clues as to what could be going on? Coil pack?



If those things dont work out, try making sure the throttle pot is correctly aligned and that the overrun fuel cut-off and idle control is set correctly.

It is worth attaching a laptop and going for a drive to repeat the problem with the M3D softare loaded and in the live adjustments page, make sure the passenger does the checking! if the fuelling is lean or the advance well off this might indicate a problem in the base map. The load and speed sites shown will give you an idea of where in the map to look and the Lambda feedback will help establish if the problem is ECU / Map related.

Misfires are notoriously difficult to track down, careful elimination of each component in the high tension system and fuel delivery can help to nail it. check all connectivity, injector loom, air and water temp senders as well.


The engine has ran faultless for the last year and I havn’t changed the mapping at all so I can’t understand why it would be map related. I’ve recalibrated the TPS and checked that the idle control valve is closing fully once the engine is warmed up.

Noticed using the logging function in the emerald software that the lambda value was dropping out randomly to around 0.3 so I thought the lambda sensor may have been duff. As a result I disabled the closed loop function but the problem remained.

I dont understand why it’s only happening below ~2000 rpm. and above that speed the engine runs great.

KingK - any chance of borrowing/buying that spare coil you have to check mine is OK?

Havn’t changed the plugs - but they look OK.



I had a misfire like this it turned out to be the vacuum pipes that fit onto the inlet manifold had started to leak, replaced them and it�s been fine since.
Not saying that�s what it will be but worth a look.

Good luck

Also, plugs that look good can be bad, even new can be bad.
I would change them as well (but I agree with above, check all the vaccuum hoses first)

Just to close this one out.

old coil and magnecors - missfire still present
old coil and standard leads - missfire still present
new coil and magnecors - improvement but still missfiring
new coil and standard leads - no missfire !!

So the new coil and reverting back to the standard leads has cured it. Never really been happy with the quality and fit of the magnecors - wondering now if they have managed to damage the coil??

Thanks for the help guys,


Nope, just shows you that what others consider an upgrade many times it’s not.
Magnecors seem to work for some people because of their higher conductivity, but electrically, the less losses are when the circuit’s impedances are matched and if Magnecors are much lower…

I say, there is nothing better than the standard leads 9well, except that they let water in )