What are the main causes of a mis-fire

[zippee]

My Chim has developed a mis-fire at 2600-2800 RPM, causing a sudden loss of power at this point before once again picking up.
I'm running magnecor leads, stepper motor is clean and the coil is only a year or so old.
This in mind what else is likely to cause it? Is it worth changing the dizzy cap and rotor arm? If so does anyone know part numbers or donor vehicles so I don't have to pay over-inflated dealer prices for these parts.

[big_treacle]

When I had a missfire I just took it straight down the TVR garage. One of their mechanics listened under the bonnet and figured out what was wrong pretty much there & then (knackered HT lead). Fixed and happy in 10 minutes for a couple of quid.
I find on mine that occasionally the HT leads slip a bit from the part that goes on the plug (dunno what you call it) which is enough to make them spark on to the manifold & hence missfire.
Good luck anyway, it sucks when they don't work right.

[jem]

did I see someone here suggesting shorting leads as the most common cause of misfiring?

J

[MajorClanger]

zippee said:

My Chim has developed a mis-fire at 2600-2800 RPM, causing a sudden loss of power at this point before once again picking up. I'm running magnecor leads, stepper motor is clean and the coil is only a year or so old. This in mind what else is likely to cause it? Is it worth changing the dizzy cap and rotor arm? If so does anyone know part numbers or donor vehicles so I don't have to pay over-inflated dealer prices for these parts.

Could be a number of things. Check out This Thread with link for hire of error code reader.

There was another discussion recently, where someone had a misfire and turned out to be a loose nipple/connector on the top of one of the spark plugs (i.e. the bit that screws to the top of the SP which the lead clicks on to). Presume you've checked all connections, leads etc? I had a misfire, had checked leads were connected but found out it was a broken lead, only apparent on close inspection. Presume also, since you're using Magnecor leads, that these are fairly new?

Anyway... hope you get some better advice and solve the problem.

MC

[philr]

I had similar problems a while back, mainly when the engine was warm. This was shortly after fitting a set of Magnicore leads.
It turned out that the HT lead was arcing off to the header tank. A replacement HT lead solved this problem.

Hopefully its something as simple as this in your case as well.

[Podie]

Check the resistance of the Magnecore leads. If you have some OEM ones, refit them and see if it cures the problem.

[zippee]

Thanks for all your replies guys, I'll take a look at all your suggestions in turn tomorrow and see if any help.
Phil, the problem has seemed to occur since fitting the magnecors so I'll have a close look in a dark garage to see if I can spot any arcing.
I think I may also replace the dizzy and rotor as a precautionary measure - can't hurt since the leads, plugs, coil etc are all new.

[Steve_T]

Other possible is your Spark Amplifier. Not sure if there is a graceful degradation from these when they start to break down though.

Steve.

[chimburt]

if the problem occured after fitting the leads, i think maybe you have the answer.....?

[MajorClanger]

zippee said:

Thanks for all your replies guys, I'll take a look at all your suggestions in turn tomorrow and see if any help. Phil, the problem has seemed to occur since fitting the magnecors so I'll have a close look in a dark garage to see if I can spot any arcing. I think I may also replace the dizzy and rotor as a precautionary measure - can't hurt since the leads, plugs, coil etc are all new.

Any joy zippee?

MC

[zippee]

Not yet, I was busy the whole weekend struggling with my pads and discs which I changed. Never have I encountered such siezed components in my life.
I'm going to try and have a good look tonight.