Misfire above 3k

Post Sat Jan 12, 2013 8:47 pm

As the title sugests my car has developed a misfire above 3000rpm, it ran fine before i parked up then 2 minutes later got back in and it ran like crap.
Ive tried a few things but i need ideas i'm dumbfounded by this, any help will be muchly appreciated!!

Post Sat Jan 12, 2013 9:49 pm

I'd be checking your ignition system over, especially the condition of your dizzy cap and rotor arm. Make sure everything is correctly plugged in.

Post Sun Jan 13, 2013 12:32 pm

I will be checking these during the week, i dont think its a lack of fuel as when i get to 3500rpm it starts popping banging and spitting flames. so im thinking ignition.

i swapped the cps and for the ones from my m20 that didnt change anything so can rule them out.

Post Sun Jan 13, 2013 4:39 pm

Sounds like your dizzy cap and rotor arm. I had this same problem when I got my 325i cab, ran fine but missed at high revs, popped like crazy.

I guess if the rotor and dizzy are faulty they can't arc accurately to the correct nodes at high revs.....

Post Sun Jan 13, 2013 7:05 pm

yeah i'll rip them off tomorrow after work to see if i can spot any problems an probably source new ones. i just cant understand how it ran perfectly fine then 2 minutes later this..

Post Sun Jan 13, 2013 7:27 pm

Could be just damp in the dizzy cap or leads

Post Sun Jan 13, 2013 7:35 pm

surely that woud have dried up by now its been like this since before christmas?

Post Sun Jan 13, 2013 7:56 pm

Check the resistance of your leads too, they should read about 5-6K ohm, the lead that goes to the coil should be 1-2K ohm.

Post Sun Jan 13, 2013 8:43 pm

good call i will try those too. thanks for the help guys i really do appreciate you help!

Post Tue Jan 15, 2013 4:52 pm

took the dizzy cap off last night to have a look seemed ok a tad dirty but ive seen alot worse.
went to take the rotor arm off, undid 2 of the allen bolts and it fell out....that would be my problem then! good news i had a spare basically new one from the old m20 engine so bunged that in and hey presto she runs happily to the limiter again!

Post Tue Jan 15, 2013 9:44 pm

Easy fix, good work Mike...!

Post Tue Jan 15, 2013 11:46 pm

other peoples cars i can give advice on but when it comes to mine my mind goes blank. i did the conversion myself with no help at all except looking things up on here and google. in my head it was a loose wire as it was a sudden change. oh well its fixed now and seems to rev better than ever, first time ive seen a broken rotor arm too!