misfire help please

[nathT5]

i,m still wanting a T5 but the one ive been after has now developed a misfire upto around 2k,
but after 2k it still runs sweet with no problems,
any ideas on this and are they prone to anything to cause this?

or is it the usual checks? plugs, leads, etc?

cheers...

[nobananas]

Do a stage 0 first, plugs, leads, dizzy cap, rotor arm, oil 'n' filter and check all vac and boost pipes for leaks then see how it's going.

[nathT5]

Do a stage 0 first, plugs, leads, dizzy cap, rotor arm, oil 'n' filter and check all vac and boost pipes for leaks then see how it's going.

cheers, would these things not cause it to miss all the time and not between tickover and 2k?

[nobananas]

cheers, would these things not cause it to miss all the time and not between tickover and 2k?

You'd think so, dodgy leads and plugs tend to cause misfires under load which then dissapear when cruising but duff dizzy caps and rotor arms can cause odd running all over the place. Had an odd one on a Renault 5 turbo that I swear felt like overboost as it only happened just as the boost peaked, turned out to be a cracked rotor arm. The cap and rotor arm often get overlooked as well and you may even find oil in the cap from a leaky cam seal.

[nobananas]

Ohh, just thought, might also be worth checking down the plug bores for oil contamination. Often the oil filler cap leaks into the valley under the plastic plug cover and starts filling the plug bores up, can also cause odd running problems as the plug lead and top of the spark plug is swimming in oil.

[nathT5]

cheers matey,
so your not thinking anything serious then???

[nobananas]

cheers matey,
so your not thinking anything serious then???

Probably not, it's always best to go through all the basic, usual stuff to rule it out before worrying about it being anything more serious. Our 850's are cracking on a bit now and a lot of the ones I've seen are still on their original cap and rotor arm and original leads, they don't last forever so best to change them if you're not sure when they were last done.

[nobananas]

...it might also be worth having a compression test done, (just to put your mind at rest !) as a burnt valve can cause similar problems ie low rpm misfire that appears to go away at higher rpm's.

[nathT5]

thanks for that nobananas,
think i,ll have it as its cheap enough and (hopefully) should,nt cost much to fix,

soon to be a T5 virgin..