intermittent missfire

[adrianl]

Have a 1971 240Z, goes well generally , but I seem to get and intermittent missfire occasionally. Shows up more when motorway driving, seems to happen every 3-5 minutes or so. Engine misses a beat, and then returns to normal.

Have checked plugs, has new plug leads, points and distributor cap all relatively new. Not a big problem but a bit disconcerting.

Anybody got any ideas on how I can track this down.

Thanks
Adrian

 

[DJZ 60]

Hi, I,ve had a simular occurence. this may be due to a fault on the distributer itself. I had a electronic tune up and you could see the sparks behaving erratically on the screen on one cylinder. I,m not certain if this is the case on yours. regards BAROT....Leic.

 

[240z]

I also had a similar problem with my old higher compression L28, which occasionally had a missfire at higher revs, or under load. It turned out to be the plug gap, which I gapped down to recommended (sorry can't remember what it is) and then it went away..

Could have just been an issue with my engine running slightly higher compression, however

 

[Nigel Brook]

Could be the coil breaking down or the advance mechanism sticking. Take the distributor cap off, suck hard on the tube leading to the distributor and see if the advance plate moves smoothly and snaps back again when you release the suction.

 

[zfarm]

If none of the above work ( and it could be any of them ), try replacing the Condenser - on the side of the Distributor.
Little Bastards they are, cost almost nothing, last either 10 minutes or several years, but you never can tell.

If the problem persists, then off to the Rolling Road you go...

 

[pmac]

And fit a proper Nissan condenser (like you have done with your points I hope), not the generic crap sold in the Motor shops etc.

 

[Rob Gaskin]

Just a thought have you considered a fuel related problem. If it is occuring during motorway driving it may be fuel starvation, either from insufficient pump flow or tank breather problems. Is your tank breather ok, they can leak fuel and it may have been blocked off at some time to prevent this. Also is the fuel line clear e.g. not blocked or crushed?

 

[adrianl]

Thanks for all the replies. I'll work my way through and let you know the result.

Adrian