frog

Sorry for the lenghty post, hopefully this will answer most questions...

My cos 4x4 is misfiring under load (above 3k on wide open throttle), drive perfectly ok up to that, and even revs up if I feather the throttle.

I have cleaned all the connectors I can reach, the gap between the crank sensor and the pulley is .4mm, which I believe is ok.

Now, I have had a play with the plug gap, .7mm and I get loads of mis-fire (even below 3k), .6mm is better but still not quite right, .5mm is loads better but still I get the occasional mis-fire and hesitancy.

When I come back from a short drive, the plugs look dark which suggests that there is a weak spark (?).
Plugs 1 and 4 were more sooty than 2 and 3, so swapped them round (1 and 2, 3 and 4). Just been out for a drive and 1 looks more sooty than 2 again.

Now, is it safe to gap lower than .5mm ? Is this just hiding a weak feed the the plugs ? I don't believe the HT leads and coil have been replaced for years now .

Am I on the right track or completely off my rails ???

Thanks in advance.

frog

Forgot to say that I also have put a completely refurbished head (new valves, guides and seals) which could have increased compression slightly resulting in a blown off spark if it was weak already.

SPADGE

.4mm is too small a gap for the crank sensor i believe! I think it is supposed to be nearer .8mm
Doubt this is the cause of your problem which could be leads,coil etc etc...

frog

Cheers Spadge,
I'll check the crank sensor again and look it up in the manual.
I have just ordered as new set of leads and a coil.

Greg

gurnE

Crank sensor is 0.8-1.0mm as Spadge says

Deffo sounds like you have some ignition issue, you should not have to gap plugs as low as 0.5mm

frog

Thanks guys, gotta wait for the bits to arrive now and re-gap the crank sensor.

Could a head rebuild increase compression enough to cause blown out spark ? I think I might have been border line before and the extra compression just is too much.

Does that make some kind of sense ?

Guinnless

Extra compression from a head rebuild won't cause any problems. More likely it's the leads.

frog

Cheers Guinnless, hopefully that's all it it m8.

wimwerf

i also had mifires a lot......but for me a group a coil solved it. (with new plugs off course).

frog

Grp A coil is what's on order

wimwerf

cheers

CosRush

Froq,

Keep us posted on the outcome.

I have a similar problem and have yet to find the problem.

I'd be interested to know if you cure yours...and if so how....

frog

Will do m8, received coil and leads yesterday, should be fitting them tonite.

frog

Coil and leads replaced, plugs gapped at 6.5mm, still had a slight misfire on boost at high revs (4500 odd).
Thought, oh well, I'll just re-gap at 6mm and see how it goes, then this happened !!!

https://passionford.com/forum/viewtopic.php?t=71820



I guess I won't know what the misfire problem was for a while now.