The V8 Owners Forum -

got a 3.9 rv8 cross bolt block in lr discovery auto, standard hot wire lucas efi but with lpg and flame thrower coil/magnacor leads, k and n filter, running at about 8-9 deg btdc on the timing.
intermittant bad miss under load, but ok on tick over, while looking under the bonnet yesterday a huge tongue of flame/spark? flew out from under the dizzy, did it twice each time the engine ran rough but couldn't get it to do it again after i got me mirror on the stick out to see whare it came from.

i'm guessing when driving under load this is the cause of the miss.
thoughts are either flame front blowing out from the hole in the bottom of the dizzy,where you can see the bob weights spinning, could a firing in the sump find its way out from here via the front timing cover?
or a flame front blowing out from the head gasket on number 1 cylinder( seemed to come out at wrong angle for this though), or a bad short earthing near the base of the dizzy?
anyone else had this?
running on lpg or petrol makes no difference.

It sounds like you have severe blow by on the rings but I have never heard of it igniting the sump!
Mike

yep weird one, deffo looked more like flame than spark, i'm not getting any crank pressure issues/oil leaks and it comes and goes, you can feel the extra pot/pots kicking in or cutting out.
last time i had a detonation in the sump was a knackered old meastro van and it shot the dipstick out like a javelin, then the whole lot disappeared in oil smoke, just as i was looking under the bonnet, talk about brown trousers!
compression test over the weekend i think.
replaced all plugs last week(ngk bpr6es) in case they were sooted up(they weren't) exept no 1, siezed solid and could only just move it with 1/2 inch ratchet, so as going away with the caravan over the weekend bottled out and left it, dont want any snappy snappy swear swear!
going to off road do weekend after next so that one may have to wait a bit before i risk butchery.
its certainly not an old worn nail of an engine, fitted new at main dealer by the previous owner 30,000 miles ago.

Sounds more like something iffy in the distributor to me - have you tried a different distributor cap / rotor arm?

Chris.