Ignition - to much spark?

I have a 99 Ranger 3.0 - with syptoms of a serious miss. - I changed plugs, wires and everything else in a tune up. Heres what's weird - the plugs seem to fire normally - as I'm used to on v8's - but then, some of them seem to double or triple fire at random. this is a first for me I'm used to a miss - not to double up. - This engine is a duel fuel and I'm told it fires a second spark on the exaust stroke (I can only guess emissions purposes). So is the double firing normal (which I'm guessing yes) and the other cylinders aren't keeping up or am I wrong? --- Either way Please, Please help - no check engine light - Please - my parents car before I start trhowing parts at it -Thanx all