Hi guys, I have a vy berlina with an ecotec v6. Its missing on cylinder 4 and ive changed the plug and lead. There is plenty of spark. Its a factory duel fuel car. The thing i noticed with it is you remove the oil filler cap and it die down in the revs and very slugging or both fuels. Put it back on and it seems better but the limp is still there. there is a vacuum under the rocker cover and i know it points to valve stem seals but to make a cylinder dead it must be more than that?? Any ideas would help....