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 knoticed with it is you remove the oil filler cap and it die down n the revs and very slugging or both fuels. Put it back on and it seems better but the limp is still there. Any ideas would help....