Re: lpg backfiring
Hmm, when my LPG was backfiring, it was blowing the airbox off.. I spent a LOT of money at a garage where the people had no real clue. If I could do it all again, I'd just get a different converter, because it was to do with leaning out (probably your problem too), and the current converter on mine is too small anyway (probably the same for you).
On mine, they replaced the MAP, Oxy, LPG computer, tried using an "econovalve" (uses the manifold vacuum to determine gas flow), and in the end, got it running alright (it is now fine, leans out above 3500rpm, but doesn't backfire)... but that was about $1000 I could have spent much better :(
TQE, SWB, ATPS, Worst of the E-series.. and I wouldn't have it any other way