The back fire on LPG is usually due to cross firing ignition lads, do you have spark and fuel pressure on the petrol side and injection pulse? Depending no the gas system used, it should start on petrol and switch to gas after a pre set warm up time, it will not start on LPG. Also, check for codes and make sure no other vacuum lines have blown off.
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Tuesday, November 7th, 2017 AT 2:58 AM