1996 jimmy miss firing and back firing

[Gearhead Cowboy]

I have been working on my daughter's 1996 jimmy because of random miss firing. Replaced o2 sensors, cam sensor, cap and rotor, when I was home at Thanksgiving it was dumping raw fuel into 5 and 6 cylinders so I pulled the plenum and found melted lines going to injectors replaced csfi with the up graded mpfi and still have the miss fire. I am old school if I had this trouble on a regular distributor and fuel injection I can figure it out but this thing is getting expensive and driving me crazy. What am I missing? Any help would be GREATLY appreciated!!!!!

 

[pmuns]

maybe try

Have you changed the spark plugs they could be fouled by the raw gas. you might look at the plug wires when it is dark out. park where there is no street lights or other light source .Pull the hood and look at the plug wires to make sure they are not arching onto something under the hood .If they are replace them.