I read your problem is the check engine light on and if so is there any codes on computer as for checking the Nikki converter there is a nut on the top of the converter it has a Phillips screwdriver slot in the center this is were you check the pressure. make sure you turn lpg tank off and start truck let it run out of gas before you open test plug also becareful there is a small o ring on test plug do not loose it or it will leak propane when you install back in converter as for pressure you should see around 4to 5 psi when truck is running could see a little more with key on not running should not drop when running steady at 5 psi hope this helps