I have a 93 gt that has a backfire issue. I did not have this issue until i disconnected the FMU that was not working properly. It will backfire if I let off the gas over 3k or if I shift over 4k. I have been working on cars for years but this is my first supercharged car. There is a Air/fuel gauge installed, which does show a slightly rich mixture when it backfires. I know this is not the most accurate meter because it is not a wide band. Any ideas? Fuel pressure is 38psi at idle.