I searched google for related problems, but haven't found any posted solutions. Lots of suggestions but none seemed to fix the problem. I have a '90 GT, with the laundry list of bolt-ons like most of us power hungry Mustang owners. I bit the bullet and bought a Kenne Bell Blowzilla with the standard inlet, and installed it this past April. I had some minor fitment issues, but it seemed to work out. With my 190lph fuel pump, 30lb injectors I had no detonation when flooring the accelerator. I bought an XCT chip and planned to dynotune when I had a chance, but there seemed to be no hurry (haha). I drove her maybe three times with the 3" pulley (8lbs boost) before changing to the 2 7/8" (10lbs). I took her out maybe twice with zero problems. The third time with the new pulley, she starts backfiring like a machine gun when around 1800 rpms...the rpm needle dipped to zero as she wanted to stall, but recovered several times before stalling altogether. The car restarted...but a few miles later, the same thing with with the backfiring, then she quit outright. Also, I noticed the brake pedal became increasingly harder and harder to depress. The booster is a new/rebuilt unit I put in when converting to a set of '98 Cobra brakes last year, using the '93 cobra booster and master cylinder. Towed her home, and replaced the distributor and all spark plug/coil wires. She started, and I set the timing to 0 degrees, since KB says to retard the timing 1 degree per pound of boost. Car started, but same thing...backfiring, no power until she dies again with no starting. Replaced the ignition module and hall effect sensor, and she started again, but again stalled around 1800 rpms, and won't start again. Brakes are still hard as a rock. I checked all the vacuum lines and they are intact. I suppose the booster not working could be coincidence, but it sure is strange. I checked and the #1 piston is at TDC when the distributor rotor says it should be, along with the crankshaft damper timing marks... As I said, I found several threads on several sites with similar issues, but no "Holy Crap That Fixed It!!" moments.