1993 Mustang GT (see signature for mods) My GT was dynotuned 2 days ago. The tuner could not complete the tune because the fuel kept cutting out at 4000+ rpm. Engine needs more volume. At the suggestion of the tuner & the advice of others, i've upgraded the fuel injectors to 60lbs, upgraded my fuel pump to an Aeromotive 340, upgraded the fuel rails to a BBRC kit and upgraded the fuel lines to 3/8' inch. The upgrades were ineffective... In fact, the engine was running a little leaner than before. All other parts appear to be working correctly. The installation of the upgrades were checked- OK. Lines and hoses- OK. Engine making excellent power but when past 4000rpm, fuel cuts out. Tuner said that he opened everything up and the fuel injectors are working at 100% when the fuel cuts out. Checked ignition module- OK. Voltage is OK- new Optima battery. Tuner offered that the 60lb fuel injectors may not be what they appear to be since the fuel keeps cutting out. I disagree because with the 42lb injectors i had before, the engine was behaving the same way. I am thinking that if all is working as should be, the computer (A9L) might be the cause of this behavior. The tuner does not think so... Whatever the case may be, something is causing the fuel to be cut thus robbing me of lots of power at above 4000rpm. Has anyone experience this kind of behavior? Thank you.