well you need`d a fuel pressure gauge anyhow
l agree that it sounds electrial in nature. lf my car was doing that l`d be paying attention to Exactly when it happens:warm? cold? bumps? etc. Get out the multimeter and start checking from the battery outwards,you`re checking resistance values and continuity. lf you installed the systems in your car l`m sure you`ll find the problem.The first thing a Porsche tech would say is"check the relay under the drivers seat" ,on the 3.2`s that was the most common failure that fits your cars` symptoms..
PS_pics of the car?