All Kinds Of Problesm!!!!

Slapping a 90mm meter in with 42 lb injectors and a stock computer is nowhere near a correct solution. Once you start getting over 30 lb/hr injectors sizes, the stock computer fuel and spark tables become a big issue. Even the injector break points for what the computer thinks are 19lb injectors are a night and day difference when comparing them to 42s. Now that you've got all that hard earned money spent on a meter and injectors that in combination with a stock tune don't like one another, you have a couple of options. One is to get custom dyno tune at a reputable shop. The initial tune with chip can cost as much as $600 while susbesquent tunes (now that you own the chip) can be around $100. The other option is to get an EEC tuner like the TwEECer. There is a steep learning curve involved with this kind of solution if you're not already well versed in Auto tuning. A TwEECer can be had for about $450 and an initial tune can cost another $200 or so if you have a shop in your area that knows the TwEECer. There are other EEC tuners out there aside from TwEECer to choose from and my mention of TwEECer is just used as an example. Another popular EEC tuner for Mustangs is the Anderson PMS. It's much simpler to use and configure but doesn't have the all inclusive control that the TwEECer does. You will also not be able to use the PMS to adjust your injector break points (which is pretty significant for properly dialing in idle and part power characteristics).

Take a look at the link below to get an overview and idea of what some of the other ECUs that are available. Be sure to also take a look at the forums for each one you research and get some idea of the benefits and quarks for them.

http://www.turbomustangs.com/techarticles/ECUarticle.php

Good Luck!

Yep... most here are well aware of Mike Murillo and what he's capable of. IMO, You would be in good hands. He'll definitely get it all straightened out for ya.