[dcb]

I do not have the application knowledge you seek regarding coils, I would simply look for a large one, i.e. some hot rod kid parting something out. your metro has a pretty standard looking coil I assume.

the guess is the mileage is crappy when lean and loaded. so adding fuel pressure might help. It is a guess. A replacement regulator can be had for $30 or less. But the regulator determines the pressure, the injectors open up for X amount of time based on the assumed pressure.

It may be that the fuel pressure is low because of an old spring in some of your fleet too, dunno, measuring it and comparing to stock might be useful info. you need like a 70psi gauge.