Backpessure plays no role with the turbo cars. Ask any Turboford.org member about their 3" setups and lack of mufflers at all... even mine...hondahunter93 said:you need back pressure, get a muffler or glasspack on there
The Problem with the Ignition if you swapped out the TFI, Ignition Wires, Plugs, Cap and Rotor... could be the PIP in the dizzy, or even your fuel pressure... but give a rundown of all the equipment your car is running as all extas may play a big role in this as well.
Check your base Fuel Pressure... maybe your secondary fuel pump is shot. or maybe the wiring is bad... A have seen these problems arise on stock XR4's, T-Bird TC's and SVO's. But it could be as easy as Timing too.