I picked up a small black box which has an on/off switch and 6 position rotary switch. There are two wires coming out of it, one for ground, the other to connect to what appears to be the C wire of the ICP sensor. The instructions say the blue wire with stripe, or if you unplug it there will be two wires side by side and one under them and that's the one to attach to. On my 97, its an orange wire with stripe. The box is sealed, so I can't get into it easily to investigate. Anyway, the claim is that by rotating the switch clockwise it will increase the injector pressure and it can be added on top of any chip or tuner already installed. It just increases the pressure on top of what's already tuned.
The wire to be attached to on the ICP is not spliced, just connected to.

Does anyone know of such a way to increase the injector pressure?

 

Icp mod is a waste of time. Will do nothing with a chip in. Very little without one.

 

Old school mod, I hope you didn't pay much for it.
Custom tuning on a TS 6 position chip will get you what you need correctly instead of trying to trick the ICP sensor.