My Mark 8 has a miss/stumble when I touch the gas. It happens at part throttle. I got a 542 code, can anyone give me some help on this. 95 Mark 8 LSC. Thanks

Code 542=fuel pump circuit open EEC processor to motor ground.

Could be a bad fuel pump or relay. You need to check your fuel pressure and go from there.

I just installed a new BBK 255 fuel pump two weeks ago. I will check my fuel pressure and adjust it according. I am also getting codes 538, 536 and 632 with the engine on. hmmmm.

This three codes show that you didn't do everything nececcery procedures during key-on-engine-running test (press/release brake pedal, cycle TCS, breafly press accelerator pedal). Reread the test instructions and perfom it correctly.
542 is not about the pump itself, it's about hi-speed fuel pump relay and wires around.

I will redo the proceedure. I went out and purchased a fuel pressure just to make sure that I have the correct fuel pressure. What is the correct fuel pressure? I have a adjustable fuel pressure regulator.

Fuel pressure, according to service manual, must be 30-45 psi engine running & 37-43 psi pump running, and the engine off.