From the fuel pressure readings you have listed, your fuel pressure is too low. It should be about 35 psi at idle. 28 is too low and it can cause misfire and lack of power under load. Since you already replaced the fuel filter, your fuel pump will need to be replaced. The 4.6L engine in your Mark VIII requires the proper fuel pressure to give you the performance it was designed for.
I would like to see if you have any further areas I should look. I changed my fuel pump and fuel filter. I still have the same readings.
If I remove the vaccum line from my fuel pressure regulator I start receieving about 40psi at idle. When I replace the vaccum line the pressure returns to 28psi?
Please let me know of what I should check next.
Thank will try tomorrow
Ok I changed the fuel presure regulator and there is no change. Fuel pressure at idle remains at 28 PSI.
Could clogged catalytic converotrs cause something like this?