Been a LOONNGGG time since I messed with a 1.8td but iirc Percybigun on the Mondeo forum is/was the oracle.

my 1.8td had a bleeder valve on it to raise the boost, i also had to tap off the boost hose before it went into the inlet mani for the boost gauge, I can’t remember why but I think it may have been to do with incorrect readings.

i used one of the roose motorsport tap off kits. I’d probably tap off a boost hose first, check if your still getting 5 psi then check for leaks by making a leak tester with some bungs and pumping air into the system, after all that I’d look at the actuator, but if your going to raise the boost you may get away with using the bleeder valve and then just keeping an eye on the boost levels with your gauge.