fuel pressure issue

I'm still trying to run down the miss and I think I'm there now. No vacuum leak and electrical is good. Fuel pressure regulator was bad, stock unit was 50psi. I replaced it and got the pressure back to 39psi. Still have the bad miss. Did the fuel check again and driving down the road the fuel pressure was at 32psi. Under boost it dropped to 20 psi and stumbled terrible. I replaced the fuel pump about 6 months ago with a new Walbo 255. Is it a bad pump again? This is a 87 TC. What is the other thing on the other fuel railfrom the regulator.

Not saying this is your problem, but about 8 or 9 years ago, I experienced the same pressure drop under boost with a 2 or so year old Walbro 255. Pulled the tank and found the filter sock completely (and I mean completely!) full of rust. The solution was a new tank. You could also have a small split in the hose from the tank to the tank flange dumping fuel back into the tank or a loose clamp on that hose. BTW, I am assuming the fuel filter isnt plugged.

If you mean the circular "thing" at the back end of the rail, thats the pulse damper, which is basically a small accumulator.

Dropped the tank and pulled the fuel pump . The fuel sock was fine. I pulled off the fuel sock anyway and discovered the problem. In the bottom of the fuel pump There is a screen that looks like the one in a washing machine water line. It was full of black grit . I will get back together and hopely this is the problem. I didn't see any trash in the tank.

Glad you found the problem!