I've got an 87 TPI engine with fluctuating fuel pressure. It swings back and forth between 28 and 40 PSI while running. The car will barely start and has a hard time running. RPM has little effect as far as making it more or less stable. Is it the Fuel Pump or the Fuel pressure Regulator that's bad? The Fuel Filter is new.

 

clamp off the return fuel hose and prime the pump, it should hit about 75 psi, if it doesn't get close, its time to get a new one.

 

You can also test the fuel pressure regulator hoses and the regulator itself for vacuum leaks. I had a vacuum leak that leaked vacuum at first cool start (spiked pressure, causing rich, plus the vacuum leak itself), then sealed off better once the hoses got warm (normal vacuum = normal pressure, car ran fine).

 

Morley,
Is the return line the smaller of the two lines coming from the TPI and around the driverside?

 

May be the fuel pump.
We installed my Holley pump on my friends 86 Z today and with my pump on his car the fuel pressure doesn't jump around at all.
Sits nice and steady on 37psi at idle and 45psi when you rev it up.
With his old pumps on the car, the needle would bounce around all over the place. both of his pumps were dying, and one actually died on us yesterday while we were working on the car.
The other one quit today right after we put it on. So we pulled the Holley off of my T/A and put it on his Z.