I have an 89 formula with a 350 tpi. I have noticed a lack of power and a lean condition. Turns out when I give the car throttle the fuel pressure drops. I replaced the fuel filter, cleaned the fuel rails, inspected the fuel injectors for junk, and just put in a high volume 255lph fuel pump, however the pressure drop remains. I can only assume that there is an abstruction in the fuel feed line somewhere between the gas tank and the fuel pressure regulator. There are no fuel leaks. Any advice would be helpful this is really started to **** me off. I thought about removing the feed line at the rail, remove the fuel filter and shoot air down from the fuel rail side to see if that removes anything. Anyone else have a way to clean lines or solve the problem? Could it be lack of voltage to my fuel pump? My battery shows 12.2 volts and the volt gauge with the car running is almost 14V.

 

A friend of mine had this problem right after installing a bigger intank pump. It turns out it was leaking fuel back into the tank because something at the pump wasn't sealed or installed just right.
I think some of the bigger pumps also require a better power source. My husband wired mine and said the factory wiring was a little too small for the pump, but mine isn't in the tank now.

 

my guess would be the regulator. It might be passing the regulator and returning back to the tank.

 

Evil 88IROCZ did you ever get this problem fixed? I'm having a problem with my fuel pressure drop but 10 when I'm at partial throttle. I did have the fuel pump replaced last year after my stock pump died on me. Now I have a 255lph in tank fuel pump. HELP!!

 

A quick check is to test pump output volume. A good pump/filter/regulator should flow at least a pint of fuel into an open container in no more than 15 seconds.

 

I should have stated this in my previous post but I just put a brand new regulator on the car yesterday. The all header tubes have been glowing red after the car runs for about 10-15mins. I took it to a shop to get the air/fuel checked and the shop said that I was 13 + over stock. The funny thing is I already had an adjustable regulator on the car..and it said I was running at 48fuel and the shop said I was at 58. I had the regulator changed and the fuel press was set at stock level (43.5). What happens is when the accelerater is pushed the pressure drops down to 35-38. The shop is telling me that either the fuel pump I have is too big..I'm running a Walbro 255lph or the fuel line is pinched on the return.