I have a holley 670 tbi part 502-6 and a wallbro 195 pump that is about 2.5 years old i changed the fuel regulator diaphragm and even with the screw bottomed out it will not go over 15 psi and under load it dips to 11 psi i am looking for about 18 psi and holding. I have no clue where to go now. if i had the stock pump I know that i would need a new one but I am running a good pump unless it has started to fail.

 

Bottoming out the screw will close off teh return passage, which should cause teh fuel pressure to soar to around 90 PSI. It sounds like the pump may be bad or there may be a leak in the tank on the supply side. As a test, get a set of hose pliers and slowly close off the return line. If teh pressure does not rise (dont let it go higher then 40 PSI), then there is an issue. Also, the stock replacement holley TBIs only could support up to around 15 PSI. Youll need a stronger spring to go higher.

 

well i have no leaks and i pulled the pump to check inside the tank and its ok so you think my pump is shot. can I use a tpi pump as a replacement

 

If it cant make over 15 PSI with the return blocked then its likely hosed. The TPI pump will also work fine so long as your not getting too crazy with the demand. With the stock holley injectors, though, you should be fine.