Quote Originally Posted by agrazela View Post
Yes, the FP on my topswapped 98 LeSabre just got weaker and weaker, instead of dying all at once. And it did just what yours is doing: cause massive KR when I punched it and max the IPW's because it was trying to pump fuel but couldn't because the pressure was tapering off at high load.

Fuel pressure values at idle were just at the low end of spec, but one tell was that the FP after keyoff would continue to drop gradually over time instead of settling down and holding. (Kind of like it sounds yours is doing.)

I went through all the same diagnostics, checking all the lines for leaks, replaced the FPR, etc. Ultimately, I replaced the pump (in my case with a TRE-340), and all my fueling problems went away.

I suspect the checkvalve / backflap (or whatever the heck it's officially called) in the pump went bad / stopped sealing well. The pump could flow, but it just wouldn't get up to or hold high pressure.

Good post! So it is a possibilty, interesting. For my leak down test, how long did you do yours for? I think i'll perform the same test on mine too. Let me know...