91 Sidekick No start

[fixkick]

91 Sidekick 8v wont start unless fuel return line disconnected from FPR (not vacuum but return) then starts and runs fine. once reconnected no start

the return line is clogged and or FPR is bad.

when you remove any return line , nothing happens odd and is NORMAL, for sure.
now the worse case.
cars old have this bad habit of 2 things wrong at once,  for sure 30 years old
the cause can only be  proved with a fuel pressure gauge.

case in point,  a 1/2 clogged injector (or ECU running it way lean, inputs to ecu dead wrong etc. ) failure 1
then the FPR return line is clogged, causing crazy high fuel pressure the injector loves now that  it is clogged.
but yours is opposite,  it likes FPR line removed. doing that should do nothing but does, so the lower pressure cause engine fuel mix to be more correct.
3 things wrong? is possible.

Id use a fuel pressure gauge, to see if the pressure is in spec, hose on and off. (return hose)
that is what I'd do , so we can work from baseline of facts on that.
34 to 41 psi is spec, key on  3 seconds. or idle. or WOT or any time, it is stuck solid in this range and changes only with ALTITUDe.
good luck... finding all things wrong easy.