420A fuel problem (code 51)

[titogs95]

Recently I swap a 420A engine (97) into my 95 eclipse.
Everything bolts on with out problem, with an exception of the fuel rail. (Because the 95 has the FPR in the rail and the other one doesn't) so I put my old Fuel rail on it (95). It was working fine until a few hours later (40 miles later). An engine code shows up.
The code 51. By, what I read that means I am running lean.(am I right?)

So I am running out of possibilities.
Is the fuel pump?
The injectors of the 95 are different flow than the 97?
Dirty injectors?
I should not put the 95 fuel rail with the FPR? (Should I put back the 97 one?)
Do I need the FPR, on the system?

I hope u guys can give me a hand on this!

Thanks in advance.

Tito

 

[titogs95]

BTW this problem on my car got fixed by remplacing the O2 sensor.
Stupid O2 sensor!!