Recently bought a 2000 4.0 ranger with 194k miles on it. Previous owner said engine is completely rebuilt and machined, everything is pretty much new except for the drive train and suspension components. 1k miles after buying it the truck started running funny, very rough idle and hesitation during acceleration. I ignored it until it started throwing codes, at first it threw two codes, running rich in bank 1 and 2. I replaced the fuel filter, cleaned the tank (was very dirty), and cleaned the pump sock. After assembling everything it now takes a lot more cranks to start and just recently threw a code saying the fuel circuit relay was high and it’s running lean in bank 1 and 2. Can’t seem to figure it out. Any ideas would be more than helpful.

 

Neither can we until you give us the actual codes P0xxx.

 

Welcome to the forum

Yes, if possible post the codes, there are basic "lean codes" and more advanced FORD "lean codes"

Partial code list here: https://www.therangerstation.com/tec...trouble_codes/

FP Relay code could just be because you unplugged the FP relay or FP Fuse