C18 engine in D9T Dozer Fueling problem.
At low idle I get fuel pressure of about 410 PSI
At high idle(2000 RPM in N) it drops to about 350PSI and engine loses RPM sporadically.
At high idle under full load RPM maxes out at 1600RPM
-> Replaced filters : OK
-> Checked all fuel lines : OK
-> Checked for debris in all components a pressure regulating valves : OK
-> Replaced back end of mechanical fuel pump : Found slightly better results but still losing RPM sporadically as before.
-> Replaced all rubber seals while dissassembling.
I noticed an electrically controlled valve on the return side of the filter housing, could it cause this problem if it is faulty or not receiving signal?
I only replaced the back end of the mechanical fuel pump, could the gear side of it be damaged and if so would it cause the high idle RPM loss but not at low idle?
Is there anything in the fuel system I've overlooked?