4400 combine lacking power

Hi guys. I have a 4400 diesel John Deere combine that is
really lacking power. I have changed the fuel filter cleaned
the sediment bulb screen, pulled the return line elbow and
blew it out, I even opened the timing cover on the pump, I
also blew air back in the fuel tank at the sediment bulb. I
have full fuel at the sediment bulb. I unhooked the supply
line to the injection pump , then turned the key on and it
seems like an ok amount Hi guys. I have a 4400 John Deere
combine that is really lacking power. I have changed the
fuel filter cleaned the sediment bulb screen, pulled the
return line elbow and blew it out, I even opened the timing
cover on the pump, I also blew air back in the fuel tank at
the sediment bulb. I have full fuel at the sediment bulb. I
unhooked the supply line to the injection pump , then turned
the key on and it seems like an ok amount of fuel. Should
that be a really heavy flow of fuel with the engine off but the
key on? Could it be the fuel pump? Where is the fuel pump?
Im getting pretty frustrated. The engine runs smooth and
no black smoke. As soon as I start running corn through it,
even in 1st gear all the way slowed down on the variable
speed, it can barely keep it to 2,500 rpms. Its like a dog
and doesnt hold at wide open. Do you have any advice? I
appreciate any help you can give. of fuel. Should that be a
really heavy flow of fuel with the engine off but the key on?
Could it be the fuel pump? Where is the fuel pump? Im
getting pretty frustrated. The engine runs smooth and no
black smoke. As soon as I start running corn through it,
even in 1st gear all the way slowed down on the variable
speed, it can barely keep it to 2,500 rpms. Its like a dog
and doesnt hold at wide open. Do you have any advice? I
appreciate any help you can give.

Fuel cap vent? Besides the engine fuel filter my 2144 had a filter on the tank. Don't know about a 4400.

Engine air filter; could it need cleaning or replaced??

I happened to just replace the air filter. Is it possible that it is bad?

Couple more thought; did injector pump timing to engine change?? May check... How long has it been that the engine intake and exhaust valve clearance been checked??

have you pulled the sedmit bowl assy off the fuel tank to make sure it isn't plugged up in the pipe that goes into the tank

break fuel line loose at each injector, if the engine changes sound its good but if no change you have a bad injector causing loss of power. If the air filter was the problem you would have excess black smoke.

Bad air filter, as in restricted air flow to a diesel usually makes it smoke. I looked up the gallons per hour used by a 359 in a 2940 under full load was shown as 5.1. A pint of fuel every minute and a half gives you 5 gph. Just to maintain machine speed when entering the crop you are maybe at half load.

Make sure thefuel return line is not restricted as well.

What happens if you let the engine go down to 2000? Do you have full torque? Or what happens if you climb a big hill in road gear?

If your engine loose too much rpm but has full power, the givernor sprong is suspicious.

If your engine has full power on the road, but none harvesting, you have separator issues. I heard one rime a guy putting a new motor on his MF 9560, before realizing that the rotor was full of barb wire....