Chevrolet Repair: Service engine soon light is on, vacuum leak, oxygen sensor

Question
1990 silverado suburban 350 motor ..when light is on it will not go over 50mph. If you try to accelerate it will slow down rather than speed up. Getting a code 44 ,lean exhaust. No miss in engine, runs smooth otherwise. No repair history,just purchased. Runs good on flat surface or downhill, but no power on uphill. Has 180,000 miles on motor but sounds and ran perfect until a few days ago when the light came on. Sometimes the light will go off at a stop sign or at speeds below 30mph. Could this be EGR or Oxygen sensor? What is your opinion? Thanks           Ted Flamm

Answer
Hi Ted,
The EGR will usually make it run bad, like a big vacuum leak.
I believe the oxygen sensor is working properly.
I think it is a low fuel pressure problem. When you press the gas pedal, you allow more air in, but if there is no fuel injected to go with the additional air, it will actually slow down, and the exhaust will get very lean.
I would connect a pressure tester, but make sure it is connected where you can see it while running over 50.
It needs to maintain a good 13 PSI.
If lower, I would first suspect filter, which is under the cab, beneath the drivers seat, clamped to the frame.
If pressure stays low after replacing the filter, pinch the fuel return hose, and see if the pressure regulator might be sticking open.
If the pressure doesn't max out at about 14PSI with the hose pinched, there may be a hole in the hose INSIDE the tank that connects the pump to the fuel line.
Van