Low fuel pressure, lean condition left bank

[iheart2code]

I have a 1993 Ford Ranger 4.0L v6 2WD and I have been fighting a code 136, lean condition since I bought the truck.

I think I have traced the issue down to low fuel pressure coming into the rail. When I perform pressure tests, I see the following results:

- pressure at KOEO: 34 PSI (spec says 35-40)
- pressure at idle: 28 PSI (spec says 30-45)
- pressure at idle with vacuum hose disconnected: 36 PSI (spec says 35-50)
- pressure when goosing the throttle: jumps to 30, then settles to 22-24 PSI
- pressure 5 mins after engine off: 30 PSI (spec says 40-60)

I replaced the 12v battery, which was old and not supplying enough voltage. I tested the fuel pump relay and it's good. I have recently replaced the fuel pump and fuel filter. I have smoke tested the intake system and not found any air leaks between the MAF sensor and the block. I also replaced both oxygen sensors. I have replaced the fuel injectors with refurbished units. I tested the fuel pressure regulator and it's good.

I would like some help with where I should go next with diagnosing the problem. Thanks in advance.

 

[franklin2]

How did you test the fuel pressure regulator?

 

[iheart2code]

I removed the vacuum line while the engine was running. Fuel pressure jumped from 28 to 36.

 

[franklin2]

What if you left the vacuum line off the regulator? Would your lean codes go away? Just as an experiment. Of course plug the hole so it will not suck air with the line off.

 

[iheart2code]

I have left the vacuum line off the regulator and have the same result -- code 136 lean left side.

 

[franklin2]

I have left the vacuum line off the regulator and have the same result -- code 136 lean left side.

So maybe it's not a fuel delivery or pressure problem? I am assuming you erased the old codes before the test?

 

[iheart2code]

Yes, I erase old codes. These are engine running codes I am seeing during the self test.

Maybe I just have an air leak somewhere I can't easily see or hear. I wonder if there's a loose vacuum connection in the cabin somewhere.

 

[franklin2]

You would think with a general air leak, you would get lean errors on both sides? I wonder what would happen if you swapped O2 sensors side to side? I don't take that idea lightly, I know they can be hard to get out sometimes.

 

[iheart2code]

These are both new O2 sensors, and I have confirmed by back probing the wires that I have the right sensor data getting to the PCM.

 

[franklin2]

Leaking exhaust manifold gasket on that side? Cracked exhaust manifold on that side?