Light to medium throttle surging

[cobra30689]

I have a stock 4.8 in a Jeep YJ with a part throttle surge in closed loop that is giving me fits. No codes. No misfires under load on my Tech 2, only occasional ones at idle. 55psi running fuel pressure, drops to 52 under hard load. Brand new fuel pump, returnless fuel system with Corvette regulator. 2002 Silverado calibration with injector flow data changed to reflect the returnless setup from a 2004 4.8. No ignition issues that I can see, ACDelco #6 platinum plugs, new wires. I have a couple of ideas but none make sense. The surging started after replacing the fuel pump.....the original was failing and I retuned the engine to run at 43psi. Once I installed the new pump I reset the injector flow data and reset the LTFT's. Jeep runs like a scalded cat now at full throttle, so I really don't think it's a fuel issue. This makes me lean towards the MAF. Stock Delphi unit (found in a junkyard as my engine didn't come with one) of unknown origin. It IS a little closer to the throttle body than normal as there simply isn't enough room under the hood of a YJ. Should I attempt to recalibrate the MAF? Tune and log attached (excuse the bouncing VSS signal, I have a Dakota Digital inline cable VSS that is picking up noise from somewhere). Pic of intake tube for reference.

197812001_10225355674068652_2454062439434199596_n.jpg

[GHuggins]

Only looked at the pic under the hood, but try re-indexing the MAF. Put the connector in the upper rear corner as looking at it from the front of the vehicle. Both instances you're describing are low airflow and air will typically hug the inside edge. Good possibility the MAF just isn't picking it up. Worst case - run it in SD...

[ns158sl]

You never dialed in the MAF? I would get the fuel trims inline and see if you still have an issue.

[cobra30689]

Re-clocking the MAF yielded no change. Guess I'm going to have to try dialing it in. Frustrating because this wasn't an issue prior to changing the fuel pump, but at the time the engine wasn't running the way it should.

[gametech]

Keep in mind that even if you rescaled your IFR for 43psi, all the data in your offset vs volts vs vac table will also be just a tiny bit wrong, so you would need to retune anyway. If pressure differential did not matter to that table, then it would not change based on vacuum.