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.
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