Help Narrow Down Issue

*Acknowledges the forbidden nature of New Account/Troubleshoot Help request thread. *​

With that out of the way, let me preface by saying: Yes, I have gone through the forums, checking for issues similar to mine. I already have a list of likely issues, and I am mostly wanting a “sanity check” so-to-speak to see if others point out obvious things I am missing.

Vehicle Info:
2011 Prius II, Approx 260K Miles, Southern California, Frequent hard up-hill freeway driving.
Average Maintenance Routine:
Oil 5K miles, Air Filter 20K miles. Traction Battery replacement 100K miles ago. Acc Battery replacement 20K miles ago. Major engine rebuild 30K miles ago (Coolant change, spark plug change, Head Gasket chant, injector cleaning/change, EGR valve/cooler cleaning, PCV change).

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Beginning at the start of summer, the average MPG loss thanks to AC running look my average 48 mpg down to 45-46, with steady decrease over course of 2 months, and an overall feeling of sluggishness. No improvement with oil change, use of high mileage Techron, air filter change, acc battery exchange. No CEL, no misfires. Confirmed sensors were active using OBD tool and old fashion pulling (undoing each injector and MAF, confirming the ECU immediately shut down engine and generated trouble codes)

Began using Hybrid Assist and Dr. Prius, confirmed battery health at higher than average for milage. Began recording STFT and LTFT data: STFT peak and dip before leveling to 0% as expected but appear to lag compared to recording others have made (taking on average 5-7 seconds to level out once engine RPM has stabilized). LTFT initially reported consistent lean of 4%-12% when idling, spiking nearly to 20% under acceleration at +85% load. LTFT have continued to steadily rise over the course of summer and fall, now sitting at 23% idle, with STFTs “bouncing” more often like ECU is trying to adjust.

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Finally generated first CEL with code p0171 while driving uphill on freeway. All freezeframe data appears “normal” or as expected for a lean condition, save for EGR% at 65% (will include photos of freeze frame data below). Did a “cheap vacuum leak check” (can of spray carb cleaner), found no notable change in RPM despite near saturating of all connections between MAF and throttle body, around intake manifold, spark plugs, EGR valve/cooler/pipe, PCV valve. Confirmed RPM would surge when cleaner was directly sprayed into air intake. Disassembled ERG valve and performed cleaning in case plunger rod/spring was sticking, found expected carbon build up but no where near complete blockage (approx. less than 1mm around walls of EGR connection pipe). No improvement after cleaning, reassembly, and second vacuum leak check. Current LTFT 23%, STFT still “jumpy.”


I suspect a failing fuel pump/clogged fuel filter/clogged regulator, as all parts are original and the tar glue around the pump cover appears intact with no evidence of scrapping. However, before doing a fuel pressure test, and replacing the entire assembly unit, I want to make sure I am not overlooking anything besides the usual suspects: O2 Sensors, MAF sensor, EGR, Injectors, Vacuum leaks, etc. Essentially “check my homework” please.

*CEL freezeframes:

 

Unrelated/"Horse Sense": Significant difference between MPG estimate from ECU and IRL estimates. Before the summer, the ECU estimated was on average 48-49mpg, with IRL values (literally divide trip miles by at pump amount) usually being 1-1.5 lower (as to be expected). As of the last refill, the ECU estimate is 42mpg, with IRL 49mpg. The prius ECU is well known for not having accurate estimates, so it's likely a coincidence, but it is interesting that [42\49]=approx 86%, while the LTFT shifts between 15% and 22% when cruising at around . Almost as if the ECU believes it's adding more (thus recording) more fuel, while it's IRL fuel consumption implies it's simply adding "enough."