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2010 Lincoln Navigator 5.4L Fuel Trim Codes P0172 & P0175: Cold Start Issues After Fuel Pump Replacement

Model: 2010 Lincoln Navigator Fault Code: P0172 Posted: 2016-12-17 13:31

My 2010 Lincoln Navigator with a 5.4L V8 engine recently had the fuel pump replaced. Since then, it has developed difficulty starting when cold and now logs persistent DTCs P0172 (Fuel Trim 2 - Too Rich) and P0175 (Fuel Trim 2 - Too Rich). The vehicle runs smoothly once warmed up and does not exhibit any performance issues under normal driving conditions. I've already run Seafoam through the fuel tank with no improvement in cold starts or DTC behavior. Injector resistance tests show all injectors are within specifications. After clearing the codes, they reappear after approximately 80 miles of driving. I suspect a connection between the cold start difficulty and the rich fuel trim readings, as both symptoms began simultaneously following the fuel pump replacement. I'm seeking guidance on next steps for diagnostics—particularly what to look for in freeze frame data—and whether any specific sensor values (such as LongFT1/LongFT2, ECT, or O2 sensor voltages) might indicate a root cause. I’ve tested fuel pressure and found it remains steady at around 35 psi under normal conditions. However, during a KOEO (Key On, Engine Off) test, the pressure dropped to 32 psi over five minutes—suggesting potential fuel system leakage or inadequate pump output. The MAF sensor consistently reads 0 lb/s across multiple tests, even after cleaning. I’ve also checked for air leaks between the air filter and throttle body with no success. Any insights into possible causes related to post-fuel-pump replacement issues would be greatly appreciated.

Related fault codes

P0172P0175

Comments (4)

Anonymous 2016-12-17 13:51

P0172 and P0175 indicate the engine is running rich. Have you checked your live data with a scanner? Focus on LongFT1, LongFT2, ECT temperature, and O2 sensor voltages. Perform a fuel pressure test under KOEO to observe any drop over five minutes. Also consider cleaning the MAF sensor—ensure it's not using an oiled air filter, as cold engines naturally run rich and may trigger these codes.

Anonymous 2017-01-20 14:05

I returned to my 2010 Lincoln Navigator after a neck injury. I tested fuel pressure over five minutes with the engine warm—results remained steady at about 35 psi. While driving, I recorded live data and observed: (A) LongFT1 stayed consistently at -25, while LongFT2 fluctuated between -24.2 and -22.7; (B) ECT temperature remained stable at 383 K (~383°F); (C) O2 sensor voltages typically ranged from 0.025 to 0.855 volts, with minimal variation. Notably, the MAF reading stayed at 0 lb/s across three separate tests. I cleaned the MAF sensor but saw no improvement. Any additional advice would be very helpful.

Anonymous 2017-01-20 15:27

I need to verify fuel pressure—35 psi seems low for a 5.4L engine; typical specifications are often in the 50+ psi range. Double-check this with a calibrated gauge. Did you perform a KOEO test to observe fuel pressure drop over five minutes? The ECT reading of 383 K (~190°F) may be inaccurate—confirm it's properly measured and consider using Fahrenheit for clarity. The negative LongFT readings (e.g., -25) suggest the engine is actively reducing fuel delivery to compensate for a rich condition, which aligns with P0172/P0175. Regarding MAF: you report no additional codes—this may point to a sensor malfunction or wiring issue.

Anonymous 2017-01-23 15:11

Confirmed: fuel pressure remained at 32 psi during the KOEO test over five minutes. ECT temperature fluctuated between 365–385°F (approximately 185–196°C). The MAF sensor still reads 0 lb/s, though I occasionally saw transient readings when not actively monitoring. Only P0172 and P0175 are present. I’ve inspected the air intake path between the filter and throttle body and found no visible leaks. Symptoms remain consistent—cold start difficulty and persistent rich trim codes that return after a few days. The issue began immediately after fuel pump replacement, so I’m unsure how this change could have triggered these symptoms. Any suggestions on possible root causes or diagnostic steps would be highly appreciated.