1997 Ford Taurus 3.0L OHC V6 Misfire with P0172 Code - Fuel Trim Issues and Engine Performance

Could the fuel pressure be low? Check if it's within the recommended range (30-45 psi).

I own a 1997 Ford Taurus with the same model and year, but I'm seeing P0171. After replacing both oxygen sensors on Bank 1, there was no improvement. Do you have a P1131 code? I suspect low fuel delivery to Bank 1—some fuel from Bank 2 flows into Cylinder #3, so it runs well, while Cylinders 1 and 2 show no response. When I disabled both injectors, mileage stayed the same and hesitation persisted. The engine is running on four cylinders only. This has caused a 10% drop in fuel efficiency. The yellow 'Service Engine Soon' light started flashing about 10 days ago—why would this happen? Don't ignore it.

Don't ignore the flashing service engine light. Running on four cylinders is a serious issue and likely contributes to misfires, poor fuel economy, and potential long-term engine damage.

Fuel pressure is confirmed at just over 30 psi—within the standard range of 30–45 psi. This rules out low fuel pressure as a primary cause.

I recently performed a Mode 6 diagnostic test. Test $41 failed component $11 (DPFE sensor), with minimum value 63744 and actual value 35. Test $52 failed component $00, max value 0, actual value 11955. I'm not familiar with these test IDs but suspect a faulty oxygen sensor or related issue. I plan to scope the O2 sensors tomorrow.

Fuel pressure is normal—what about fuel flow volume? A restricted fuel line, especially Line One, could be causing delivery issues and should be checked.

Dragonheart: Test ID $41, Component $11 refers to the DPFE (Differential Pressure Feedback Emission) sensor—this is typically a dealer-installed part. Also inspect all fuel hoses for leaks or blockages. Test ID $52 may indicate a misfire issue in older 1990s models; double-check that the original post correctly reports the codes.

I can verify again, but I'm confident the diagnostic test results are accurate and relevant to my vehicle's symptoms.

edhsu1999: I don't believe a fuel flow issue is responsible because it would affect both banks equally. If there were a blockage, both Bank 1 and Bank 2 should show poor performance. This suggests the problem is more specific to one bank.

Thanks for all the input! I finally diagnosed it: O2 sensors were scoped—Bank 1 sensor was stuck at 0.2V with no switching, while Bank 2 showed normal switching but had a high voltage reading (around 1.25V). After replacing both pre-O2 sensors, the misfire persisted. Fuel trims remain at -18% for Bank 1 and now -6% for Bank 2. A compression test revealed that five of six cylinders were at 110 PSI, with one cylinder reaching 165 PSI. Repeating the test with oil squirted into each cylinder brought all readings to around 145 PSI—indicating worn piston rings. The engine has 388,000 km on it and is now scheduled for a full engine replacement.

For a 1997 model, before replacing the entire engine, consider resolving the P0172 code and fuel trim issues first. Re-evaluate vehicle performance after addressing these problems—don't invest significant time or money in such an aging vehicle without proper diagnostics.