P1167

P1167 in the Ford definition is a fuel-trim lean code on bank 1 that escalates beyond the generic P0171 — the PCM has corrected long-term fuel trim past roughly +25% and held it there long enough to trigger this stricter Ford-specific lean threshold. The cheapest-first diagnostic ladder is the same as a P0171 with a sharper edge: (1) Smoke-test the intake — sustained LTFT north of +20% on a Ford is 80% of the time a torn intake-manifold gasket, a cracked PCV hose, or a brittle vacuum tee. Cap the throttle body and pump 0.5 psi of smoke; anything visible at the PCV port, the brake booster line, or the IMRC/IMT actuator vacuum lines is the leak. (2) Check MAF g/sec at idle — Ford 4.6/5.4L should see 5-8 g/sec at warm idle, EcoBoost 3.5L should see 3-5 g/sec at idle and climb proportionally with rpm; under-reporting MAF starves fuel and creates a false lean signal. (3) Dead-head a fuel-pressure gauge on the rail — port-injected Fords spec 55-65 psi at idle, EcoBoost direct-injection low-side spec 50-65 psi with HPFP-side commanded as needed; below spec means weak FPDM/pump or restricted filter sock. Don't condemn the long-block for a stuck-open EGR or a leaking fuel-injector seal until you've read keep-alive memory for an unauthorized-tune flag — aftermarket tunes that disable the rear-bank O2 monitor or rescale the MAF transfer function can mimic a hardware lean condition and waste hours of misdiagnosis.

Vehicle-specific patterns: 2004-2010 Ford F-150 / Expedition 5.4L 3V Triton is the canonical P1167 victim — the plastic intake-manifold gasket at the rear cylinders cracks around 80-120k miles and pulls a localized vacuum leak that pegs bank 1 lean; Ford issued multiple TSBs and the updated composite manifold gasket is the fix. 2007-2010 Ford Edge / Lincoln MKX 3.5L Duratec throws P1167 from a cracked plastic intake manifold at the runner-to-plenum joint. 2011-2016 Ford F-150 EcoBoost 3.5L commonly throws P1167 from intake-valve carbon (no port-injection wash) starving cylinders 1 and 4 of air-fuel mix homogeneity; walnut-blast service is the fix. 2008-2011 Ford Focus 2.0L Duratec throws P1167 from a brittle PCV elbow that cracks at the valve cover. Estimated repair: $180 (PCV elbow + intake gaskets DIY) to $1,400 (intake manifold replacement + gaskets on a 5.4L 3V with shop labor).