2005 Ford F150 Cold Start Misfire & Lean Codes: PO171, PO174, PO302 Fix Guide

Perform a KOEO fuel pressure test—check for drops of X psi within five minutes after engine shutdown. Consider adding a fuel treatment like Techron or SeaFoam to clean injectors and improve combustion. Also, clean the MAF sensor; avoid using oiled air filters. Use your Autel AL319 scanner to monitor ECT, fuel trims, and O2 sensor voltages for live data during cold starts.

Thanks for the tip! I’ll clean the MAF sensor tomorrow and switch to non-ethanol fuel. I’ve got an Autel AL319 OBD-II & CAN scanner that captures ECT, fuel trims, and O2 voltages via live data and freeze frame. I’ll also check my air filter—installed by a mechanic, so I’m not sure if it’s oiled.

If professionally installed, the air filter is likely correct. Cold mornings place high demands on fuel system pressure and volume during startup. Ford engines often suffer from vacuum leaks causing PO171 and PO174. See more details at https://www.obd-codes.com/p0171.

The temperature dropped to freezing overnight. The truck started fine but developed a PO302 (cylinder 2 misfire) after driving two miles. I switched to non-ethanol fuel, and the issue disappeared once warmed up. Still planning to get a fuel pressure gauge—where is the correct test point? How do I check for vacuum leaks in hoses or gaskets? Thanks again for your help.

An old-school method: use carb cleaner or brake cleaner while idling, spraying suspected leak areas such as mating surfaces and vacuum lines. If engine sound or RPM changes, it indicates a vacuum leak. Don’t forget to inspect the PCV hose—on Fords, the elbow is a common failure point.

I cleaned the MAF sensor today, added non-ethanol fuel and injector cleaner to the tank. I inspected all hoses but didn’t see any obvious issues. I’ll try the carb cleaner trick tomorrow. This problem disappears when warm—possibly due to fuel line drainage overnight. I’m still looking for signs of a leak. Unfortunately, no gas pressure gauge available—the engine lacks an easy test port. Grrr!

No visible leaks found. Same issue this morning—now showing PO305 (cylinder 5 misfire).

Engine temperature: 140°F to 190°F. Short-term fuel trims: 0%, Long-term fuel trim 1: 7.8%; Short-term trim 2: 1.6%, Long-term trim 2: 6.3%. MAF reading: 0.03–0.05 lb/sec. O2 sensor B1S1: 0.360V, B2S1: 0.06V. Fuel pressure: 39 psi (EON), 0.40 psi (EOFF). All readings normal when warm—will retest with cold engine tomorrow morning.

After using one full tank of non-ethanol fuel and two bottles each of fuel conditioner and injector cleaner, the misfire issue has completely resolved. No codes appear now—the engine runs smoothly without any misfires or lean warnings.

Hope you see this… Did your problems ever return after that fix?

The original poster hasn’t responded since the last post.

Have you checked the EGR? A stuck or malfunctioning EGR can cause lean conditions and misfires. I had a similar issue on an older 4-cylinder engine—initially showed cylinder misfire and lean codes. It turned out to be a one-tooth jump in the timing belt, causing lean combustion and misfires. Once corrected, performance improved dramatically.

The 5.4L V8 engine in a 2005 Ford F150 does not have an EGR system—thank you for the suggestion though.

I’m experiencing a similar issue but with no error codes. The problem started after a PO307 (cylinder 7 misfire) code appeared. I replaced the coil pack, and it lasted only one day before returning—this time without any codes. I checked plugs and found two loose connections: cylinders 7 and 2. Tightened them up and applied dielectric grease to all coil pack springs. After driving a few miles, it seemed fine. This morning, it started normally but began idling roughly after about five minutes, with misfires during acceleration. Once warmed up, the issue disappears—though I still hear a slight misfire under heavy throttle. I’ll try cleaning the MAF sensor and adding injector cleaner to the tank tonight.

Can you identify which cylinder is misfiring? Cylinder 7 or another one now?

I can’t determine it because the vehicle isn’t throwing a code.

Is there a scanner available to check cylinder misfire counts? That might help pinpoint the issue.

I took it to Firestone. He’s uncertain whether it's a valve/head or timing issue—leaning toward head/valve since misfires occur only on cylinders 4 and 8. I did a compression test: all readings between 190–210 psi, with cylinders 4 and 8 at 209–210 psi. He suggested going to a Ford dealer, then when I said I wasn’t sure about paying, he recommended a leak-down test. Any thoughts on that?

A leak-down test is more accurate than a compression test—it identifies exactly where (if any) compression is leaking out.