← Back to list

2003 Ford Focus Zetec P0304 Fault Code: Rough Running and Low Power Diagnosis

Model: 2003 ford focus zetec Fault Code: P0304 Posted: 2020-04-19 14:37

My 2003 Ford Focus Zetec is experiencing rough idle and significantly reduced power across all engine loads. The check engine light flashes intermittently, especially under higher load conditions. I've also noticed a P0171 code appearing alongside the P0304 code. I have already replaced the coil pack and ignition wires for cylinder 4, and I swapped spark plugs between cylinders 1 and 4—however, the P0304 fault code persists specifically on cylinder 4. What should my next troubleshooting steps be? Any insights or recommendations would be greatly appreciated.

Related fault codes

P0304

Comments (2)

Anonymous 2020-04-19 16:32

Could you please share your fuel trims (LT and ST) as well as the MAF sensor readings at idle and at 3000 RPM? This data will help determine if there's a lean condition or misfire related to fuel delivery, which may be contributing to the P0304 code.

Anonymous 2020-04-19 19:47

I'm unable to provide those readings at this time. I only used an OBD-II scanner briefly to retrieve fault codes. I'm planning to purchase my own scanner soon. In the meantime, I've discovered a missing vacuum hose and a potential fuel injector wiring issue—both of which may be contributing to the misfire. I'll inspect these components today and update with my findings (good, bad, or indifferent) by tomorrow evening. Thank you for your prompt response—I look forward to further discussion.