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1998 Ford Explorer 5.0L V8 Misfire & OBD2 Codes P0401, P0405, P1309 - Diagnosis and Fixes

Model: 98 Ford Explorer Fault Code: P0401 Posted: 2007-07-23 16:32

I own a 1998 Ford Explorer with a 5.0L V8 engine, 2WD, and am experiencing persistent misfire issues, most noticeable at idle, along with a significant drop in fuel efficiency. The vehicle has triggered OBD2 diagnostic codes: P0401 (Exhaust Gas Recirculation System Flow Malfunction), P0405 (EGR Valve Position Sensor Circuit Range/Performance), and P1309 (Fuel Pump Control Circuit). I have already replaced the EGR solenoid, and am scheduled to replace the EGR valve this weekend. After replacement, I cleared the codes, but the misfire symptoms persist. The P0401 code has not returned, though P0405 remains unresolved. I'm particularly unsure about what P1309 means — is it related to fuel pump control? Any insight or guidance on diagnosing this issue would be greatly appreciated. Additionally, I've noticed drivability problems such as pinging (pre-ignition knock) under load or at higher speeds, which may be linked to the engine's aging condition.

Related fault codes
P0401P0405P1309
Comments (7)
Anonymous 2007-07-23 17:00

Before replacing components, it's important to properly diagnose the root cause. Start by reviewing the official OBD2 code explanation for P0401: https://www.obd-codes.com/p0401. After replacing the EGR solenoid, did you clear the stored codes? Has that resolved the misfire or other symptoms?

Anonymous 2007-07-23 17:01

Check dedicated forums for discussions on DPFE (Diesel Particulate Filter Efficiency) sensors in Ford Explorer models — a faulty DPFE sensor is a common cause of EGR-related codes like P0401 and P0405.

Anonymous 2007-07-23 17:23

Thanks for the tip. I've cleared the codes, but after driving approximately 100 miles, two codes returned: P0401 and P1309. The pinging issue persists under load or at higher speeds — this is consistent with what's described in some engine performance guides.

Anonymous 2007-07-23 19:49

Eques-FL wrote: 'I do experience the "You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds.' This is fairly common in older Ford Explorers, especially with high-mileage engines. My parents used a 4.0L Explorer that suffered severe pinging for years — one friend even reported it sounded like a diesel engine. Have you tried switching to different brands of gasoline or using higher octane fuel? It might help reduce pre-ignition.

Anonymous 2007-07-23 20:20

The vehicle ran smoothly until about a few months ago — I suspect that the 185,000-mile mark is starting to show signs of wear on internal engine components.

Anonymous 2007-07-24 06:14

A dirty Mass Air Flow (MAF) sensor can contribute to pinging and misfire. However, I've already ruled out the MAF sensor — it was replaced earlier. Vacuum leaks or other intake system issues may still be present.

Anonymous 2007-07-24 09:10

Not the MAF — that has been ruled out. The next step should be a thorough inspection of vacuum lines and connections to rule out any leaks contributing to misfire or EGR performance issues.