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1997 Ford Ranger P0171 P0301 P0304 - Misfire at Idle and Low RPM, Spark Check Confirmed

Model: 1997 ford ranger Fault Code: P0171 Posted: 2008-11-18 00:51

My 1997 Ford Ranger is exhibiting a misfire issue that worsens during gear shifts when engine RPMs drop. The truck runs smoothly on the highway but misses significantly at idle. I've already replaced the spark plugs, and when I disconnect the ignition wire for cylinder #1, there's no noticeable change in performance — indicating no significant misfire from that cylinder. The vehicle is showing diagnostic codes P0171 (rich mixture), P0301 (misfire detected in cylinder 1), and P0304 (misfire detected in cylinder 4). I have confirmed good spark at the plug, but the issue persists. Given the age of the truck and engine configuration, I'm wondering if the problem lies with worn ignition components or underlying mechanical issues such as valve seating or compression loss.

Related fault codes

P0171P0301

Comments (5)

Anonymous 2008-11-18 23:35

What engine type does your 1997 Ford Ranger have, and what is the current mileage?

Anonymous 2008-11-21 23:29

4.0L V6 engine, approximately 115,000 miles

Anonymous 2008-11-25 23:11

New spark plug wires would be my next step, you obviously have no spark to one, possibly two cylinders. As I recall, the plug wires on this engine are routed right next to some very hot engine parts. I would make sure they're not touching anything and getting burned.

Anonymous 2008-11-26 17:54

Have you performed a compression test? I recently replaced two cylinder heads, and both had valves seated too deeply into the head — this could be a common issue on older 4.0L engines at around 115k miles.

Anonymous 2008-12-02 22:47

I've just done a compression test and replaced the spark plug wires, but the P0301 code remains. I still have good spark at the plug — the misfire is likely mechanical or related to fuel delivery or intake system issues.