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P1151 Fault with 1997 Ford Ranger V6 4.0L: Causes, Misfire Codes & Diagnosis Tips

Model: 1997 Ford Ranger Fault Code: P1151 Posted: 2015-12-28 14:01

Hi everyone, My 1997 Ford Ranger V6 4.0L has recently triggered a P1151 fault code along with two cylinder misfire codes (P0302 and P0306). I replaced the spark plugs and ignition wires, assuming it was a simple issue, but after just a few hundred miles, the same codes returned — and the new plugs were already fouled. The cylinders affected are #2 and #6. I've checked fuel pressure and confirmed there's spark at both misfiring cylinders. However, the problem persists. Can anyone suggest potential root causes or diagnostic steps? Thanks for any insights!

Related fault codes
P1151
Comments (5)
Anonymous 2015-12-28 14:13

Are you using an oiled air filter? Please post all current fault codes. What brand spark plugs did you install? Which cylinders are fouling — and do they appear wet or black? If you have a diagnostic scanner, check the fuel trim (FT) values. Without one, verify fuel pressure is within range.

Anonymous 2015-12-28 15:01

Thanks for the reply. I currently use a K&N air filter — though it hasn't been oiled or cleaned in some time. The fault codes I'm seeing are P1151, P0302, and P03-06. I used Motorcraft spark plugs, which appeared black when inspected last time. Cylinders #2 and #6 were the ones misfiring.

Anonymous 2015-12-29 09:34

Ensure you're using the correct air filter and clean your MAF sensor if needed. For cylinder misfires, verify spark presence at cylinders #2 and #6. Also check fuel pressure — then perform a KOEO (Key On, Engine Off) pressure drop test: observe how much pressure drops in 3–5 minutes to assess for leaks or delivery issues.

Anonymous 2015-12-29 10:33

Yes, both cylinders #2 and #6 have confirmed spark. I'll now check the other cylinders as well — thanks for the help!

Anonymous 2016-10-11 17:21

I own a 1997 Ford Ranger 3.0L 4x4 with a P0122 code. I replaced the TPS sensor, but it still runs with rough idle and bogs during acceleration. Black soot is coming from the exhaust — indicating a rich mixture. Any suggestions for troubleshooting this issue?