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2004 Ford Explorer P0302 Misfire After Installing New Spark Plugs and Wires

Model: 2004 Ford Explorer Fault Code: P0302 Posted: 2017-04-04 05:29

Hi, I recently installed new spark plugs and wires on my 2004 Ford Explorer. The truck was running fine before the replacement. However, after the work, the check engine light came on with code P0302 — indicating a misfire in cylinder #2. At low RPMs, I notice a noticeable vibration, and there's a noise coming from near the passenger side of the engine where cylinder #2 is located. The truck starts normally but shakes slightly when driving, especially during acceleration. I've also noticed minor backfiring and power loss at stoplights. I'm wondering if this could be related to the plug or wire installation — or if there's another underlying issue? Any advice on troubleshooting this would be greatly appreciated.

Related fault codes
P0302
Comments (12)
Anonymous 2017-04-04 12:43

First, verify the work done during the recent repair. This is a 4.0L engine, right? Check for spark at cylinder #2 — it's the center plug on the passenger side.

Anonymous 2017-04-04 13:26

Yes, it's a 4.0L. I've cleared the codes and ran another diagnostic test, and now P0316 appears — indicating a misfire at startup. That means cylinder #6 might be involved too. I'm also experiencing power loss during startup. Any suggestions?

Anonymous 2017-04-04 13:27

Is cylinder #2 located on the passenger side?

Anonymous 2017-04-04 13:41

P0316 indicates a misfire at engine start — see https://www.obd-codes.com/p0316. Are you still seeing P0302? Did you install OEM-quality spark plugs (not cheap aftermarket parts)? Regardless, carefully review the installation process — especially coil and wire routing.

Anonymous 2017-04-04 16:36

I'm not fully experienced with this, so I'm trying to learn. I used platinum spark plugs — are there better options recommended?

Anonymous 2017-04-04 17:05

Yes, that's the right approach — avoid cheap, low-quality parts. Since the truck ran fine before the plug and wire replacement, double-check the installation process. Ensure no components were moved or misrouted during access to the coil packs.

Anonymous 2017-04-05 08:19

It's now stable. My mechanic reviewed everything. The engine starts properly and runs smoothly under normal conditions. However, when I shift into drive, it shakes slightly and loses power during acceleration. It seems to regain power while driving but still has a minor misfire and occasional backfiring. At stoplights, the shaking returns — though I can still pull away. What do you think? This is my first time troubleshooting this level of issue.

Anonymous 2017-04-05 11:19

I suspect the plug replacement triggered the problem. Recheck all installation steps. A backfire after new plugs suggests a misrouted spark wire — but you said the secondary ignition components (plugs and wires) are intact. If no new codes appear, use an OBD2 scanner to monitor engine data: ECT, MAP, MAF, fuel trims, and oxygen sensor readings. A vacuum leak could explain these symptoms. Try a classic 'vacuum leak test' using carburetor cleaner — search for tutorials online with the term "vacuum leak check with carb cleaner".

Anonymous 2017-04-05 15:46

Thanks! I thought about vacuum leaks too. We’ve already checked all wires and reviewed the wiring diagram you sent. Next step is to perform a vacuum leak test. I’ll watch tutorials on YouTube for that. Thanks again!

Anonymous 2017-04-06 10:32

It was actually the spark plugs — after completing a vacuum check (no leaks), we rechecked the wires and plugs. We replaced them with higher-quality ones, and now everything is back to normal. Thanks for your help.

Anonymous 2017-04-06 10:58

Great to hear you resolved it! A key point: using quality parts — such as OEM spark plugs — makes a significant difference in performance and reliability.

Anonymous 2017-04-06 13:59

Yes, absolutely. That's why I didn’t need to replace them again — they’re holding up well now. Thanks for the advice!