2020 Ford F-150 Misfire? Spark Plug & Fuel System Troubleshooting

How to Fix Spark Plug Issues on Your 2020 Ford F-150

The 2020 Ford F-150 is a reliable truck, but like any vehicle, it can experience issues over time. Spark plug problems, leading to symptoms like misfires and rough idling, are among the concerns some owners have faced. As one owner reported: "Bought mine at 50k, now at 120k, oil changes every 5k and I did spark plugs a couple weeks ago (I think it was probably still on the originals), and that's literally the only thing I've ever had to touch under the hood." — NotoriousCFR [source: https://reddit.com/r/f150/comments/1q02ker/ecoboost_question/nwutfjy/]. Let's dive into the symptoms, causes, and solutions for spark plug-related issues in this model year.

Symptoms

Several symptoms can indicate spark plug problems in this F-150. One of the most common is misfiring. This occurs when one or more cylinders in the engine fail to ignite the air-fuel mixture properly. You might notice a jerking or sputtering sensation, especially during acceleration. The check engine light may also illuminate, potentially with a code indicating a misfire in a specific cylinder.

Another symptom is a rough idle. When the engine is idling, it should run smoothly and consistently. If the spark plugs are worn or fouled, the engine may vibrate excessively or run unevenly. This can be more noticeable when the truck is stopped at a traffic light or parked. One owner described experiencing a "rough idle" after hitting 80k miles.

Starting issues can also point to spark plug problems. Worn or damaged spark plugs can make it difficult for the engine to start, especially in cold weather. The engine might crank for an extended period before finally starting, or it might fail to start altogether. Some owners have noted the engine "only revs once and doesn't come on the first try," which may also be linked to a rough idle, as stated by an F-150 owner.

Rattling or clunking noises, while less directly related, can sometimes accompany spark plug issues. A misfire can cause vibrations and abnormal combustion, which might manifest as unusual noises coming from the engine. These noises can be hard to pinpoint, but they should prompt further investigation, especially if they are accompanied by other symptoms mentioned. One owner even mentioned a rattle on start-up, which may or may not be related. "I just hit 80k miles. The only thing I've had issues with is a rough idle and occasionally when I go to start it only revs once and doesn't come on the first try." — iamMRawkward [source: https://reddit.com/r/f150/comments/1pxeevt/new_owner_2021_xlt_70k_miles/nwaqfes/].

Most Likely Cause

Based on owner reports, a likely contributing factor to spark plug issues in your truck is related to the fuel system. While not always the direct cause of spark plug failure, fuel system problems can lead to fouled or damaged plugs. This can stem from issues like improper fuel delivery, poor fuel quality, or problems with fuel injectors, all of which can affect the combustion process and lead to premature spark plug wear.

A fuel system issue can cause the air-fuel mixture to be too rich or too lean. A rich mixture, where there's too much fuel, can lead to carbon buildup on the spark plugs, reducing their ability to ignite the mixture. Conversely, a lean mixture, where there's not enough fuel, can cause the engine to run hotter, potentially damaging the spark plugs and other components. Both scenarios create an unhealthy environment for spark plugs and can reduce their lifespan.

It's important to remember that fuel system issues are often intertwined with other components, such as the rings. If the fuel is not burning correctly, it could lead to an issue with the rings needing replacement.

How to Diagnose

Diagnosing a spark plug problem on the vehicle involves a systematic approach. Start by visually inspecting the spark plugs. Remove each spark plug and examine its condition. Look for signs of wear, damage, carbon buildup, oil fouling, or other abnormalities. A healthy spark plug should have a clean, dry appearance with minimal wear on the electrodes.

Next, check the spark plug gap. The gap is the distance between the center and ground electrodes, and it needs to be within the manufacturer's specifications. Use a spark plug gap tool to measure the gap and adjust it as needed. An incorrect gap can cause misfires and other performance issues. Refer to your owner's manual for the correct spark plug gap for the engine in this F-150.

A compression test can help rule out other potential causes of misfires, such as worn piston rings or valve problems. Use a compression tester to measure the compression in each cylinder. The readings should be within a specified range, and there should be minimal variation between cylinders. Low compression in one or more cylinders can indicate a more serious engine problem.

Finally, use an OBD-II scanner to check for diagnostic trouble codes (DTCs). A misfire will often trigger a DTC that can help pinpoint the affected cylinder. The scanner can also reveal other codes related to the fuel system or other engine components that may be contributing to the problem. Pay attention to codes related to fuel trims, oxygen sensors, and other fuel-related parameters.

Tools needed for this diagnostic process include:

• Spark plug socket
• Socket wrench
• Spark plug gap tool
• Compression tester
• OBD-II scanner

Step-by-Step Fix

If you've identified a spark plug problem and decided to tackle the repair yourself, follow these steps:

1. Gather your tools and parts: Ensure you have the correct spark plugs, spark plug socket, socket wrench, torque wrench, spark plug gap tool, and any other necessary tools. As one owner shared: "Spark plug replacement 12k miles. This doesnt seem like a truck id ever want to own just because of all the do this dont do that must do this bull shit." — enraged768 [source: https://reddit.com/r/f150/comments/1pyc0c2/2025_shelby_f150/nwhouyd/]. Despite their comment, having the right tools makes the process smoother.
2. Disconnect the negative battery cable: This is a crucial safety step to prevent electrical shocks or damage to the vehicle's electrical system.
3. Locate the spark plugs: The spark plugs are typically located on top of or on the sides of the engine. Refer to your truck's service manual for the exact location.
4. Remove the coil packs: Each spark plug has a coil pack attached to it. Disconnect the electrical connector from the coil pack and then unbolt or unscrew it from the engine.
5. Remove the old spark plugs: Use the spark plug socket and socket wrench to carefully remove the old spark plugs. Be sure not to damage the threads in the cylinder head.
6. Inspect the spark plug wires or coil boots: Check the condition of the spark plug wires (if equipped) or coil boots for any signs of damage or wear. Replace them if necessary.
7. Gap the new spark plugs: Use the spark plug gap tool to set the gap of the new spark plugs to the manufacturer's specifications.
8. Install the new spark plugs: Carefully thread the new spark plugs into the cylinder head by hand to avoid cross-threading. Then, use the torque wrench to tighten them to the specified torque.
9. Reinstall the coil packs: Reattach the coil packs to the engine and reconnect the electrical connectors.
10. Reconnect the negative battery cable: Once all spark plugs have been replaced, reconnect the negative battery cable.
11. Start the engine and check for misfires: Start the engine and listen for any signs of misfires or unusual noises. Use an OBD-II scanner to check for DTCs.

It's always a good idea to double-check your work and consult the vehicle's service manual for specific instructions and torque specifications. Remember the owner's experience: "After replacing sparkplugs and coils; I've now got P0354 open circuit issue on 4. I also flushed trans and replaced filter only for the damn thing to start shuddering at acceleration but no error codes." — Simple_Expression604 [source: https://reddit.com/r/f150/comments/1p8wkpp/2019_f150_50_misfire_only_wot/nrpn0uu/]. While not the identical model year, it emphasizes careful work. As another owner suggests: "Swap coils 1 and 2, pull the spark plug for cylinder 1. If it’s all covered in oil, then the spark plug tube o gasket is damaged, and it needs to come back apart." — k0uch [source: https://reddit.com/r/f150/comments/1q0sukv/2017_f150_35_misfire_after_cam_phaser_replacement/nx0kfhm/].

Parts and Tools Needed

• Spark plugs (check your owner's manual for the correct type)
• Spark plug socket
• Socket wrench
• Torque wrench
• Spark plug gap tool
• OBD-II scanner
• Coil packs (if replacing)
• Rings

Real Owner Costs

The cost of replacing spark plugs on the vehicle can vary depending on whether you do it yourself or take it to a mechanic. If you choose the DIY route, the cost will primarily be for the parts. Spark plugs typically range from $5 to $20 each, depending on the brand and type. A set of six spark plugs would therefore cost between $30 and $120.

If you decide to have a mechanic replace the spark plugs, the cost will include both parts and labor. Labor costs can vary depending on the shop's hourly rate and the complexity of the job. Expect to pay between $150 and $400 for a spark plug replacement at a mechanic.

Some owners may also choose to replace the coil packs at the same time as the spark plugs, especially if they have a high mileage or if the coil packs are showing signs of wear. Coil packs can range from $30 to $100 each, so replacing all six coil packs could add an additional $180 to $600 to the cost.

Here are some examples of real owner costs:

• DIY spark plug replacement: $50 (parts only)
• Mechanic spark plug replacement: $250 (parts and labor)
• DIY spark plug and coil pack replacement: $300 (parts only)

Prevention

To prevent spark plug problems in the vehicle, follow these maintenance tips:

• Follow the recommended maintenance schedule: Adhere to the manufacturer's recommended maintenance schedule for spark plug replacement. This will help ensure that the spark plugs are replaced before they become excessively worn or fouled.
• Use high-quality fuel: Use high-quality fuel from reputable gas stations. This will help prevent fuel system problems that can lead to spark plug fouling.
• Address fuel system problems promptly: If you notice any signs of fuel system problems, such as rough idling or misfires, address them promptly. This can help prevent damage to the spark plugs and other engine components.

What Owners Say

Real experiences from FORD owners:

Owner Experiences

"Bought mine at 50k, now at 120k, oil changes every 5k and I did spark plugs a couple weeks ago (I think it was probably still on the originals), and that's literally the only thing I've ever had to touch under the hood." — NotoriousCFR (source)

"Spark plug replacement 12k miles. This doesnt seem like a truck id ever want to own just because of all the do this dont do that must do this bull shit." — enraged768 (source)

"The only thing I've had issues with is a rough idle and occasionally when I go to start it only revs once and doesn't come on the first try. I did a coolant flush and transmission oil drain and fill at 70k." — iamMRawkward (source)

FAQ

Q: How long does it take to fix a spark plug issue?

A: Replacing spark plugs can take anywhere from 1 to 3 hours, depending on your experience and the complexity of the engine layout.

Q: Can I drive with a misfire?

A: Driving with a misfire is not recommended. It can damage the catalytic converter and other engine components. Address the issue as soon as possible.

Q: Is this a common issue on the 2020 Ford F-150?

A: While not exceptionally widespread, spark plug issues can occur on this F-150, particularly as the vehicle ages and accumulates mileage. Regular maintenance can significantly mitigate this risk.

Q: DIY vs mechanic - what's recommended?

A: Replacing spark plugs is a relatively straightforward task that many owners can do themselves. However, if you are not comfortable working on your vehicle or if you suspect a more serious underlying issue, it's best to take it to a qualified mechanic. A mechanic can properly diagnose the problem and ensure that the repair is done correctly. Considering one owner's comment: "^this is a thing that happens on fords where extremely worn spark plugs require the coils to work harder therefore drawing more current from the ignition driver in the pcm causing it to become damaged." — cock-mongrel [source: https://reddit.com/r/f150/comments/1py2ie0/i_am_at_a_loss/nwgu7u5/], it may be wise to consult a professional.