How Expedition Owners Fixed Misfires and Rough Idle for Good

How to Fix Spark Plug Issue

For 2020 Ford Expedition owners, spark plug issues often manifest as part of a broader drivability problem, with symptoms like misfires and rough idle. While the provided owner data doesn't isolate a single "spark plug issue" for the 2020 model, it reveals a critical diagnostic truth: spark plugs and their related components are frequently part of the solution when addressing misfires and performance problems. The real-world experiences from Expedition owners show that a systematic approach, starting with ignition components, is key. As one owner, wacoexpy, succinctly put it after solving their problem: "Either way, cleaning the wells, replacing plugs and coils solved my problem."

Symptoms

The symptoms that lead owners to investigate their spark plugs and ignition system are distinct and concerning. The most direct and alarming symptom is a misfire, often signaled by a blinking check engine light. This isn't a steady light; a blinking light indicates an active, severe misfire that can damage the catalytic converters. You may feel this as a pronounced shudder or jerk in the engine's operation, especially under acceleration or at idle.

A rough or unstable idle is another very common complaint. Your truck may feel like it's shaking or stumbling when stopped at a light. In some cases, this can progress to stalling at low speeds or idle, which is not only inconvenient but also a safety hazard. Owners have reported the vehicle dying in traffic or when coming to a stop, which immediately prompts a diagnostic check.

Beyond the feel of the drive, these ignition-related problems trigger diagnostic trouble codes (DTCs) that point you in the right direction. The most common codes will be generic misfire codes (like P0300 - Random Misfire, or P0301-P0312 indicating a specific cylinder) or codes related to the ignition system's operation. While investigating, you might also encounter unrelated codes, as one owner did: "When I took off the air box to look at the throttle, I then got a P0113 code, which is the Intake Air Temp sensor." This highlights how disturbing one system while diagnosing another can occur.

Finally, a general lack of power or poor fuel economy can be a more subtle, long-term symptom. The engine isn't firing correctly, so it's not producing power efficiently. You might find yourself pressing the accelerator harder for normal response or noticing your fuel gauge dropping faster than usual. These symptoms collectively create a strong case for inspecting the spark plugs, coils, and their environment.

Most Likely Cause

Based on the synthesis of owner experiences, the most likely cause behind symptoms mistaken for or related to a simple "spark plug issue" is carbon buildup and contamination in the spark plug wells, leading to misfires and poor performance.

The process is mechanical and environmental. Over time, debris, moisture, and oil can seep past valve cover gaskets or from other sources into the deep wells where the spark plugs sit on the Ford's engine. This contamination creates a path for the high-voltage spark to travel to ground (the cylinder head) instead of jumping the gap at the electrode inside the combustion chamber. This is called a "spark leak" or "flashover." When this happens, that cylinder doesn't fire, causing a misfire. The owner quote is explicit: cleaning the wells was a pivotal part of the fix. This isn't just about worn-out electrodes; it's about the integrity of the entire spark plug cavity. A fouled plug from oil or coolant (as hinted at in data about coolant leaks) would produce the same result, but the root cause is the contaminant entering the well.

How to Diagnose

Diagnosing this requires a methodical approach to avoid unnecessary parts replacement. First, you need an OBD-II scanner. This tool is non-negotiable. Plug it into the port under your dashboard and read the stored codes. Look specifically for misfire codes. A code like P0304 points directly to cylinder #4. This gives you a specific target. Clear the codes and take the truck for a short drive to see if the misfire code returns, confirming an active problem.

With a specific cylinder identified, the next step is a visual and physical inspection. You'll need a basic socket set, a spark plug socket (likely 5/8" or 14mm, but confirm for your engine), and a flashlight. Carefully remove the engine cover and the ignition coil for the misfiring cylinder. The coil is held down by a single bolt. Once removed, inspect the coil boot for any signs of cracking, carbon tracking (thin black lines), or oil contamination. Shine your flashlight down the spark plug well. Look for any visible oil, coolant, or debris pooling at the bottom.

The definitive diagnostic step is a substitution test. If you have a coil from another cylinder that is not misfiring (e.g., cylinder #1 is good, cylinder #4 is bad), swap their positions. Clear the codes again and drive. If the misfire code moves (e.g., now shows P0301), the coil is faulty. If the code stays on the original cylinder (P0304), the problem is with the spark plug or the well itself. At this point, you must remove the spark plug for inspection. Look for cracked porcelain, excessively worn or fouled electrodes, or signs of coolant or oil on the threads and tip. As owner Ulver discovered during their diagnostic journey, "So I think I do need to perform a compression test. I'm still getting a misfire (blinking engine light) this morning after changing out one spark plug and inspecting the boot and coil spring last night." This shows that if new plugs and coils don't solve it, deeper issues like low compression from an intake leak (another owner-identified cause) may be at play.

Step-by-Step Fix

Follow these steps to resolve spark plug well contamination and related misfires. Warning: Allow the engine to cool completely before starting.

1. Gather Tools and Parts: Ensure you have all new spark plugs (the correct type for your Expedition), a set of ignition coils (or at least one for the affected cylinder), dielectric grease, a torque wrench, a spark plug socket with a swivel and extensions, a socket set, and compressed air or a shop vacuum.
2. Disconnect the Battery: Always start by disconnecting the negative battery terminal to prevent any electrical shorts or accidental engine starts.
3. Remove Engine Cover and Coils: Unclip and remove the plastic engine cover. Using a socket, remove the bolt securing the first ignition coil. Gently wiggle and pull the coil straight up and out of its well. Immediately plug the hole with a clean rag to prevent debris from falling in. Repeat for all cylinders you plan to service.
4. Clean the Spark Plug Wells: This is the critical step owners emphasized. Remove the rag and use a blast of compressed air or the hose of a shop vacuum to thoroughly clean out each well. You must remove all loose dirt, sand, and debris. As one owner shared: "Either way, cleaning the wells, replacing plugs and coils solved my problem."
5. Remove Old Spark Plugs: Insert your spark plug socket with an extension down the well. Carefully loosen and remove the old spark plug. Inspect its condition—oil, coolant, or heavy carbon fouling confirms contamination.
6. Gap and Install New Plugs: Check the gap on your new spark plugs against your vehicle's specification (do not assume they are pre-gapped). Apply a small amount of anti-seize compound to the threads if the plugs are not pre-coated. Carefully thread each new plug in by hand to avoid cross-threading, then torque it to the manufacturer's specification (typically between 10-15 ft-lbs, but verify).
7. Prepare and Install New Coils: Apply a small dab of dielectric grease inside the rubber boot of each new ignition coil. This improves the seal and prevents moisture intrusion. Carefully push each coil down into its well until it seats fully over the spark plug. Install and tighten the hold-down bolt.
8. Reconnect and Test: Reinstall the engine cover. Reconnect the negative battery terminal. Start the engine and listen for a smooth idle. Use your OBD-II scanner to clear any historical codes and check for active codes. Take a test drive to ensure the misfire and rough idle are resolved.

Parts and Tools Needed

• Parts:
  • Spark Plugs: Motorcraft SP-580 or SP-593 (exact type depends on engine; verify with VIN). You need 6 for the 3.5L EcoBoost V6. Always replace all plugs at once.
  • Ignition Coils: Motorcraft DG-508 or equivalent aftermarket (e.g., Bosch). A set of 6 is recommended.
  • Dielectric Grease: Small tube.
  • Anti-Seize Compound (optional): Only if plugs are not pre-coated.
• Tools:
  • OBD-II Scanner
  • Basic Socket Set (3/8" drive)
  • Spark Plug Socket (5/8" or 14mm, with swivel)
  • Torque Wrench
  • Various Socket Extensions (3", 6")
  • Compressed Air Can or Shop Vacuum
  • Flashlight
  • Trim Removal Tool (for engine cover clips)

Real Owner Costs

The cost to address this ranges dramatically based on the repair path. For the DIYer, the parts are the main expense. A set of 6 quality spark plugs costs between $60-$90. A set of 6 ignition coils can range from $150 for budget options to over $400 for OEM Motorcraft parts. With a minimal tool investment, the total DIY cost typically falls between $210 and $500.

At a repair shop, labor adds significant cost. A standard spark plug replacement service might cost $200-$400 in labor. If coils are replaced, add another 1-2 hours of labor ($150-$300). Therefore, a full plug and coil replacement at an independent shop could easily cost $600 to $1,200 or more, depending on parts markup. Dealership prices will be at the highest end of this spectrum. These costs underscore the value of a proper diagnosis; simply replacing parts on a guess, as one owner noted, can be wasteful: "If I had more time in life, I would have done one fix at a time and perhaps saved money."

Prevention

Preventing a recurrence of spark plug well contamination is straightforward. First, adhere to the manufacturer's recommended spark plug replacement interval. For the Expedition's EcoBoost engine, this is typically around 100,000 miles, but consult your manual. Proactive replacement prevents performance degradation and allows you to inspect the wells.

During any engine service that exposes the valve covers, such as replacing a leaking valve cover gasket, ensure the new gasket is properly installed. A leaking valve cover gasket is a primary source of oil in the spark plug wells. Keep the engine cover clean and ensure its seals are intact to minimize dust and water ingress from above. Finally, when washing the engine bay, avoid directly spraying high-pressure water around the ignition coils and engine cover seams.

What Owners Say

Real experiences from FORD owners:

Success Stories

"I got the bosch adapter and it worked at first but will no longer connect. The bosch could provide more in terms of codes for other stuff but requires additonal purchase on top of the first hundred bucks." — studabaker (source)

"Either way, cleaning the wells, replacing plugs and coils solved my problem. If I had more time in life, I would have done one fix at a time and perhaps saved money." — wacoexpy (source)

"I checked connections, cleared the code, and it hasn't come back on yet. The rear lift gate is jammed closed, no idea why." — Chris Watkinson (source)

Owner Experiences

"So one of my neighbors owns a Midas in town, he ran a scan and it showed a misfire on cylinder 1. I called the dealership we bought the Expy from and told them what was going on, they told me to bring it in." — MO311FAN (source)

"I called the dealership we bought the Expy from and told them what was going on, they told me to bring it in. After about 45-1hr, they came and told me it was fixed, “it was a spark plug.” Couldn’t really ask exactly what the problem was because I was dealing with our sales lady." — MO311FAN (source)

"So I replaced both, Light stayed on. So I bought a scan tool. https://www.boschdiagnostics.com/diy/products/bosch-obd-1200 and went home to do some testing." — jpwhre (source)

Lessons Learned

⚠️ "So I think I do need to perform a compression test. I'm still getting a misfire (blinking engine light) this morning after changing out one spark plug and inspecting the boot and coil spring last night." — Ulver (source)

Pro Tips from Owners

💡 "Good. most say dont do that.. I say good, glad you did the same thing I did, LOL I also cut out the muffler and added a 2 chamber flowmaster and a polished stainless 4" tip." — ZombieSoldier (source)

💡 "I say good, glad you did the same thing I did, LOL I also cut out the muffler and added a 2 chamber flowmaster and a polished stainless 4" tip. I also did 22's with Nitto NT420S tires (hate the tires, gonna be replaced in next few weeks) Then I did the brake upgrade." — ZombieSoldier (source)

💡 "how many miles and have they ever been changed? i wouldnt say its necessary. just a long reach air gun would be better to get all the gunk out. just get the ratchet on there and lightly tap it to get it break off. make sure you hold onto both ends of the ratchet. you should be ok. do not remove the fuel rail with exposed spark plug holes i had an o ring get stuck inthere and previous owner left some gunked up electrical tape inthere too." — JuniorExp03EB (source)

Real Repair Costs

"So, I have an opportunity to buy an '03 from a guy I have known for a long time for $650. He is basically looking to get the tire value and the $150 the scrappers would give him out of it." — Stephen (source)

"He is basically looking to get the tire value and the $150 the scrappers would give him out of it. It has 2 known issues. #1 One of the power windows recently stopped working. #2 #8 cylinder has a minor coolant leak in the intake manifold above it." — Stephen (source)

"Ford Protect Premium Maintenance Plan I am getting the Ford Extended Service Plan 8 years, 150,000 miles, $100.00 deductible,$ 3,2400.00 I am also considering their maintenance plan Ford Protect Premium Maintenance Plan 8 years, 125,000 miles, $ 2,570.00 8 years, 150,000 miles, $ 3,300.00 Full synthetic oil changes at 7,500 miles." — Charlie Vretis (source)

FAQ

Q: How long does it take to replace spark plugs and coils? A: For a competent DIYer with the right tools, replacing all six spark plugs and coils on your Expedition takes about 2 to 3 hours. This includes time for careful cleaning of the wells. A professional mechanic at a shop can typically complete the job in 1.5 to 2 hours.

Q: Can I drive with a blinking check engine light (misfire)? A: No, you should not. A blinking check engine light indicates a severe, active misfire. Driving in this condition can cause immediate and costly damage to the catalytic converters, as unburned fuel is dumped into the exhaust system, causing them to overheat and melt internally. Reduce load, pull over safely if possible, and have the vehicle towed.

Q: Is spark plug well contamination a common issue on the Expedition? A: While not unique to this model, it is a very common root cause of misfires in many modern V6 and V8 engines where the plugs are buried deep in wells. The Expedition's design makes the wells susceptible to collecting debris and moisture over time, especially if maintenance is deferred.

Q: DIY vs mechanic—what's recommended for this job? A: This is a very manageable DIY job if you are comfortable with basic hand tools and following methodical steps. The savings are substantial. However, if you lack tools, workspace, or confidence in working on engine components, paying a professional is a wise choice to ensure it's done correctly. The key is proper diagnosis first, as emphasized by owners who found success: "I checked connections, cleared the code, and it hasn't come back on yet."

Q: I replaced one coil and plug, but the misfire came back. Why? A: This points to a deeper issue. The problem may not have been the original coil/plug, or a different cylinder is now failing. It could also indicate a problem not related to ignition, such as a fuel injector issue, a vacuum or intake leak (as mentioned in the owner data), or even a mechanical problem like low compression. Further diagnosis with a scanner and possibly a compression test is needed.

Q: Do I have to replace all coils if only one is bad? A: It is not strictly necessary, but it is highly recommended. Ignition coils are wear items and often fail in succession. If one has failed, others are likely nearing the end of their service life. Replacing all six ensures consistent performance, prevents a future breakdown, and saves you from having to repeat the labor-intensive disassembly process soon after.