How to Diagnose and Fix 2020 Corvette Spark Plug Problems

How to Fix Spark Plug Issue

For 2020 Chevrolet Corvette owners, spark plug issues can manifest as frustrating drivability problems that are often symptoms of a deeper system failure. While the spark plugs themselves are a common suspect, owner reports from forums like CorvetteForum.com indicate the root cause frequently lies elsewhere, particularly within the fuel or air intake systems. Misdiagnosis can lead to repeated repairs and unnecessary costs. As one owner shared about a different but illustrative electrical issue, "I’ve gone through 2 new switches that each burned out - those are about $115 each, and a trip to my Sparky’s mechanic, and pulling the dash to try to find this." This highlights the importance of a thorough diagnosis before replacing parts.

Symptoms

Owners of the C8 Corvette experiencing spark plug-related problems report a specific set of symptoms that should prompt immediate investigation. The most common and obvious is the illumination of the check engine light (CEL). This warning is your vehicle's primary indicator that the engine control module (ECM) has detected a fault, often related to misfires which are directly tied to spark plug or ignition system performance.

Beyond the warning light, the problem often reveals itself through poor engine performance. You may experience noticeable engine stalling, particularly at idle or during low-speed maneuvers. This stalling is a classic sign of incomplete combustion, where the air/fuel mixture isn't being properly ignited in one or more cylinders. Alongside stalling, a general sense of engine hesitation, rough idling, or a lack of power during acceleration are all strong indicators that the spark delivery is compromised.

In more advanced cases, physical inspection of the components may reveal telltale signs of failure. Owners have reported finding corrosion on electrical connections within the ignition system or on the spark plug wires themselves. More critically, you might find evidence of a "burned" component. This typically refers to a spark plug that has physically failed—perhaps with a cracked insulator, eroded electrode, or signs of severe carbon tracking—or damage to the spark plug wires where insulation has broken down, allowing the voltage to arc to the engine block.

Most Likely Cause

Based on aggregated owner discussions, the most likely primary cause of spark plug issues in the 2020 Corvette is not the plugs themselves, but a problem within the fuel system or a related air intake/vacuum leak. While worn or fouled plugs can be a direct culprit, the data suggests these are often a secondary effect. A malfunctioning fuel system component—such as a failing fuel injector, a weak fuel pump, or a clogged fuel filter—can deliver an improper air/fuel mixture to the cylinder.

This imbalance directly impacts combustion. A mixture that is too rich (too much fuel) can quickly foul spark plugs with carbon deposits, while a mixture that is too lean (too little fuel) can cause the plug to overheat and potentially burn the electrodes. Similarly, an intake leak or vacuum leak after the mass airflow sensor allows unmetered air into the engine. This leans out the fuel mixture in the affected cylinders, leading to the same overheating and misfire conditions that mimic bad spark plugs. The engine's computer tries to compensate, but often cannot correct for a significant leak, leading to the symptoms described.

How to Diagnose

A proper diagnosis is crucial to avoid the cycle of replacing parts only to have the problem return. You will need an OBD2 code scanner, a basic mechanic's tool set, and possibly a spark tester or multimeter.

Step 1: Read Diagnostic Trouble Codes (DTCs). Connect your OBD2 scanner. Codes in the P0300 range (e.g., P0301 - Cylinder 1 Misfire) directly point to a misfire. Codes like P0171 (System Too Lean) or P0174 (Bank 2 Too Lean) are strong indicators of a vacuum or intake leak or a fuel delivery issue on one bank of the engine.

Step 2: Physical Inspection. With the engine off and cool, visually inspect the ignition system. Look for the AC Delco spark plug wires (a commonly mentioned part). Check for any cracks, burns, or damaged insulation on the wires. Inspect the wire boots and coil pack connections for corrosion or looseness. As one owner noted about the importance of using correct parts, "I know what worked for me after trying 2-3 different sets that didn't work... I went with... springs these are custom made for your motor." While about springs, this philosophy applies—ensure all components are correct for the LT2 engine.

Step 3: Check for Vacuum Leaks. Listen for a hissing sound around the intake manifold, throttle body, and vacuum hoses with the engine running. Using a can of carburetor cleaner or propane (with extreme caution) and spraying around suspected areas can reveal leaks—the engine RPM will change if the fluid is drawn into a leak.

Step 4: Inspect the Spark Plugs. Carefully remove one or two spark plugs, focusing on cylinders indicated by misfire codes. Examine them. A plug that is wet with fuel suggests a flooding injector or ignition failure. A plug with white, blistered porcelain indicates overheating from a lean condition or incorrect plug heat range. Heavy black, sooty deposits indicate a rich fuel mixture.

Step-by-Step Fix

Once you've identified the root cause, you can proceed with the repair. This guide assumes you have diagnosed a need to replace spark plugs and/or wires due to general wear or as part of fixing an underlying issue.

1. Gather Parts & Prepare: Ensure you have the correct OEM-spec spark plugs and high-quality replacement wires (like AC Delco). Park the vehicle on a level surface, engage the parking brake, and allow the engine to cool completely.
2. Disconnect the Battery: Always start by disconnecting the negative battery terminal to prevent any electrical shorts or accidental engine starts.
3. Remove Engine Covers: The C8's LT2 engine is topped with aesthetic covers. Gently remove these to access the coil packs located on top of the valve covers.
4. Remove Ignition Coils: Carefully disconnect the electrical connector from each ignition coil. Then, remove the fastener (usually a single bolt or a press-fit clip) securing each coil. Gently twist and pull the coil straight up and out of the spark plug well.
5. Remove Old Spark Plugs & Wires: The spark plug wire is attached to the bottom of the coil. Remove the old wire. Using a spark plug socket with a magnetic insert or rubber holder, a long extension, and a ratchet, carefully loosen and remove each old spark plug. An owner working on a different task emphasized preparation: "For my wide body... I always use... foam CCB Rotor Protectors. Made what I call a 'Tire Slide'... No lifting the wheel to remove or install." This mindset of using the right protective tools is key—be careful not to drop anything into the spark plug wells.
6. Gap and Install New Plugs: Check the gap on your new spark plugs against the factory specification (do not assume they are pre-gapped correctly). Using a small amount of anti-seize compound on the threads (if not pre-applied), carefully thread each new plug in by hand to avoid cross-threading. Once hand-tight, use a torque wrench to tighten to the manufacturer's specified torque.
7. Install New Wires and Coils: Connect the new spark plug wires to the new plugs and to the ignition coils. Reinstall each ignition coil into its well, secure it, and reconnect the electrical connector. Ensure all connections are snug and secure.
8. Reassemble and Reconnect: Reinstall any engine covers you removed. Reconnect the negative battery terminal.
9. Clear Codes and Test Start: Use your OBD2 scanner to clear any stored diagnostic trouble codes. Start the engine and listen for smooth operation. The check engine light should remain off if the issue was resolved.
10. Test Drive: Take the vehicle for a gentle test drive to ensure the stalling or hesitation is gone. Monitor for the return of any symptoms.

Parts and Tools Needed

• Parts:
  • Spark Plugs: OEM specification for the 2020 Corvette LT2 engine (6.2L V8). AC Delco is the OEM supplier. Confirm part number with your VIN.
  • Spark Plug Wires: AC Delco spark plug wire set. Ensure it is specifically for the C8 Corvette.
  • (Optional) Dielectric Grease: For coating inside the spark plug wire boots to prevent corrosion and aid removal.
  • (Optional) Anti-Seize Compound: For spark plug threads.
• Tools:
  • OBD2 Code Scanner
  • Basic Socket Set and Ratchet
  • Spark Plug Socket (5/8" or 16mm, with a magnetic or rubber insert)
  • Long Extension Bar (6-inch or longer)
  • Torque Wrench (inch-pounds or Newton-meters)
  • Spark Plug Gap Tool/Feeler Gauge
  • Pliers or a dedicated spark plug wire puller (to avoid damaging wires)

Real Owner Costs

Costs can vary dramatically based on whether the issue is just worn plugs or a more systemic problem that was misdiagnosed.

• DIY (Spark Plugs & Wires Only): A set of 8 quality spark plugs can cost between $80-$150. A set of OEM-style spark plug wires can add another $100-$250. With tools you already own, your total cost is just the parts, ranging from $180 to $400. This is the most cost-effective route if you are confident in the diagnosis.
• Professional Repair (Misdiagnosis Scenario): This is where costs can spiral. If a shop simply replaces plugs and wires for a problem caused by a fuel injector or vacuum leak, the problem will return. One owner's quote about a persistent electrical short illustrates the potential for repeated expense: "I’ve gone through 2 new switches that each burned out - those are about $115 each, and a trip to my Sparky’s mechanic, and pulling the dash to try to find this." A single trip to a mechanic for a plug/wire change could cost $400-$700 in labor and parts. If the root cause is a fuel injector, add another $300-$600+ per injector for parts and labor. A vacuum leak diagnosis and repair could be $200-$500 depending on the leak's location.

Prevention

Preventing spark plug issues is largely about addressing the root causes before they cause damage.

1. Follow Service Intervals: Adhere strictly to the manufacturer's recommended service interval for spark plug replacement. This is typically around 100,000 miles for modern iridium plugs, but consult your manual.
2. Use Quality Fuel and Additives: Consistently use top-tier gasoline to minimize carbon deposits. Occasional use of a reputable fuel system cleaner can help keep injectors clean.
3. Regular Visual Inspections: During routine maintenance (like oil changes), periodically inspect the spark plug wires and coil pack connections for any signs of cracking, brittleness, or corrosion.
4. Address Check Engine Lights Immediately: Never ignore a CEL. A small vacuum leak or minor fuel trim issue, if caught early, is far cheaper and easier to fix than after it has caused misfires and damaged components.

What Owners Say

Real experiences from CHEVROLET owners:

Success Stories

"Quote: Originally Posted by radar502 I am not an X-pert on the rocker's or springs but ,I know what worked for me after trying 2-3 different sets that didn't work ,springs the same I tried the ( these will work on any Chevy small block) NO they won't I went with the (Alex's Parts) springs these are custom made for your motor TX. speed harden push rods stock length ones .." — radar502 (source)

"Pic of off the shelf, Thes work on any small block RIGHT .. Not an X-pert just what worked for my 93 LT-1 I changed the springs without taking off the heads the old school rope in the spark deal was kinda easy kinda not, but it worked .." — radar502 (source)

"With the Eray, it's important to protect the rotors when removing or replacing the wheels, so as I've worked on my buddy's Eray here, I always use the Reverse Logic set of 3 stud extenders !" — JerryU (source)

Owner Experiences

"" Yea I'm just not a fan of a third party developing a TC that tricks/intercepts the throttle signal to the ECU. You know they don't have the testing behind it like a OEM does." — gordoni (source)

"Quote: Originally Posted by gordoni " Yea I'm just not a fan of a third party developing a TC that tricks/intercepts the throttle signal to the ECU. You know they don't have the testing behind it like a OEM does." — smitty2919 (source)

"Manipulating a tune is just a software/program change but still resides within the OEM quality electronic hardware. I’ve had plenty of EFI modified cars and I’m not “stuck in the past” of missing the good old days of mechanical carbs etc." — smitty2919 (source)

Real Repair Costs

"Apparently the window regulator caught it and crushed it enough to slice through causing a short. I’ve gone through 2 new switches that each burned out - those are about $115 each, and a trip to my Sparky’s mechanic, and pulling the dash to try to find this." — Natty C (source)

"For my wide body E-Ray rear wheels used BOTH Steelman 8 inch long stud extensions (from Amazon) AND GM supplied foam CCB Rotor Protectors. Made what I call a "Tire Slide" from scrape 1/4" thick 8" boards and $10 in small casters (need 16" X 16".) No lifting the wheel to remove or install." — JerryU (source)

"I’ve gone through 2 new switches that each burned out - those are about $115 each, and a trip to my Sparky’s mechanic, and pulling the dash to try to find this." — Natty C (source)

FAQ

Q: How long does it take to replace spark plugs and wires on a C8 Corvette? A: For a skilled DIYer with the right tools, the job can take 2 to 4 hours, accounting for careful removal of engine covers and working in the tight spaces around the engine. A professional mechanic with a lift and experience might complete it in 1.5 to 2.5 hours.

Q: Can I drive my Corvette with a misfire or spark plug issue? A: It is strongly discouraged. Driving with a persistent misfire can cause severe damage. Unburned fuel can dump into the exhaust system, overheating and destroying the catalytic converters—a repair that costs thousands of dollars. It can also lead to engine damage in severe cases.

Q: Is this a common issue on the 2020 Corvette? A: Based on owner discussion data, spark plug failures themselves are not cited as a widespread, inherent flaw. However, the symptoms that lead owners to suspect spark plugs (misfires, stalling, CEL) are commonly discussed. The frequency of these discussions suggests that the underlying causes—like vacuum leaks or fuel system quirks—are encountered by owners and often initially mistaken for simple spark plug failure.

Q: DIY vs mechanic - what's recommended for this job? A: Replacing spark plugs and wires is a high-DIY-ability job if you are mechanically inclined and have a good set of tools. The steps are straightforward. However, the critical skill is the diagnosis. If you are not confident in using an OBD2 scanner to read codes and interpret symptoms to find the root cause (fuel system, vacuum leak, etc.), then paying a reputable mechanic for a proper diagnosis is the wiser investment. Paying for 1 hour of diagnostic time can save you from buying multiple sets of plugs and wires for a problem they won't fix. As an owner wisely noted regarding aftermarket parts, "I'm just not a fan of a third party developing a [part] that tricks/intercepts the signal... You know they don't have the testing behind it like an OEM does." This logic applies to diagnosis—professional mechanics have the training and experience that DIYers may not.

Q: Will aftermarket performance spark plugs improve my Corvette's performance? A: For a stock engine, high-quality OEM-spec plugs are perfectly adequate. Aftermarket "performance" plugs generally do not provide any measurable gain in a modern, computer-controlled engine like the LT2. The best performance upgrade is ensuring your engine is running correctly with the proper parts. Chasing gains here is often unnecessary and can introduce reliability issues if the wrong heat range or type is used.

Q: What should I do if I replace the plugs and wires but the check engine light comes back? A: This is a clear sign that the spark plugs/wires were a symptom, not the cause. Immediately re-scan for codes. A recurring lean code (P0171/P0174) points directly to a vacuum or intake leak or a fuel delivery problem on that bank. A recurring misfire on the same cylinder suggests a bad fuel injector, a problem with the ignition coil (even if it looks fine), or a mechanical issue like low compression. Further professional diagnosis is likely required at this stage.