Why Your 2020 Corvette Has a Slapping Noise and Gas Smell

How to Fix Timing Chain Issue

For owners of the 2020 Chevrolet Corvette, addressing a potential timing chain issue requires a methodical approach focused on diagnosis and precision repair. While direct reports of timing chain failure on the C8 Corvette are not widespread in our data, the principles of addressing engine timing and related mechanical noises are critical. The underlying theme from experienced owners is the importance of correct parts and procedures. As one owner, Tuna Joe, emphasized during a complex repair, "When I pulled the bell housing and trans, I realized I had the incorrect flywheel. It would have worked, but on EBay there was a NOS correct 11” flywheel with the correct date for a decent price." This attention to detail is paramount.

Symptoms

Owners describing potential drivetrain or timing-related issues report several key symptoms that should prompt immediate investigation. A prominent mechanical noise, often described as a slapping, tapping, or rattling sound from the engine bay, is the most direct indicator. This noise may change with engine speed and is typically most audible at idle or low RPMs. It should not be confused with normal valvetrain noise.

Another symptom reported is a noticeable smell of gasoline. This can be particularly concerning as it points to a potential fuel system issue, which owners have directly linked to engine performance problems. A fuel smell, especially when combined with unusual noises, suggests a leak or a rich-running condition that could place additional stress on engine components. Some owners also mention a general sense of anxiety about their vehicle's condition, which is a valid emotional response to hearing unfamiliar and potentially serious mechanical sounds from a high-performance engine.

Less direct but still relevant symptoms include observations about other components during investigation. Owners have noted issues with rollers, idle quality, and even ancillary parts like a passenger headlight motor or front-end components when they have the vehicle apart for related work. The presence of any fluid drip, particularly oil from the front timing cover area, can also be a sign of a seal failure associated with the timing chain assembly.

Most Likely Cause

Based on analysis of owner discussions, the most likely root cause of symptoms that could be mistaken for or lead to a timing chain issue is a fuel system malfunction. Owners have directly identified the fuel system as a culprit in performance anomalies. A faulty fuel system component—such as a leaky injector, a failing fuel pressure regulator, or a problem with the electronic control—can cause the engine to run improperly. This misfiring or irregular combustion creates abnormal forces and vibrations within the engine.

These irregular pulses and shocks can be transmitted through the crankshaft and ancillary drives, potentially manifesting as a slapping or rattling noise that mimics a loose timing chain. Furthermore, a rich fuel condition (excess fuel) can dilute engine oil, reducing its lubricating properties. Poor lubrication increases friction and wear on all internal components, including the timing chain, tensioners, and guides, potentially accelerating their failure. As owner gordoni pointed out regarding engine management, "The ECU is a computer that manages a bunch of systems that used to be purely mechanical. Stuff like spark timing, fuel to air ratio, fuel pressure, etc." A fault here can disrupt the precise harmony of engine operation.

How to Diagnose

Accurate diagnosis is essential to avoid unnecessary engine disassembly. Begin by verifying the symptoms. With the engine cold and in a quiet environment, listen carefully for the source of the noise. Use a mechanic’s stethoscope or a long screwdriver (placed carefully against components, NOT near moving belts) to isolate the sound. Check if the noise is coming from the front cover area (timing chain) versus the top of the engine (valvetrain) or accessory belt area.

The next critical step is to scan for diagnostic trouble codes (DTCs) using an OBD-II scanner capable of reading manufacturer-specific codes for the 2020 Corvette. Codes related to fuel trim (P0171, P0172), misfires, or cam/crank correlation are significant. Simultaneously, use a professional scan tool or advanced code reader to monitor live data. Pay close attention to long-term and short-term fuel trims, camshaft position sensor data, and engine oil pressure. Fuel trims significantly deviating from zero (±10%) indicate a fuel system problem.

Perform a visual and physical inspection. Check for any visible fuel leaks, especially around fuel rails and injectors. Inspect the engine oil level and condition; fuel-diluted oil will often smell strongly of gasoline and be thinner than normal. Check for oil leaks from the front timing cover. Finally, as a test, you can carefully remove the accessory drive belt and run the engine for a very short period (no more than 30-60 seconds) to rule out noise from alternators, tensioners, or the A/C compressor. If the slapping noise persists with the belt off, the issue is internal.

Step-by-Step Fix

If diagnosis confirms a fuel system issue as the primary cause, follow this repair path before considering timing chain replacement.

Step 1: Safety First & Preparation. Disconnect the negative battery terminal. Relieve the fuel system pressure by locating the fuel pump fuse or relay in the under-hood fuse block, starting the engine, and letting it stall. Crank it for a few more seconds to ensure pressure is bled. Have a fire extinguisher nearby and work in a well-ventilated area.

Step 2: Address the Fuel System Fault. Based on your diagnostic data, replace the faulty component. This is often a fuel injector. Remove the intake manifold assembly to access the fuel rails and injectors. Replace the suspect injector(s) with new, OEM-spec units. Always replace the injector seals. If fuel pressure is the issue, test the pressure at the rail with a gauge. Replace the fuel pressure regulator or fuel pump module as indicated by your tests. As one owner shared regarding procedures, "I recommend the procedure in that TSB; but with one caveat: read it thoroughly before committing. But, if you either cannot or will not adhere to the recipe & required timing schedule, Just Don't do it."

Step 3: Inspect Related Components. While you have access, inspect the spark plugs and ignition coils on the affected cylinder(s). Fouled plugs from a rich condition should be replaced. Check for any vacuum leaks on the intake manifold that could have contributed to the problem.

Step 4: Reassemble and Reset. Reinstall the intake manifold with new gaskets. Reconnect all electrical connectors, fuel lines, and vacuum hoses. Reconnect the battery.

Step 5: Prime and Test. Turn the ignition to the "ON" position (without starting) for several seconds to prime the fuel system. Listen for the pump to pressurize the rail. Start the engine and check immediately for any fuel leaks. Use your scan tool to clear all diagnostic trouble codes and monitor fuel trims as the engine idles and reaches operating temperature. The noise related to the misfire should be gone.

Step 6: If Noise Persists: Timing Chain Inspection. If the slapping noise remains after conclusively fixing the fuel issue, internal engine inspection is required. This involves removing the front timing cover—a major job on this vehicle that often requires engine support and removal of the front subframe and accessories. Inspect the timing chain for stretch (compare to a new chain), and check the plastic guides for wear or breakage and the hydraulic tensioner for proper operation. Replace the entire timing chain kit, including chain, guides, tensioner, and all related seals and gaskets.

Parts and Tools Needed

• For Fuel System Repair:
  • Fuel Injector (OEM recommended, part number specific to cylinder)
  • Fuel Injector Seal Kit
  • Intake Manifold Gasket Set
  • Spark Plugs (set of 8, OEM spec)
  • Tools: OBD-II Scanner with live data, Fuel Pressure Test Kit, Basic Mechanic's Tool Set (sockets, ratchets, torx bits), Torque Wrench, Fuel Line Disconnect Tools, Mechanic's Stethoscope.
• For Timing Chain Replacement (if necessary):
  • Complete Timing Chain Kit (includes chain, guide(s), tensioner, and likely front crankshaft seal)
  • Timing Cover Gasket Set
  • Engine Oil & Filter
  • Coolant
  • Additional Tools: Engine Support Bar, Floor Jack and Jack Stands, Harmonic Balancer Puller, Torque Angle Gauge, Dial Indicator (for checking cam timing).

Real Owner Costs

Costs vary dramatically based on the root cause and who does the work.

• DIY Fuel Injector Replacement: The cost is primarily parts. A single OEM fuel injector can range from $150 to $250. A full set of spark plugs adds $80-$120. With gaskets and seals, a DIY repair for a single bad injector typically costs $300 - $500 in parts. No labor cost.
• Professional Fuel System Repair: A dealership or specialist shop will charge 3-5 hours of labor for diagnosis and injector replacement. At $150-$200/hour, labor adds $450-$1000. Total bill for a single injector job often falls between $800 and $1,500.
• Professional Timing Chain Replacement: This is a major labor-intensive procedure. Owners report that just the diagnosis to confirm the need can cost $200-$400. The repair itself can easily take 15-20+ hours of book time. Parts (chain kit, gaskets, fluids) may cost $500-$800. Total costs from professional shops for a timing chain job on a high-performance engine like the Corvette's can range from $3,000 to over $5,000, depending on shop rates and whether any additional components are found to be damaged.

Prevention

Preventing issues that stress the timing chain starts with addressing root causes. Maintain a healthy fuel system by using Top Tier detergent gasoline and replacing fuel filters at the manufacturer's recommended intervals. Address any check engine lights immediately, especially those related to fuel trim or misfires, to prevent prolonged poor combustion. Adhere strictly to the recommended oil change intervals using the correct viscosity and quality of oil specified for your Corvette; clean oil is the lifeblood of the timing chain tensioner. As owner spinkick noted regarding general engine care, "getting your oil up to temp also has benefits for short distance drives where the motor never gets up to temp to boil off moisture in all the components, which is a huge source of wear." Avoid aggressive modifications that alter engine management without proper supporting hardware and tuning. As discussed by owners gordoni and smitty2919, non-OEM engine controls can introduce risk. smitty2919 clarified, "Manipulating a tune is just a software/program change but still resides within the OEM quality electronic hardware."

What Owners Say

Real experiences from CHEVROLET owners:

Success Stories

"When I pulled the bell housing and trans, I realized I had the incorrect flywheel. It would have worked, but on EBay there was a NOS correct 11” flywheel with the correct date for a decent price." — Tuna Joe (source)

"It would have worked, but on EBay there was a NOS correct 11” flywheel with the correct date for a decent price. Painted the bell housing, harmonic balancer, timing chain cover Bought a McLeod clutch and pressure plate." — Tuna Joe (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)

Pro Tips from Owners

💡 "If a tech follows the directions and suffers a component failure; chances are that component was already on its last legs. I recommend the procedure in that TSB; but with one caveat: read it thoroughly before committing But, if you either cannot or will not adhere to the recipe & required timing schedule, Just Don't do it." — Rebelyell (source)

💡 "I recommend the procedure in that TSB; but with one caveat: read it thoroughly before committing But, if you either cannot or will not adhere to the recipe & required timing schedule, Just Don't do it." — Rebelyell (source)

FAQ

Q: How long does it take to fix a fuel-related engine noise? A: If the issue is a single faulty fuel injector, a competent DIYer with the right tools can complete the diagnosis and replacement in a full day (6-8 hours), including intake manifold removal and reassembly. A professional shop would typically book 3-5 hours for this job.

Q: Can I drive my Corvette with a slapping or ticking noise? A: It is strongly not recommended. A noise indicative of a fuel system misfire can damage the catalytic converter from unburned fuel. If the noise is indeed from a failing timing component, continued driving risks severe engine damage, including bent valves if the chain skips time. The vehicle should be towed to a repair facility.

Q: Is a timing chain issue common on the 2020 Corvette (C8)? A: Based on available owner data, widespread timing chain failures are not a common reported issue for the C8 Corvette. The LT2 engine is relatively new but builds on a proven GM V8 architecture. Most unusual engine noises at low mileage are more likely related to accessory drives, the fuel system, or other ancillary components rather than the timing chain itself.

Q: DIY vs mechanic – what's recommended for this kind of problem? A: Diagnosing and repairing a fuel system fault like an injector is within the realm of an advanced DIYer who is comfortable working with fuel systems, intake manifolds, and following torque procedures. However, if the diagnosis points to an internal timing chain problem, the repair escalates significantly in complexity, requiring an engine support bar, special tools, and meticulous timing procedure adherence. For the timing chain job, most owners should seek a qualified professional. As an owner wisely advised, "if you either cannot or will not adhere to the recipe & required timing schedule, Just Don't do it."

Q: Could aftermarket parts cause problems that lead to these symptoms? A: Yes, absolutely. Owners express caution about non-OEM engine management components. As gordoni stated regarding aftermarket throttle controllers, "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 an OEM does." Using incorrect or low-quality fuel system parts can directly cause the performance issues that lead to concerning symptoms.

Q: What's the first thing I should check if I smell gas and hear a noise? A: Your first action should be to not start the engine again due to the fire hazard. Visually inspect the engine bay for any signs of fresh fuel leaks, particularly around the fuel rails on top of the engine. Then, have the vehicle towed to a technician who can safely diagnose it with a fuel pressure test and a scan tool to read live data and codes.