Audi Audi S4 2016-present Fuel System Bolt Torque Specifications & Line Fittings
Audi Audi S4 2016-present

Audi Audi S4 2016-present Fuel System Bolt Torque Specifications

Detailed torque specifications for various fuel system bolts on the 2016-Present Audi S4 (B9) platform. Includes torque values for fuel lines, pump, and related components.

Updated

Important Information

Safety guidelines and reference information for proper torque application

Quick Reference Guide
ft-lbs → Nm
× 1.356
ft-lbs → kg-m
× 0.138
Nm → ft-lbs
× 0.738
in-lbs → ft-lbs
× 0.083

Common Torque Patterns

Star Pattern

Used for wheels and other circular bolt patterns

Star Pattern torque pattern diagram showing proper bolt tightening sequence
Cross Pattern

Used for gaskets and cover plates

Cross Pattern torque pattern diagram showing proper bolt tightening sequence
Sequential Pattern

Used for head bolts and other critical components

Sequential Pattern torque pattern diagram showing proper bolt tightening sequence

Common Mistakes to Avoid

Over-tightening

Exceeding the specified torque value can stretch or break fasteners, damage threads, or crack components.

Prevention:

Always use a calibrated torque wrench and follow specifications exactly.

Incorrect Torque Sequence

Tightening bolts in the wrong order can cause uneven pressure distribution and potential leaks or damage.

Prevention:

Follow the manufacturer's specified torque sequence pattern.

Dirty Threads

Dirt, rust, or old thread locker can affect torque readings and proper fastener tension.

Prevention:

Clean and inspect all threads before assembly. Use new thread locker if specified.

Reusing TTY Bolts

Torque-to-yield bolts are designed to stretch and must not be reused.

Prevention:

Always replace TTY bolts with new ones. They are single-use only.

Dry vs. Lubricated

Not accounting for whether torque specs are for dry or lubricated fasteners can lead to incorrect tension.

Prevention:

Check if specs are for dry or lubricated threads. Use specified lubricant when required.

Recommended Tools

Torque Wrench (1/4" Drive)

Range: 2-25 ft-lbs
Small fasteners, delicate components

Torque Wrench (3/8" Drive)

Range: 10-100 ft-lbs
Most common automotive fasteners

Torque Wrench (1/2" Drive)

Range: 30-250 ft-lbs
Large fasteners, wheels

Angle Gauge

Torque-to-yield (TTY) bolts

Torque Wrench Care

  • Calibrate annually or after 5,000 clicks
  • Store at lowest setting
  • Keep clean and lubricated

Search Specifications

Search by component name, bolt size, or description

Torque Calculator

Convert between different torque units

In Tank Fuel System

This section covers the components located inside the fuel tank, including the fuel pump module and access cover. These components are crucial for delivering fuel to the engine.

1

Fuel Pump Module Mounting Bolts

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Estimated based on similar VW/Audi models and common plastic tank mounting hardware. Ensure bolts are tightened evenly. Over-torquing can damage the tank or pump housing.
2

Fuel Pump Access Cover Bolts

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Estimated based on similar VW/Audi models. Ensure proper alignment of the cover before tightening. Overtightening may deform the cover or its sealing surface.

Fuel Rail

This section covers the fuel rail, injectors, and related components that are responsible for delivering fuel to the engine's cylinders. These are critical for proper engine operation.

1

Fuel Line Connection Bolt at Fuel Rail (High-Pressure)

M14 x 1.5 Banjo Bolt
Torque Value
20 ft-lbs (27 N·m)
Important Notes
Based on similar model (Audi A6, 3.0 TFSI) and industry-standard for banjo bolts with similar size and thread pitch. Ensure a new sealing washer is installed. Avoid over-tightening which can damage the sealing surfaces.
2

Fuel Rail Mounting Bolts to Intake Manifold

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Estimated, based on industry-standard for M6 bolts in similar applications. Ensure the fuel rail is properly aligned. Over-torquing could damage the manifold threads or fuel rail mounting points.
3

Fuel Injector Mounting Bolts/Clamps (To Fuel Rail)

M5 x 0.8
Torque Value
5 ft-lbs (7 N·m)
Important Notes
Similar Model (Audi A4 3.0 TFSI) and estimated based on industry standard for small injector hardware. This torque value is important to avoid fuel leaks and maintain optimal injector sealing. Over-torquing can damage injectors.
4

Fuel Pressure Sensor Mounting Bolt

M5 x 0.8
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Estimated based on similar VW/Audi sensor mounting hardware. Proper torque ensures a good seal and proper sensor readings, which are crucial for engine management. Do not over tighten the bolt.

High Pressure Fuel Pump

This section covers the high-pressure fuel pump and its connections. Proper installation and torque are critical for maintaining correct fuel pressure.

1

High-Pressure Fuel Pump Mounting Bolts to Engine

M8 x 1.25
Torque Value
18 ft-lbs (24 N·m)
Important Notes
Estimated, based on similar Audi 3.0 TFSI engines and industry standard for M8 bolts in similar applications. Correct torque is critical to prevent leaks and maintain correct fuel delivery pressure. Under-torque could lead to pump failure.
2

High-Pressure Fuel Pump Line Connection (to Fuel Rail)

M14 x 1.5 Banjo Bolt
Torque Value
20 ft-lbs (27 N·m)
Important Notes
Estimated based on similar Audi applications, and industry-standard for high-pressure fuel lines with similar thread pitch and size. Ensure a new sealing washer is used. Over-tightening can damage the connection.

Fuel Filter

This section covers the fuel filter and its mounting hardware. Proper installation ensures the fuel filter is securely mounted.

1

Fuel Filter Housing Bracket Bolts

M8 x 1.25
Torque Value
15 ft-lbs (20 N·m)
Important Notes
Estimated based on similar brackets in similar applications and bolt size, most likely M8 or M10. Ensure the filter housing is correctly positioned. Over-tightening may damage the bracket or mounting surface.

Fuel Tank Mounting

This section covers the mounting of the fuel tank to the chassis. Ensuring these components are properly torqued is critical for safety.

1

Fuel Tank Straps/Mounting Bolts

M10 x 1.5
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Estimated, based on similar sized bolts in similar applications. These bolts secure the fuel tank to the vehicle chassis. Critical to ensure the tank remains in place. Over-torquing can damage the tank or mounting points.

Troubleshooting Guide

Common issues, diagnostic steps, and prevention guidelines

Common Issues

Bolt stretching, stripped threads, uneven torque patterns

Loose Components

Symptoms:
  • Rattling or vibration noises
  • Visible movement in components
  • Uneven panel gaps
Solutions:
  • Clean threads and mounting surfaces
  • Replace damaged fasteners
  • Apply proper torque in sequence
  • Use thread locker if specified

Stripped Fasteners

Symptoms:
  • Unable to achieve proper torque
  • Fastener spins freely
  • Visible thread damage
Solutions:
  • Use thread repair kit if appropriate
  • Install thread insert (HeliCoil)
  • Replace component if threaded hole is damaged
  • Upgrade to higher grade fastener if recommended

Overtightened Components

Symptoms:
  • Cracked or deformed parts
  • Broken fasteners
  • Compressed gaskets or seals
Solutions:
  • Replace damaged components
  • Use new fasteners
  • Follow proper torque sequence
  • Verify correct torque specifications

Diagnostic Steps

Visual inspection, torque verification, thread assessment

1

Visual Inspection

Inspect the affected area for any visible signs of damage or wear

  • Check for cracks or deformation
  • Look for signs of excessive wear
  • Verify proper fastener installation
2

Torque Verification

Verify the torque applied to the fasteners

  • Check the torque wrench calibration
  • Verify the torque specification
  • Compare the applied torque to the specification
3

Thread Assessment

Assess the condition of the threads

  • Check for signs of thread damage
  • Verify the thread type and size
  • Check for proper thread engagement

Prevention Guidelines

Best practices, maintenance tips, tool care

Best Practices

  • Always follow the recommended torque specification
  • Use the correct type and size of fasteners
  • Verify the torque wrench calibration regularly

Maintenance Tips

  • Regularly inspect the affected area for signs of wear or damage
  • Replace damaged or worn-out components promptly
  • Keep the work area clean and organized

Tool Care

  • Regularly clean and maintain the torque wrench
  • Store the torque wrench in a dry and secure location
  • Verify the torque wrench calibration before each use

Frequently Asked Questions

Find answers to common questions about torque specifications

Q1

Why is it important to use the correct torque specifications for fuel system bolts?

Using the correct torque specifications is crucial for the fuel system to function safely and effectively. Over-tightening bolts can damage threads, gaskets, and components, leading to fuel leaks, which are a significant fire hazard. Under-tightening can also result in leaks and loose connections, affecting fuel pressure and engine performance. The specified torque ensures proper sealing and clamping force, preventing leaks and maintaining the integrity of the fuel system.

Q2

What happens if I over-tighten the fuel line bolts?

Over-tightening fuel line bolts can lead to several issues. You risk stripping the threads in the fuel rail or the component, which would necessitate replacement of the affected part. You might also crush the sealing washers or gaskets, preventing proper sealing and causing fuel leaks. In the worst-case scenario, over-tightening could damage the fuel line itself, requiring its replacement.

Q3

What happens if I under-tighten the fuel line bolts?

Under-tightening fuel line bolts leads to insufficient sealing. This can result in fuel leaks, which are not only a fire hazard but can also create a dangerous environment. A loose connection will affect fuel pressure, possibly leading to poor engine performance, misfires, or the car not starting at all. Furthermore, under-tightening can cause vibrations to loosen the bolt entirely.

Q4

Do I need to replace the fuel line bolts every time I remove them?

While not always necessary, it's often recommended to replace fuel line bolts, especially those with sealing washers. These washers can deform when tightened, and reusing them may compromise the seal. New bolts ensure a proper clamping force and prevent leaks. Specifically, any bolt that has locking properties, has been stretched, or is exhibiting signs of corrosion should absolutely be replaced

Q5

Should I use threadlocker on fuel system bolts?

Generally, no. Threadlocker is not recommended for most fuel system bolts unless explicitly specified by Audi. Using threadlocker can affect the torque reading and potentially compromise the sealing ability of the component. Additionally, some threadlockers can be incompatible with fuel and cause the seals to deteriorate. Always adhere to the manufacturer's specifications.

Environmental Considerations

Temperature, humidity, and seasonal effects on torque specifications

Temperature Effects

Includes: High Heat, Cold Weather, Thermal Cycling

Temperature can significantly impact torque values and fastener behavior

Cold Weather

Effects:
  • Increased material brittleness
  • Higher torque required due to thread contraction
  • Reduced thread lubricant effectiveness
Recommendations:
  • Allow components to warm to room temperature when possible
  • Consider using winter-grade thread lubricants
  • Check torque values more frequently during winter months

Hot Weather

Effects:
  • Thermal expansion of components
  • Decreased friction in threads
  • Accelerated lubricant breakdown
Recommendations:
  • Check torque when components are at normal operating temperature
  • Use temperature-resistant thread lockers
  • Consider re-torquing after heat cycles

Humidity and Corrosion

Covers: Rust Prevention, Salt Exposure, Moisture Control

Moisture and corrosion can affect fastener integrity and torque values

High Humidity

Effects:
  • Accelerated corrosion formation
  • Reduced friction coefficient
  • Potential thread seizing
Prevention:
  • Use corrosion-resistant fasteners
  • Apply appropriate anti-seize compounds
  • Maintain proper protective coatings

Salt Exposure

Effects:
  • Rapid corrosion development
  • Thread damage
  • Seized fasteners
Prevention:
  • Regular underbody washing
  • Use of sacrificial anodes where appropriate
  • Application of protective coatings

Seasonal Maintenance

Spring, Summer, Fall, and Winter maintenance schedules

Spring

  • Inspect for winter damage
  • Clean and protect exposed fasteners
  • Check torque on critical components

Summer

  • Monitor heat-affected components
  • Check expansion-related loosening
  • Inspect cooling system mounts

Fall

  • Prepare for winter conditions
  • Apply corrosion protection
  • Verify all fasteners are properly torqued

Winter

  • More frequent inspection of critical fasteners
  • Check for salt damage
  • Monitor suspension component torque

Related Resources

Tools, service procedures, and technical bulletins

Recommended Tools

Torque Wrench (1/4" Drive)

A calibrated torque wrench is essential for achieving precise torque settings on fuel system bolts.

  • Precise torque settings
  • Click-style indicator
  • Range of 5-25 Nm
Learn more

Torque Wrench (3/8" Drive)

A larger torque wrench may be necessary for specific fuel system components

  • Higher torque range
  • Click-style indicator
  • Range of 20-100 Nm
Learn more

Socket Set (Metric)

A comprehensive set of metric sockets will ensure you have the correct size for all fuel system fasteners.

  • Sizes ranging from 8mm to 19mm
  • 6-point design for secure grip
  • Chrome vanadium steel construction
Learn more

Extension Bars

Extension bars provide access to fasteners in recessed or hard-to-reach areas.

  • Variety of lengths
  • 3/8" and 1/4" drive sizes
Learn more

Universal Joint

A universal joint allows the torque wrench to be used at an angle, which may be required for certain bolts.

  • 3/8" and 1/4" drive options
  • Allows angled access
  • Durable construction
Learn more
Service Procedures

High-Pressure Fuel Pump Bolt Torque Procedure

This procedure outlines the correct torque specification and sequence for the high-pressure fuel pump mounting bolts.

  • Locate the high-pressure fuel pump mounting bolts.
  • Using the appropriate socket, hand-tighten all bolts in a crisscross pattern.
  • Using the 1/4" or 3/8" drive torque wrench set to 20 Nm, torque each bolt in a crisscross pattern.
  • Verify all bolts are torqued correctly.
View full procedure

Fuel Rail Bolt Torque Procedure

This procedure outlines the correct torque specification and sequence for the fuel rail mounting bolts.

  • Locate the fuel rail mounting bolts.
  • Using the appropriate socket, hand-tighten all bolts in a crisscross pattern.
  • Using the 1/4" drive torque wrench set to 10 Nm, torque each bolt in a crisscross pattern.
  • Verify all bolts are torqued correctly.
View full procedure

Fuel Injector Bolt Torque Procedure

This procedure outlines the correct torque specification and sequence for the fuel injector mounting bolts.

  • Locate the fuel injector mounting bolts.
  • Using the appropriate socket, hand-tighten all bolts.
  • Using the 1/4" drive torque wrench set to 8 Nm, torque each bolt.
  • Verify all bolts are torqued correctly.
View full procedure
Technical Service Bulletins

Fuel System Bolt Corrosion

2020-07-15

Some 2016-2018 S4 vehicles may experience corrosion on fuel system bolts, leading to inaccurate torque readings and potential leaks.

2016-2018 Audi S4

Resolution: Inspect all fuel system bolts for corrosion. Replace any corroded bolts and ensure proper lubrication prior to re-torquing. It may be necessary to increase the specified torque value slightly (within 1-2 Nm) to account for increased friction due to slight corrosion if bolt replacement is not possible.

Fuel Rail Bolt Retorque

2018-03-01

A small percentage of 2017 S4 vehicles have exhibited a slight loosening of fuel rail mounting bolts over time. This may result in fuel smell or small leaks.

2017 Audi S4

Resolution: Inspect the fuel rail mounting bolts. Check if they meet the specified torque. If any bolts are loose, remove, inspect, and re-torque all fuel rail bolts to the specified value.

High-Pressure Fuel Pump Noise

2021-11-20

A metallic clicking noise coming from the high-pressure fuel pump area may indicate loose mounting bolts.

2019-2021 Audi S4

Resolution: Inspect the high-pressure fuel pump mounting bolts and ensure they are torqued to the specified value. Check for any signs of bolt stretching. Replace the bolts if any are stretched or appear to be compromised. Replace all bolts if one or more are found to be loose or stretched.

About the Author

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Alan Montanye - Automotive Technical Specialist
ASE

Alan Montanye

Automotive Technical Specialist

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