The Audi S4 debuted the 4.2-liter V8 40-valve engine in 2003. There are 40 valves in this engine, distributed across its quad cam, 90-degree, V8 cylinders. Cast aluminum is used for the block and cylinder heads, while the crankshaft is built of forged steel. Despite being replaced by the 3.0L V6 FSI in 2008, Audi continued to utilize the engine until 2010.

The 4.2 V8 was recognized as one of Ward’s 10 Best Audi Engines for 2004 and 2005. Despite the engine’s popularity, it was eventually replaced with a smaller, more fuel-efficient V6 with forced induction because of its massive V8 footprint and low gas efficiency.

Audis with the 4.2-liter V8 engine

• 2002-2010 Audi D3 A8
• 2003-2005 Audi B6 S4
• 2002-2005 Audi C5 A6
• 2004-2006 Audi C6 A6
• 2004-2008 Audi B7 S4
• 2003-2010 Volkswagen Phaeton

Audi 4.2 V8 40v vs. 32v FSI

A 32-valve, redesigned 4.2L V8 was produced by Audi beginning in 2005. The 32v was based on the 40v architecture, although it has significant improvements over its predecessor. These include a redesigned  cylinder heads, oil cooler system,crankshaft, electronic control unit (ECU), rods and pistons, intake and exhaust system. During the years 2005-2011, the 32v version was standard on high-end vehicles including the R8, RS4, Q7, A6, and A8.

Audi also manufactured a 40v V8 before this model from 1999 to 2002, only to add extra complexity. They may all seem the same, but these engines all perform extremely differently.

The 4.2 V8 40v variant seen in the aforementioned vehicles is susceptible to the frequent problems we discuss here

Problems with the Audi 4.2 V8 engine

• Broken Timing Chain
• Collecting of Carbon
• Broken Solenoid Causing VVT/Vanos
• Broken Ignition Coil
• Linkage Arms for the Intake Manifold

Timing chain failure in a V8 engine

The intake and exhaust valves of the engine are opened and closed by the timing chain, which links the crankshaft and camshaft. The chain itself, guides, and a hydraulic tensioner are all used in this system to maintain the chain taut and prevent slack from developing. A timing chain cover, which is bolted to the engine block, shields the chain from debris and allows oil to reach it for lubrication.

Many things may cause the timing chains of a 4.2 V8 engine to break. The chains, for one, will eventually wear out and need replacement. However, not changing the oil regularly or letting the engine get too hot might shorten the chain’s useful life.

Plastic is used for the chain guides. They are constantly being shaken and heated up due of their proximity to the block. In extreme cases, this might lead to the plastic guides cracking. The chains may also skip teeth due to slack caused by faulty tensioners.

The 4.2 V8’s timing chains commonly break before the 100,000-mile mark and have even broken before 50,000 miles.

There are a few telltale signs of a broken timing chain in a V8 engine

• An issue with a misfiring cylinder
• The engine codes are P1340 and 17748
• Noises may be heard coming from the engine
• Limp mode

This diagnostic guide for timing chain failure will fill you in on the specifics. Timing chains often do not break down all at once. They begin to extend a little at first and keep on stretching as time goes on. However, if the guides or tensioners fail, the breakdown is more likely to be catastrophic.

Whenever the timing chain “fails,” the cam & crank gears will begin to skip teeth. A significant number of misfires will result from the engine timing being thrown off by this. The internal engine may be severely damaged if the chains skip too many teeth, sending the valves slamming into the pistons.

Replacing the Timing Chain

Audi 4.2 V8s are notoriously unreliable due to frequent timing chain breakdown. However, this is only one of several issues that contribute to the engine’s poor reputation.

Audi 4.2 V8s are unusual in that they put their timing chain on the rear of the engine, when in other vehicles it would be found on the front. Therefore, the whole engine must be removed, and hundreds of hours spent laboring are required to replace its timing chain.

Plus, the actual components are pricey; a whole timing chain replacement kit may set you back more than $4,000. The labor costs alone would make this a costly replacement that would cost over $8,000.

Keep your oil changed regularly to avoid a timing chain breakdown. Regardless of the manufacturer’s suggested oil change frequency, we advise doing this maintenance every 5,000 miles.

2. The accumulation of carbon in a 4.2-liter V8 engine

Direct injection powers the 4.2-liter V8. Gasoline injectors in direct injection engines atomize the fuel before spraying it into the engine cylinder. Port injection is an alternative to direct injection. Port injection works by spraying gasoline into the intake manifold; the fuel then passes through the manifold and the valves before entering the combustion chamber.

Using port injection, the gasoline flows into the manifold and valves, cleaning them of any residue or debris that may have accumulated. No highly pressured gasoline is going through the manifold & valves to assist clean them out when direct injection is used.

Carbon buildup is the outcome, which coats the valves & intake manifold with sludge. Carbon deposits left behind after combustion can eventually jam the engine’s air intake and valves. This hinders ventilation and may cause numerous performance difficulties.

Signs of Carbon Buildup

• An issue with a misfiring cylinde
• Hard starting and idling
• Overall, the performance was poor
• Slow starting speed
• Difficulty in starting the engine
• A decrease in fuel efficiency
• Cleaning Up the Carbon Smog

Over time, carbon accumulates. These indications (misfires, harsh idling, etc.) may go unnoticed since performance declines gradually over time. Carbon buildup won’t create any severe engine problems, but it’s still a good idea to clean the valves & intake ports every 80,000-110,000 miles.

A significant quantity of residue will have accumulated on the engine’s valves and ports by the time you reach this mileage. In terms of performance, cleaning them will undoubtedly revive the automobile and eliminate any sluggishness.

Walnut blasting is the most effective method for eliminating carbon accumulation. Walnut blasting involves using a shop vac to force a large quantity of finely ground walnut shells into the engine’s valves and intake ports, removing any residue that has built up there.

Audi 4.2 V8: Avoiding Carbon Buildup

Although carbon accumulation cannot be eliminated entirely, it may be mitigated by a combination of measures:

• Every 5,000 miles, you should have the oil and filter changed
• Be sure to set up an oil catch container
• The fuel injectors should be cleaned using ethanol
• Only gasoline with a minimum octane rating of 93 should be used
• Occasionally spend 20 or 30 minutes cruising at high revs

3. Broken VVT in a 4.2-liter V8.

Variable valve timing, sometimes known as VVT or Vanos, is a feature of Audi’s V8 engines. The camshaft’s position may be adjusted for more accurate exhaust and intake valve timing thanks to a system variable.

In order to adjust the camshaft timing, the system employs a variable valve timing solenoid that is activated by oil pressures. These solenoids are prone to failure due to buildup of muck, which in turn may affect engine performance and timing.

Signs of a faulty VVT solenoid

• Hard starting and idling
• Weakness in the low-end range
• A lot of misfires have been happening recently
• The fuel economy has deteriorated
• Problems starting from cold temperatures
• Acceleration causes engine to enter limp state

Solenoid Replacement Options

Even while you can clean your solenoids by pulling them out, this is often just a stopgap measure. Every 70,000 to 80,000 miles, your solenoids will fail and need to be replaced for optimal performance. Inadequate solenoids can be driven on for a while, but ultimately they will get too clogged to allow for even moderate acceleration.

4. Audi 4.2L Ignition Coil Problems

There must be an electrical current for the spark plug to ignite. Ignition coils provide the power they need. Connecting to the car’s battery system, ignition coils sit above the spark plug. The spark plugs get power from the battery via the ignition coils, which then discharges the energy into the combustion chamber.

The ignition coils in the 4.2 V8 are particularly vulnerable to overheating because to their location inside the cylinder. Electrical components and high temperatures do not mix well. Over time, the coils wear out and fail because of the engine’s heat. This occurs often in any internal combustion engine that makes use of ignition coils.

After 50,000 to 70,000 miles, coils often break. Tuning or using bolt-on modifications increases the likelihood of failure. There is, however, no way to guarantee success. Fortunately, failures seldom occur in clusters but rather on an individual basis. As a result, if any of them should ever break, you won’t need to replace the whole thing at once, but rather just the bad one.

The Signs of a Bad Ignition Coil

• An issue with a misfiring cylinder
• Indicator light for check engine
• Lessening of strength
• Difficulty in starting
• Hard starting and idling
• Idle speed

Maintenance: Swap out the Ignition Coil

DIY repairs on a 4.2 V8 engine are rather simple. While it is true that replacing all 8 ignition coils would not break the bank, it will still be an expensive endeavor. Some individuals want to replace everything at once to make sure the automobile is running at peak efficiency, while others prefer to do it in stages.

Because of the inevitable deterioration of these components over time, you may have performance concerns if you mix a few freshly manufactured coils with a few older coils in operation. If you’re going to replace your 8 ignition coils, you may as well replace your spark plugs while you’re at it.

5. The linkage arm on the 4.2-liter V8 intake manifold broke

There is a variable intake manifold on the 4.2-liter V8 engine. Variable manifolds have two channels, as opposed to the single channel used by conventional manifolds to provide air to the cylinders. An actuator operates a flap that directs air flow via a long or short route, depending on which passage is being used.

Two arms of the manifold linkage system keep the flap in place. The firm that made these linkage arms used plastic. Their low quality of construction makes them prone to breaking and snapping. When the actuator flap’s linkage arms wear down, it stops working as intended, causing a host of performance problems.

Signs of a Broken Link Arm

• Misfires
• Poor efficiency
• Lack of promptness while starting to speed up
• Poorer gas mileage

Replacing Missing Link Arms

Do not use oem arms to repair the linkage. To begin, the dealership won’t sell you just the linkage arms—which would save you over $400—but instead will only sell you the “complete” kit. If one arm fails, you may easily purchase a replacement and switch it out without having to replace the whole actuator.

Replace your current linkage arms with metal ones, like the Gruven Linkage Arms, that are made from steel and will last forever.

Reliability of the Audi 4.2 V8 Engine

Audi’s 4.2L V8 has a poor reputation for dependability because of the frequency with which its timing chain fails and the high price of replacing its components. Using the right oil, preventing oil levels from dropping too low, and replacing the oil per 5,000 miles rather than at the prescribed intervals will help prevent a lot of the problems that come up with these timing chains.

Aside from problems with the timing chain, the 4.2-liter V8 engine has few other potential weak points that might cause it to fail completely. The majority of the other typical problems are often inexpensive maintenance items that are fixed with little effort and cost. Transmission failure, though, is a significant problem that isn’t connected to the engine. Transmissions paired with 4.2-liter V8 engines often develop issues after 120,000 miles.

There are a variety of reasonably priced Audis on the market right now, including the S4 and others equipped with the 4.2-liter V8. If you can’t afford and aren’t willing to pay to have the timing chain replaced on your V8 Audi, you’re overpaying. The likelihood of the timing chain breaking increases with the age and mileage of these engines, so although it may be less of a problem on a limited mileage and highly well-maintained Audi, it is still something to keep in mind.

The 4.2L V8 costs a lot to maintain as a whole. Unless you’re willing to spend a lot of money on maintenance, I wouldn’t count on it lasting more than 120k miles.