Audi’s 4.2L V8 40v engine was released in 2003 in the Audi S4. It is a quad cam, 90-degree V8 with 5 valves per cylinder, totaling 40 valves. The block and heads are made of cast aluminum with a forged steel crank. The engine was used by Audi until 2010, although it had begun being phased out in favor of the 3.0L Supercharged V6 FSI engine as early as 2008.
The 4.2 V8 won Ward’s 10 Best Engines two years in a row, in 2004 and 2005. Despite the success of the engine, the large V8 footprint and associated poor gas mileage led to the engine being phased out in favor of a smaller, more fuel efficient V6 coupled with forced induction.
Audi’s that use the 4.2 V8
- 2003-2005 Audi B6 S4
- 2004-2008 Audi B7 S4
- 2002-2005 Audi C5 A6
- 2004-2006 Audi C6 A6
- 2002-2010 Audi D3 A8
- 2003-2010 Volkswagen Phaeton
Audi 4.2 V8 40v vs. 32v FSI
In 2005 Audi built a revised, 32-valve version of the 4.2L V8. While the 32v was built off of the 40v platform, it received numerous upgrades including a new crankshaft, rods and pistons, cylinder heads, oil cooler system, intake and exhaust system, and ECU. The 32v version was used in premium cars such as the R8, RS4, Q7, and A6 and A8 models from 2005 through 2011.
To confuse matters more, Audi produced a predecessor 40v V8 from 1999 until 2002. While all these engines are similar in design they are very different engines.
The common problems we mention in this post are applicable to the 40v version of the 4.2 V8 that are fitted into the cars mentioned above.
Audi 4.2 V8 Engine Problems
- Timing Chain Failure
- Carbon Buildup
- VVT/Vanos Solenoid Failure
- Ignition Coil Failure
- Intake Manifold Linkage Arms
1. 4.2 V8 Timing Chain Failure
The timing chain connects the crankshaft and camshaft together and controls the opening and closing of the engines intake and exhaust valves. In addition to the chain itself, this system also uses guides to keep the chain in place and a hydraulic tensioner to keep slack out of the chain. The chain is protected within a timing chain cover that bolts up to the block to protect it from road dirt and to lubricate it with oil.
The 4.2 V8 timing chains fail for a number of reasons. First off, the chains naturally stretch over time and need to be replaced. While they generally should last the life of the car, infrequent oil changes and engine overheating can cause the chain to stretch more quickly than normal.
The chain guides are made of plastic. Because they are right up near the block they are subject to constant vibration and high temperatures. This can cause the plastic guides to break. Additionally, the tensioners can fail which causes slack in the chains which can lead them to jump teeth.
Timing chains on the 4.2 V8 frequently fail before the 100,000 mile mark and have failed as early as 50,000 miles.
4.2 V8 Timing Chain Failure Symptoms
- Cylinder misfires
- P1340, 17748 engine codes
- Rattling from the engine
- Limp mode
For more details, you can check out this guide on diagnosing timing chain failure. Timing chains don’t usually fail immediately. They usually start to stretch a small amount and continue to stretch over time. However, guides and tensioners breaking can cause more imminent failure.
When the timing chain “fails” it usually starts jumping teeth on the cam and crank gears. This throws off engine timing and will lead to a lot of misfires. If the chains jump too many teeth it can send the valves crashing into the pistons causing catastrophic internal engine damage.
Timing Chain Replacement Options
The Audi 4.2 V8 gets a very bad rap for reliability because of timing chain failure. While this is a very common problem, it’s only part of the reason the engine has a bad reputation.
While most cars have their timing chain mounted on the front of the engine block, the Audi 4.2 V8 actually has it located on the back side of the engine. Therefore, to replace the timing chain you have to pull the whole engine, resulting in dozens of hours of labor.
Additionally, the parts themselves are not cheap, with a full timing chain repair kit costing over $4,000. Once you tack on labor you are looking at an $8,000+ replacement job.
To prevent timing chain failure make sure you change your oil frequently. We recommend doing it every 5,000 miles regardless of the factory oil change intervals.
2. 4.2 V8 Carbon Buildup
The 4.2 V8 is a direct-injected engine. Direct injection engines use fuel injectors to spray fuel directly into the combustion chamber. The alternative to direct injection is port injection. With port injection the fuel is sprayed into the intake manifold and then travels through the intake manifold and valves into the combustion chamber.
When you use port injection, the fuel traveling through the manifold and valves helps clean them from built up gunk. However, when you use direct injection, the fuel is sprayed directly into the combustion chamber so no highly pressurized gasoline is passing through the manifold and valves to help clean them out.
The result is the valves and intake manifold getting coated in gunk, called carbon buildup. These left over carbon deposits will slowly clog up the intake system and valves. This restricts air flow and can lead to various performance issues.
Carbon Buildup Symptoms
- Cylinder misfires
- Rough idling
- Poor overall performance
- Sluggish acceleration
- Hard starts
- Worse gas mileage
Removing Carbon Buildup
Carbon buildup happens over time. These symptoms a lot of times aren’t noticeable (except misfires and rough idling) since the performance tends to deteriorate slowly over time. While carbon buildup isn’t going to cause any serious engine problems we still recommend cleaning the valves and intake ports every 80,000-100,00 miles.
By the time you hit this mileage there will be a good amount of buildup on the valves and ports. Cleaning them will definitely bring the car back to life a bit from a performance perspective and get rid of any sluggish performance.
The best route for removing carbon buildup is through a process called walnut blasting. Walnut blasting uses a shop vac to blow a bunch of small walnut shells through the valves and intake ports to clean away all of the buildup.
Preventing Carbon Buildup – Audi 4.2 V8
While there is no way to completely remove carbon buildup, you can prevent some buildup and slow down how quickly it accumulates.
- Change your oil and filter every 5,000 miles
- Install an oil catch can
- Use ethanol fuel injector cleaner
- Use 93 octane fuel or higher only
- Drive on the highway at high rpm’s for 20-30 minutes from time to time
3. 4.2 V8 Variable Valve Timing Failure
Audi’s V8 engines use variable valve timing technology, commonly referred to as VVT or Vanos. The system variable alters the position of the camshaft, allowing for more precise intake and exhaust valve timing.
The system uses a VVT Solenoid which is actuated via oil pressures to control the camshaft timing. These solenoids frequently get clogged or gunked up which can cause them to fail and lead to performance and timing related engine issues.
VVT Solenoid Failure Symptoms
- Rough idling
- Loss of low range power
- Frequent misfires
- Decreased gas mileage
- Cold start issues
- Engine goes into limp mode during acceleration
Solenoid Replacement Options
While you can simply pull your solenoids and clean them, this is usually a bandaid fix. Solenoids will typically go bad every 70,000-80,000 miles and will need to be changed for optimal performance. You can drive on bad solenoids for a period of time but the solenoids will eventually become too gunked up and result in very decreased driveability.
4. Ignition Coil Failure – Audi 4.2L
For spark plugs to fire and create combustion, they need electricity. The electricity they get comes from ignition coils. Ignition coils mount onto the top of the spark plug and connect to the cars battery system. The ignition coils transfer the electrical current from the battery to the spark plugs, allowing the plugs to fire and create combustion.
Because the ignition coils sit within the cylinder of the 4.2 V8, they are subject to a lot of heat. Heat and electrical components do not usually go well together. The heat from the engine wears the coils down over time and causes them to fail. This is common for pretty much any engine that uses ignition coils.
Coils tend to fail every 50,000-70,000 miles. If you are tuned or running bolt-on modifications, then they usually fail a bit more frequently. Unfortunately, there really is no way to prevent failure. Fortunately, they do not tend to fail all at once but rather fail individually. Therefore, when they do fail you can replace them one at a time instead of having to buy a brand new set every time.
Ignition Coil Failure Symptoms
- Cylinder misfires
- Check engine light
- Decreased power
- Hard starts
- Rough idling
- Lack of acceleration
Ignition Coil Replacement
DIY replacement is pretty easy on the 4.2 V8. The ignition coils themselves are pretty cheap, although that adds up when you need to replace all 8 of them. A lot of people prefer to replace all of them at the same time to ensure that the car is performing at optimal levels.
These parts wear down naturally over time so running a handful of brand new coils with a handful of old coils can potentially create some noticeable performance issues. For less than $250 you can get all 8 ignition coils AND spark plugs so we generally recommend replacing them all together.
5. 4.2 V8 Intake Manifold Linkage Arm Failure
The 4.2L V8 has a variable intake manifold. While a traditional manifold just distributes air through one passageway to the cylinders, a variable manifold has two passages. There is a long passage and a short passage and an actuator that controls a flap that delivers air to either one of the passages.
The flap is held on by two manifold linkage arms. These linkage arms were manufactured out of plastic from the factory. They are very poorly manufactured and therefore snap and break very easily. When the linkage arms break, the actuator flap no longer functions properly which leads to various performance issues.
Linkage Arm Failure Symptoms
- Sluggish performance
- Hesitation during acceleration
- Worse fuel economy
Linkage Arm Replacement Options
Do not replace the linkage arms with OEM arms. First of all, the dealership will only sell you a “full” kit instead of just the linkage arms which is $400+. When the arms break you can simply buy replacement arms and swap them out without having to change the actuator and everything else.
Upgrade to metal linkage arms, such as the Gruven Linkage Arms, which are manufactured from steel and will never break.
Audi 4.2 V8 Reliability
Audi’s 4.2L V8 gets a bad reputation for reliability primarily because of the commonality of timing chain failure as well as the cost to replace the timing chain components. While these timing chains are a serious concern, most of the problems associated with them can be mitigated by always using the proper oil, making sure oil levels don’t get too low, and changing the oil every 5,000 miles instead of at the recommended interval levels.
Outside of the timing chain issues, the 4.2 V8 doesn’t many issues that can lead to catastrophic engine failure. Most of the other common problems are less expensive general maintenance items that can be taken care of easily and cheaply. However, one other noteworthy problem that isn’t engine related is transmission failure. The transmissions that go along with the 4.2L V8 usually start to become problematic around the 120,000 mile mark.
A lot of the S4’s and other Audi’s with the 4.2L V8 are pretty cheap nowadays. Don’t think you are getting a banging deal on a V8 Audi unless you can afford and are willing to pay for timing chain replacement. While it might be less of a concern on a low-mileage and very well maintained Audi, the chances of the timing chain failing are higher and higher as the mileage on these engines goes up.
Overall, the 4.2L V8 is an expensive car to maintain. I wouldn’t expect much more than 120k miles out of one before you have to start breaking out big dollars on repairs.