Arin@APR
GOLFMK7 Official Sponsor
I would like to start off by saying most people here have GTIs and we have not seen this issue on the GTI. Mainly we've seen the issue on GLI, Passat and CC engines with the new MED17.5.2 ECU. However, if you continue reading, you'll see the ECU has no bearing on the issue as originally speculated.
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Background:
Recently it has come to APR’s attention some 2.0 TSI EA888 vehicles equipped with K04 turbochargers and APR K04 software are experiencing misfires in the upper RPM range. Documented cases primarily exist on newer MK6 GLIs, CCs and Passats with MED 17.5.2 ECUs. However, some customers with nearly identical setups and identical software on these same platforms and others are not experiencing issues.
Diagnosis:
APR’s Engineers have spent countless hours diagnosing vehicles through both hardware and software analysis. Ultimately it was discovered that vehicles experiencing misfires were equipped with weaker exhaust valve springs from the factory. In fact, these weaker springs show roughly 10% less stiffness as shown on a spring dynamometer. These vehicles have identical Engine codes and exhaust valve part numbers as those with the proper valves. Unfortunately VW’s dealership parts system (ETKA) does not indicate a part change. Furthermore, APR has had a test vehicle in house for over a month with this issue. The issue was repeatable by anyone who drove the car. Since changing the springs to the appropriate stiffness the car has not experienced a single misfire on the production V2.0 calibration.
The photo below illustrates known good vs known bad factory valve springs.
The issue occurs when exhaust backpressure (coupled with the natural forces in a valve train) is high enough to cause the exhaust valves to stay open during the intake stroke. During this time, the intake valves are open and exhaust pressure is flowing back through the intake and into the intake manifold. In doing so, data will show a false rise in boost pressure and a corresponding drop in mass airflow. The car will then cease to accelerate, will eventually blink the Check Engine Light, disable the cylinder and throw the car into limp mode with a fault code for misfires.
In all cases we’ve seen these problems will not exist at stock output levels, or even at Stage 1 or 2 power levels due to lower exhaust backpressure. Furthermore, Stage 3 and 3+ vehicles are not experiencing these issues to date. This may sounds odd but the reason is simple. Stage 3 consists of a significantly larger manifold, turbine wheel, and wastegate therefore reducing the backpressure one would see with a high output K04.
The issues these vehicles have faced are very similar to one existing on some Audi S3 and TTS vehicles in the past. Ultimately it was determined by Audi the valve springs were weak enough to cause issues even on completely stock vehicles, so Audi released a Technical Service Bulletin (TSB) advising dealerships how to replace the problematic parts.
Solutions:
The primary solution to this issue is to replace the valve springs with a set of higher rated springs. The problematic vehicle we diagnosed in house received new valve springs and the issue completely disappeared with NO changes to the existing APR K04 MED17.5.2 software.
A secondary workaround to this issue is a software file that reduces engine output in the upper RPM range ultimately reducing back pressure. Peak torque remains consistent between the old and new software so despite having lower output, the vehicle still feels fast. This software can be made available upon request.
Home Diagnosis:
We are not stating that ALL misfires on every K04 car are caused by exhaust valve spring issues. As you all know, there are many possible sources for engine misfire. Some examples include: bad coil packs, fouled spark plugs, faulty fuel delivery systems, etc. This failure mode happens in a specific way that typically involves having misfire that is localized to Cylinder #3 (sometimes Cylinder #2) in the upper RPM band. The car will typically cease to accelerate once the problem is encountered.
Before concluding you may have weak exhaust valve springs, you should have already diagnosed the car through Vag-Com logging, swapping coil packs, swapping spark plugs, and maybe even changing the injector. Instructions for logging a vehicle using Vag-Com can be found here: http://www.goapr.com/support/datalogging.php
To check what valve springs you have, you can remove the PCV:
And attempt to inspect the color bands on the exhaust valve springs.
Please refer to the image above for known good and bad valve spring color bands.
Thank you for your patience during our diagnosis and Go APR!
-Arin
-------
Background:
Recently it has come to APR’s attention some 2.0 TSI EA888 vehicles equipped with K04 turbochargers and APR K04 software are experiencing misfires in the upper RPM range. Documented cases primarily exist on newer MK6 GLIs, CCs and Passats with MED 17.5.2 ECUs. However, some customers with nearly identical setups and identical software on these same platforms and others are not experiencing issues.
Diagnosis:
APR’s Engineers have spent countless hours diagnosing vehicles through both hardware and software analysis. Ultimately it was discovered that vehicles experiencing misfires were equipped with weaker exhaust valve springs from the factory. In fact, these weaker springs show roughly 10% less stiffness as shown on a spring dynamometer. These vehicles have identical Engine codes and exhaust valve part numbers as those with the proper valves. Unfortunately VW’s dealership parts system (ETKA) does not indicate a part change. Furthermore, APR has had a test vehicle in house for over a month with this issue. The issue was repeatable by anyone who drove the car. Since changing the springs to the appropriate stiffness the car has not experienced a single misfire on the production V2.0 calibration.
The photo below illustrates known good vs known bad factory valve springs.
The issue occurs when exhaust backpressure (coupled with the natural forces in a valve train) is high enough to cause the exhaust valves to stay open during the intake stroke. During this time, the intake valves are open and exhaust pressure is flowing back through the intake and into the intake manifold. In doing so, data will show a false rise in boost pressure and a corresponding drop in mass airflow. The car will then cease to accelerate, will eventually blink the Check Engine Light, disable the cylinder and throw the car into limp mode with a fault code for misfires.
In all cases we’ve seen these problems will not exist at stock output levels, or even at Stage 1 or 2 power levels due to lower exhaust backpressure. Furthermore, Stage 3 and 3+ vehicles are not experiencing these issues to date. This may sounds odd but the reason is simple. Stage 3 consists of a significantly larger manifold, turbine wheel, and wastegate therefore reducing the backpressure one would see with a high output K04.
The issues these vehicles have faced are very similar to one existing on some Audi S3 and TTS vehicles in the past. Ultimately it was determined by Audi the valve springs were weak enough to cause issues even on completely stock vehicles, so Audi released a Technical Service Bulletin (TSB) advising dealerships how to replace the problematic parts.
Solutions:
The primary solution to this issue is to replace the valve springs with a set of higher rated springs. The problematic vehicle we diagnosed in house received new valve springs and the issue completely disappeared with NO changes to the existing APR K04 MED17.5.2 software.
A secondary workaround to this issue is a software file that reduces engine output in the upper RPM range ultimately reducing back pressure. Peak torque remains consistent between the old and new software so despite having lower output, the vehicle still feels fast. This software can be made available upon request.
Home Diagnosis:
We are not stating that ALL misfires on every K04 car are caused by exhaust valve spring issues. As you all know, there are many possible sources for engine misfire. Some examples include: bad coil packs, fouled spark plugs, faulty fuel delivery systems, etc. This failure mode happens in a specific way that typically involves having misfire that is localized to Cylinder #3 (sometimes Cylinder #2) in the upper RPM band. The car will typically cease to accelerate once the problem is encountered.
Before concluding you may have weak exhaust valve springs, you should have already diagnosed the car through Vag-Com logging, swapping coil packs, swapping spark plugs, and maybe even changing the injector. Instructions for logging a vehicle using Vag-Com can be found here: http://www.goapr.com/support/datalogging.php
To check what valve springs you have, you can remove the PCV:
And attempt to inspect the color bands on the exhaust valve springs.
Please refer to the image above for known good and bad valve spring color bands.
Thank you for your patience during our diagnosis and Go APR!
-Arin
