PSA: CCV Breather Hose for CSL Airbox Install on S54s Mid-2004 and Newer
A PSA for those installing a CSL airbox on an E46 M3 with production date mid-2004 or newer:
I have been attempting to resolve a surging, rough, misfiring idle for awhile now that manifests only with CSL airbox installed. The issue manifests with either an MSS54 with Alpha-N tune or an MSS54HP converted to CSL spec with genuine CSL software. The issue does not manifest with the OE US airbox running a MAF and stock software on the MSS54. The issue has all the symptoms of a post-ICV vacuum leak, but I have been unable for the life of me to find the leak.
While noodling the problem the other day, the solution hit me like a ton of bricks. The culprit was indeed a post-ICV vacuum leak. An especially sneaky one.
I have a late S54 motor with a production date later than mid-2004, including all of the quality-of-life improvements BMW made.
On S54s with a production date earlier than mid-2004, the crankcase breather setup was comprised of a simple straight hose between the crankcase CCV port and the intake plenum. This hose is very similar to the hose included on the CSL. The hose is part number 2 in the following diagram courtesy of RealOEM:
The associated early secondary air rail is shown below, which lacks the features to support a more-elaborate breather hose that BMW introduced from mid-2004 on.
While simple in design, this straight breather hose means that crankcase vapor and gasses are more likely to make their way outside the intake plenum to atmosphere while the engine is at idle and low-RPM, during which time the throttle body butterfly valves are closed and the ICV is handling all air. Emissions authorities must have frowned on this situation, because:
For production dates from mid-2004 and onwards, BMW replaced the early crankcase ventilation breather hose 11157831311 with 11157834056, the secondary air rail 13547831481 with 13417834068, the DME wiring harness 12517831646 with 12517836015, and made a DME update to support. The addition of a nipple and bracket to the secondary air rail and existence of the extra tube and valve on the updated breather hose are very apparent visual tells. The late hose incorporates an electrically operated shut-off valve under DME control that can route crankcase vapors directly into the idle-air system post-ICV, which the late air rail accepts. This CCV route allows crankcase vapor and gasses to be pulled into the engine post-ICV via the air rail while the throttle bodies are closed, which is the case at idle and at low-engine-load operation. The late hose is number 2 in the following diagram courtesy of RealOEM:
And the new-design secondary air rail features to accommodate the valve and new post-ICV recirculation route:
It turns out that as the CSL production run spanned 09/2002 - 12/2003, the CSL never received this updated hose, valve, supporting air rail, new DME wire harness, and supporting DME programming. An MSS54HP running CSL software or even an earlier MSS54 running an Alpha-N tune has no idea the new vacuum valve exists. And guess which state the vacuum valve sits in while unasserted? Open! This means the motor is free to pull air from the CCV port through the open vacuum valve and inhales it after the ICV, which represents a significant vacuum leak. While running open-loop, the DME attempts to servo the ICV, cyclically fighting the rogue excess air, and is woefully ill-equipped given the car is without a MAF when equipped with a CSL airbox, having only IAT and MAP to work with. The result is a surging, rough idle, misfires, and sometimes EML and related codes during open-loop operation shortly after both cold and warm start, before the O2 sensors have warmed enough to be useful and enable closed-loop operation to catch the excess air and compensate with more fuel. And if running Alpha-N only, sharp throttle cuts occur upon rapid throttle input increases as excess air is pulled in from the crankcase through the permanently-open valve.
My quick fix solution while I await the arrival of an early-model 13547831481 air rail is to plug the nipple in my late-model air rail and cap and tape the vacuum hose. Upon implementing this yesterday, my idle immediately became rock solid. No more surging, rough running, misfires, codes, or EML. Much smoother part-throttle operation.
TLDNR: If you have an E46 M3 with production date earlier than mid-2004 and you are installing a CSL airbox, replace your late-model 13417834068 secondary air rail with the 13547831481 early design and omit the late-design 11157834056 breather hose with its additional valve, either by replacing with a catch can setup, genuine CSL hose 11157833649, or other custom setup. You will not have a sneaky vacuum leak and will avoid idle and runtime issues.
Hope this helps someone!
I have been attempting to resolve a surging, rough, misfiring idle for awhile now that manifests only with CSL airbox installed. The issue manifests with either an MSS54 with Alpha-N tune or an MSS54HP converted to CSL spec with genuine CSL software. The issue does not manifest with the OE US airbox running a MAF and stock software on the MSS54. The issue has all the symptoms of a post-ICV vacuum leak, but I have been unable for the life of me to find the leak.
While noodling the problem the other day, the solution hit me like a ton of bricks. The culprit was indeed a post-ICV vacuum leak. An especially sneaky one.
I have a late S54 motor with a production date later than mid-2004, including all of the quality-of-life improvements BMW made.
On S54s with a production date earlier than mid-2004, the crankcase breather setup was comprised of a simple straight hose between the crankcase CCV port and the intake plenum. This hose is very similar to the hose included on the CSL. The hose is part number 2 in the following diagram courtesy of RealOEM:
The associated early secondary air rail is shown below, which lacks the features to support a more-elaborate breather hose that BMW introduced from mid-2004 on.
While simple in design, this straight breather hose means that crankcase vapor and gasses are more likely to make their way outside the intake plenum to atmosphere while the engine is at idle and low-RPM, during which time the throttle body butterfly valves are closed and the ICV is handling all air. Emissions authorities must have frowned on this situation, because:
For production dates from mid-2004 and onwards, BMW replaced the early crankcase ventilation breather hose 11157831311 with 11157834056, the secondary air rail 13547831481 with 13417834068, the DME wiring harness 12517831646 with 12517836015, and made a DME update to support. The addition of a nipple and bracket to the secondary air rail and existence of the extra tube and valve on the updated breather hose are very apparent visual tells. The late hose incorporates an electrically operated shut-off valve under DME control that can route crankcase vapors directly into the idle-air system post-ICV, which the late air rail accepts. This CCV route allows crankcase vapor and gasses to be pulled into the engine post-ICV via the air rail while the throttle bodies are closed, which is the case at idle and at low-engine-load operation. The late hose is number 2 in the following diagram courtesy of RealOEM:
And the new-design secondary air rail features to accommodate the valve and new post-ICV recirculation route:
It turns out that as the CSL production run spanned 09/2002 - 12/2003, the CSL never received this updated hose, valve, supporting air rail, new DME wire harness, and supporting DME programming. An MSS54HP running CSL software or even an earlier MSS54 running an Alpha-N tune has no idea the new vacuum valve exists. And guess which state the vacuum valve sits in while unasserted? Open! This means the motor is free to pull air from the CCV port through the open vacuum valve and inhales it after the ICV, which represents a significant vacuum leak. While running open-loop, the DME attempts to servo the ICV, cyclically fighting the rogue excess air, and is woefully ill-equipped given the car is without a MAF when equipped with a CSL airbox, having only IAT and MAP to work with. The result is a surging, rough idle, misfires, and sometimes EML and related codes during open-loop operation shortly after both cold and warm start, before the O2 sensors have warmed enough to be useful and enable closed-loop operation to catch the excess air and compensate with more fuel. And if running Alpha-N only, sharp throttle cuts occur upon rapid throttle input increases as excess air is pulled in from the crankcase through the permanently-open valve.
My quick fix solution while I await the arrival of an early-model 13547831481 air rail is to plug the nipple in my late-model air rail and cap and tape the vacuum hose. Upon implementing this yesterday, my idle immediately became rock solid. No more surging, rough running, misfires, codes, or EML. Much smoother part-throttle operation.
TLDNR: If you have an E46 M3 with production date earlier than mid-2004 and you are installing a CSL airbox, replace your late-model 13417834068 secondary air rail with the 13547831481 early design and omit the late-design 11157834056 breather hose with its additional valve, either by replacing with a catch can setup, genuine CSL hose 11157833649, or other custom setup. You will not have a sneaky vacuum leak and will avoid idle and runtime issues.
Hope this helps someone!
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