03-12-2012, 03:02 PM
Intake Resonance System Overhaul for the 1991-1993 E34 //M5
1Intake Resonance System.ppt (Size: 3.59 MB / Downloads: 24)
System Background
The intake resonance system is used to increase the torque at full throttle when engine speed is less than 4120rpm and greater than 6720rpm. At 3500rpm the average torque is increased by approx 15%
The system is not energized (valve left open) if engine speed is not within this range AND full throttle is not applied.
During engine startup the resonance flap can be observed performing its self test (evident by looking at the linkage at the top of the intake plenum). My 1991 M5 (145000 miles) did this intermittently and then finally ceased this self-test. My 1993 M5 (41000 miles) does this self-test at EVERY engine start.
As the system ceases to function, a substantial drop in torque is felt in the 2500-4000rpm range. This is often accompanied by a “switch-like” response as the engine torque increases rapidly In the 3500-4000rpm range. Here is a comparison of engine torque for a properly working resonance flap and a non-operational one. The following curve was extracted from the BMW Technical Reference Information on the S38-B36 Engine. A copy can be found at http://bmwe34m5faqs/
Tools Required
The 10mm socket is used to remove the top 2 nuts holding the throttle cables
The 10mm ratcheting box end wrench greatly facilitates the removal of the acorn nuts holding the throttle bodies to the rest of the engine and the air filter
The 6 and 7mm sockets are used to remove various hose clamps (sizes may vary so check to insure appropriate socket is used)
The 13mm wrench is used to remove the two nuts holding the bottom of the intake manifold to the engine
Resonance System Vacuum Line Removal
The changeover valve is attached via clips that hold both ends of the valve to the engine. Just gently pry open the clips and lift away the valve.
The vacuum reservoir is held by a rubber flexible “clip” that attaches to a bracket assembly.
Once one familiarizes themselves with the routing of the lines, removal is trivial. Just make sure that all the lines get hooked up to their original locations! Take care in noting the location and termination of the lines.
I replaced all the vacuum lines that I could get my hands on, which is pretty much all of them, with new OEM rubber. Also, it might be a good idea to replace all hose clamps that you can get to. At 145000 miles my clamps and vacuum lines were showing significant signs of embrittlement as well as poor hose clamp condition. While you have the plenum off, you might as well replace any hoses that you can get to, which happens to be quite a few!
The next page shows a part of the resonance vacuum system. Page 21 is an excellent diagram that I found on the internet showing the layout of all vacuum lines and where they originate and terminate.