Intake Resonance System Overhaul for the 1991-1993

E34 ///M5

Jason Weaver June 1 ,2003

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://bmwe34m5.com/faqs/

Torque is much more linear in this region

Tools Required Phillips Head Screwdriver

Ratchets with 10mm, 7mm and 6mm sockets

Ratcheting box end 10mm wrench

10mm and 13mm Wrenches

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

Intake Plenum Removal Instructions

1)  Loosen 2 10mm nuts holding airbox

2)  Remove Connectors to MAF (one on the top and one located underneath top connector)

3)  Remove Intake Boot from both plenum and MAF

4)  Pull out airbox carefully (Airbox and MAF come out as single unit)

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1

2

3

1)  Remove throttle cable by pinching plastic ends and sliding cables out

2)  Remove 2 nuts holding throttle cable assy and place cables out of the way

3)  Remove 12 acorn nuts (10mm)

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2

3

Remove vacuum line from top of plenum (connecting to valve actuator) by pulling out. Careful, its easy to tear the rubber line as well as crack the plastic “L”

Valve Actuator

Remove hose directly underneath Plenum intake chamber

Air flowing from MAF to Intake Plenum

1)  Remove hose from bottom tip of plenum

2)  Remove 2 13mm nuts. These attach the plenum to the engine bracket assy.

1

2 (Can’t see nuts but they are under there. Just feel around with your finger tips

Remove connector to electric valve

1)  Once all screws and hoses removed carefully pull plenum away from throttle bodies. Notice the hose that needs to be disconnected as well as some vacuum lines?

2)  Disconnect hose clamp and remove hose

3)  Remove 2 vacuum lines from plenum

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3 (See next page for close up)

PLENUM

Remove these 2 hoses carefully. Plenum can now be removed from engine bay. Note plastic coil protective sleeve around vacuum hose

Place plenum on soft towel to prevent damage. Actuator: Should

actuate during every engine start

Intake gaskets on each horn

May be a good idea to inspect and replace intake gaskets at this time.

To actuator on top of plenum

To Bottom “T” branch Vacuum line

Electric Valve

A

B

After removal of the plenum one can see the mass of hoses and vacuum lines that feed the M5.

Vacuum Reservoir

Changeover valve located behind these lines

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.

Attaches to throttle bodies

Changeover valve (note orientation)

Vacuum Tank Reservoir To Air pump electric valve…see page 19

To Intake Plenum “B” (electric valve mounted on plenum…see page 16)

Air Pump electric valve…Vacuum line connects here

Idle Control Valve