E320 M104 power loss
 

Hi
I need some guidance.
My E320 W104 1995, runs fine, except for a decrease in torque from about 3000 rpm. Currently the torque increases from about 4000 rpm, and at lower revs it is pretty flat compared to what it use to be.

Can it be the resonant flap in the inlet manifold ?
How is this flap actuated, electrically or electro-pneumatically. I do not see a vacuum line to the actuator.
Can it be cleaned or serviced?
At what speed does the flap change position?

Can it be the cam advance?
The solenoid is alive as can 'audibly' move the piston when externally actuated from the battery.
The signal to the solenoid is high between about 3000 and 4000 rpm

Can the MAF sensor function partially and cause this problem while the engine runs normally in other regions.
Fuel consumption increased from 10l/100km to just under 11l/100 km since the problem started.

Wiring harness is new.

I could not locate any meaningful fault codes from pin 8 in the 16 pin connector. It gave 36 flashes and 42 flashes. These are unknown to me. I have reset the codes and will check after running a few days.

Any ideas would be appreciated !
Thank You
Gerritt Visser

36 is purge system.
It may be stuck/gummed up..
The cam change is at 3k and the flap is at 4k. [3900]
*Note-these rpms are No Load/P-N gear select. Under driving load conditions, they vary according to load/ecu mapping.
Cam check advance can be checked with your power jumper at idle ..look for rough idle w/power.
Purge can be felt in you hand as a heartbeat . Check the vac hoses and on/off of vac flow with the oscillations [ about 5/9 beats p/sec]....
Post codes from EA [ 14]............

Thanks for the reply Arthur.

I've checked the purge solenoid valve. It is clean, seals well and opens when powered. I can blow freely through the vacuum tubes.
The valve 'beats ' as you described.

The idling speed drops rapidly when the cam adjuster is activated.

Code from pin 14 is 1 flash.

From what you said the torque increase at ~4000 rpm is due to the resonant intake manifold. It seems as the power loss in the 3000 to 4000 rpm range coincides with the cam advance. I'll try to determine if the solenoid is activated while driving.

What is the short tube on the actuator of the resonant flap, next to the connector? Is it an adjusting screw, and if so, how is it adjusted? This seems to be a very unknown part of the engine as it does not appear in any manuals. Not even in the factory CD's that I have. Perhaps it never causes any trouble.

The resonance flap acuator is the switch-over-valve. I am not sure if it is adjustable [ that may be the factory calibration screw]
Under full load , the ecu actually calls for an activation rpm of SOV at 3350...
The adjustment should not have anything to do with rpm activation, [ as that is ECU electrical SOV sig]. but it may effect vac flow variable...

Checked my cam advance switching points.
It does not seem to very losd related as it happens at the same rpm under gantle driving and hard acceleration.
Advance activated at ~1750 rpm.
De-activated at ~ 1250 rpm.
Remains activated up to >5000rpm.
Curent ~1.0 amp during activation.
It seems as if this is OK as it agrees with the values in MB doc 05-2160.