Vlad
MB Enthusiast
Nice to hear you have the straight 6.....lovely engine....in my opinion!....and yes, they real let fly at 4000 rpm.
These engines/electrics do have a couple of maintenance issues that rarely get looked at in a service.
1) Stumbling/surging revs. Typically shows up whilst you are stationary at the lights waiting for them to change. The car can start surging against the brakes and the rev needle will start hunting up and down.
This is normally caused by a dirty butterfly flap in the throttle body which causes a small air leak and confuses the ECU.
Its easy to clean....here goes....take off the trunking that snakes over the top of the engine from the air-cleaner. Also disconnect it from the mouth of the throttle body as it plunges over the edge of the engine on the right hand side.
Now you will be able to see into the throttle body. Inside you will see a round disk about 5cm down into the throttle body.....this is the butterfly flap. Spray some carb cleaner down into the throttle body. Get a screwdriver with some rag tied tightly around it and then push down on the edge of the butterfly flap. As it flips up you will probably notice that the edge o the flap has a build up of black crud on it. Cean this off with the rag and do it on the other side of the flap by pushing down on the opposite side.....this black crud stop the flap from sealing correctly.
Once done put everything back together again.
Now look at the trunking on the top of the engine, at the top right hand bend there is a sensor which is a push fit. Release this and you will notice that there is a fine wire element at the end of the sensor. Its likely to have a film of oil on it. Spray some carb cleaner and gently wipe it off with a lint free cloth.....re-fit.
2) If your car still has a stumbling idle move to step 2.
These cars are fitted with an Over Voltage Protection relay...OVP. The original relays that were fitted to the M104 engines had a design flaw in them which causes the internal soldering to start breaking down. This will typically manefest itself by the car stalling for no reason whilst coming to a halt and then being hard to start or you may just find the car hard to start full stop. If your car is still on the original OVP get it changed as it will fail....guaranteed!.....costs about £60 and takes 10 minutes or less to change depending on the car you have.
3) Still got a stumbling rev....step 3. Normally on the right hand inner wing you have a small unit called (I think) the EGR valve that has a couple of vacuum tubes coming out either side of it...this item has MOT stamped on the top of it. This valve can get a build up of carbon in it which will cause the engine to idle badly. Costs about £50 and is very easy to replace as it is just pushed onto a metal peg.
4) Water leak. On my E280 I had a continued water leak...all hoses, radiator etc were fine. Turned out that there was a leak right at the back of the engine on the right hand side....you can't see it as its behind the inlet manifolds. Turns out that there is a hose that goes into the back of the engine that has a small O ring sealing it...this can fail and cause the cooling system to loose water. The mechanic I use, had a look staright away at this location with a torch and noticed that the rear of the block was damp with coolant.
He replaced the O ring and said it was quite common for these to fail. I have no idea how he managed to get to it....looked well tricky to get at. But he did it and the price for replacement was reasonable and after that the car never lost any coolant.
Hope this helps
These engines/electrics do have a couple of maintenance issues that rarely get looked at in a service.
1) Stumbling/surging revs. Typically shows up whilst you are stationary at the lights waiting for them to change. The car can start surging against the brakes and the rev needle will start hunting up and down.
This is normally caused by a dirty butterfly flap in the throttle body which causes a small air leak and confuses the ECU.
Its easy to clean....here goes....take off the trunking that snakes over the top of the engine from the air-cleaner. Also disconnect it from the mouth of the throttle body as it plunges over the edge of the engine on the right hand side.
Now you will be able to see into the throttle body. Inside you will see a round disk about 5cm down into the throttle body.....this is the butterfly flap. Spray some carb cleaner down into the throttle body. Get a screwdriver with some rag tied tightly around it and then push down on the edge of the butterfly flap. As it flips up you will probably notice that the edge o the flap has a build up of black crud on it. Cean this off with the rag and do it on the other side of the flap by pushing down on the opposite side.....this black crud stop the flap from sealing correctly.
Once done put everything back together again.
Now look at the trunking on the top of the engine, at the top right hand bend there is a sensor which is a push fit. Release this and you will notice that there is a fine wire element at the end of the sensor. Its likely to have a film of oil on it. Spray some carb cleaner and gently wipe it off with a lint free cloth.....re-fit.
2) If your car still has a stumbling idle move to step 2.
These cars are fitted with an Over Voltage Protection relay...OVP. The original relays that were fitted to the M104 engines had a design flaw in them which causes the internal soldering to start breaking down. This will typically manefest itself by the car stalling for no reason whilst coming to a halt and then being hard to start or you may just find the car hard to start full stop. If your car is still on the original OVP get it changed as it will fail....guaranteed!.....costs about £60 and takes 10 minutes or less to change depending on the car you have.
3) Still got a stumbling rev....step 3. Normally on the right hand inner wing you have a small unit called (I think) the EGR valve that has a couple of vacuum tubes coming out either side of it...this item has MOT stamped on the top of it. This valve can get a build up of carbon in it which will cause the engine to idle badly. Costs about £50 and is very easy to replace as it is just pushed onto a metal peg.
4) Water leak. On my E280 I had a continued water leak...all hoses, radiator etc were fine. Turned out that there was a leak right at the back of the engine on the right hand side....you can't see it as its behind the inlet manifolds. Turns out that there is a hose that goes into the back of the engine that has a small O ring sealing it...this can fail and cause the cooling system to loose water. The mechanic I use, had a look staright away at this location with a torch and noticed that the rear of the block was damp with coolant.
He replaced the O ring and said it was quite common for these to fail. I have no idea how he managed to get to it....looked well tricky to get at. But he did it and the price for replacement was reasonable and after that the car never lost any coolant.
Hope this helps
