Strange problem with my e220cdi w211

[haydar]

Hi there

I have a strange problem with my e220 cdi. When I start the car, after about 2 to 3 seconds, the sound from the engine suddenly get louder (in fact embarrassingly loud). After hours of investigation the following is observed. When the alternator wires are disconnected, the engine starts up and there is no change to the sound. Once reconnected the engine noise changes after 2 to 3 seconds. I know that the alternator puts a load on the engine, but the noise is not that of the revs increasing, it's like the timing has changed and there is noticeable diesel knock. Using the STAR diagnostic tool, we observed the fuel supply at idle with the alternator disconnected is within the allowed range, but when the alternator is connected, it reads much higher than the upper limit!

The car does not consume oil, there is no smoke from the exhaust. Performance is spot on.

So my question is why would the car change its fuelling based upon if the alternator is connected or not!

The engine is very loud at idle compared to other 220cdi and it's in fact quite embarrassing.

I bought the car second hand, so is it possible that the ECU has been remapped? If so, where can I get my hands on a standard mapping for it. It is a 2002/2003 car, with the 646 engine.

 

[Uncle Benz]

I wonder if there is a voltage spike coming from your alternator which is upsetting the engine ecu. Could even be a battery fault causing an alternator spike??

Perhaps get the alternator professionally tested, or test by substitution of a known good unit.

I'm not aware of any strategy that alters the fuelling that much based on alternator load.

 

[haydar]

I thought that myself, we swapped out my alternator with a friend who has a e270cdi, but nothing changed. We also tried swapping the battery, again with no change! This is what really perplexed us?

Some how the alternator when connected causes the car to over fuel at idle, but when disconnected the fuelling is spot on as specified by the STAR diagnostic system.

 

[Uncle Benz]

Engine earth strap??

Other battery??

It's late here, and I'm just going to bed... I'll think about it!

 

[jberks]

Whats the system voltage when the alternator is connected? Is it within range?

 

[rpe2]

Don't these have a clutch on the pulley, which has a tendancy to wear out?

EDIT: Sorry, just noticed that you have swapped the unit for a KGM.

 

[television]

Don't these have a clutch on the pulley, which has a tendancy to wear out?

EDIT: Sorry, just noticed that you have swapped the unit for a KGM.

That was my thought too,,till one reads on.

An oscilloscope will tell all

 

[haydar]

Not all w211 came with the clutch pulley. In fact the friends alternator was a clutch pulley type.

We checked all the earth straps today, including the battery and even gearbox ones. All were fine. Again, when the car is started it sounds perfect for about 2-4 seconds, before the sound changes. Injectors are new, air mass sensor is new (plus it has been swapped in the past from my friends car, which we know works fine.)

Malcolm, please explain the oscilloscope test. Not sure if we have one but I'm sure we could find it.

If the car has been remapped, how can one take it back to standard?

Thanks

 

[television]

With a scope you can see the condition of the output from the alternator and see if any nasties are present .

The coding can be read on STAR for any mapping that may have been done, it really is an odd fault.

You could run the engine without the alternator connected and see

 

[Aviator]

Monitor the battery voltage when you start the car this should increase,if the battery voltage decreases when the engine noise changes this would indicate a load on the alternator.

 

[haydar]

OK, will monitor the battery voltage tomorrow. If we disconnect the alternator, then the sound of the engine does not change at all.