E220 CDI rough idle, and charging voltage

[starfinder]

Hi Guys, :bannana:

Need some advice before bringing my car to the local MB dealer for diagnostics.

Car: E220 CDI MY 2001, Automatic

For the past month or so I have noticed that the engine frequently runs a little rough at idle, not much but still perceivable. When this happens the charging voltage start to fluctuate between 12-13V (read out on the climatic control display by pressing the ‘rest’ button and selecting menu 24).

I have not yet got a charging warning, but as a electronics engineer it seems strange that the voltage fluctuate so much. When the engine runs smooth at idle the voltage is stable at 13.3V.

Have anyone experienced something like this or just any good ideas! – Is it likely that a worn generator or defect regulator can cause this idle problem or is it more likely something to do with the defect injector/ high pressure pump drawing too much current, i.e. forcing the voltage to fluctuate? The car starts without any problems!

I have also noticed another strange thing! - When engine is cold (just started) and I stop at a red light (engine still very cold), the whole car seems to shake forth and back at idle. When pulling away at green light, the car seems to run for a longer time in 1.gear than usually before shifting up. - Is this due to some emission related thing for CDI cars, and normal?
Not a problem when engine is hot or has been running from cold for more than 5min.

BR

Starfinder

 

[Brian WH]

Hi Guys, :bannana:

Need some advice before bringing my car to the local MB dealer for diagnostics.

Car: E220 CDI MY 2001, Automatic

For the past month or so I have noticed that the engine frequently runs a little rough at idle, not much but still perceivable. When this happens the charging voltage start to fluctuate between 12-13V (read out on the climatic control display by pressing the ‘rest’ button and selecting menu 24).

I have not yet got a charging warning, but as a electronics engineer it seems strange that the voltage fluctuate so much. When the engine runs smooth at idle the voltage is stable at 13.3V.

Have anyone experienced something like this or just any good ideas! – Is it likely that a worn generator or defect regulator can cause this idle problem or is it more likely something to do with the defect injector/ high pressure pump drawing too much current, i.e. forcing the voltage to fluctuate? The car starts without any problems!

I have also noticed another strange thing! - When engine is cold (just started) and I stop at a red light (engine still very cold), the whole car seems to shake forth and back at idle. When pulling away at green light, the car seems to run for a longer time in 1.gear than usually before shifting up. - Is this due to some emission related thing for CDI cars, and normal?
Not a problem when engine is hot or has been running from cold for more than 5min.

BR

Starfinder

All this is controlled by the Engine Management System the ECU and there appears to be a problem with fuel delivery when cold. I would get your dealer to put it on the Computer and see what is wrong.

 

[silverarrow]

check the valve seats on the injectors loads are leaking only pence per copper washer and 2 hrs to fit

 

[starfinder]

Thanks guys! - I will have this in mind when I go to my local MB dealer tomorrow for diagnostics.

BR
Starfinder

 

[PJH]

When pulling away at green light, the car seems to run for a longer time in 1.gear than usually before shifting up. - Is this due to some emission related thing for CDI cars, and normal?
Not a problem when engine is hot or has been running from cold for more than 5min.

BR

Starfinder

The delayed up change from 1/2 & 2/3 is common to the petrol engined cars as well. I think it helps the catalyst warm up quicker.

 

[Cclass guy]

The delayed up change from 1/2 & 2/3 is common to the petrol engined cars as well. I think it helps the catalyst warm up quicker.

I'm having a bit of rough idle myself, but don't want to start a new thread. The rough idle only happens when the car temperature exceeds 80 degrees. I changed the spark plugs some 2k kilometers ago. Might be better if I cleaned them right? What's the correct procedure?

Thanks.

 

[starfinder]

Hi Guys,

Finally solved the problem with rough idle on my MY 2001 E220CDI. The cause was a defective electronic heat booster unit.

It seems that some CDI models are fitted with an electronic heat booster (1.5KW) that helps heat-up the cooling water when the outside temperature is below +8ºC and the water temperature is below +80ºC. This unit is controlled by the generator and the outside temperature, and should only load the system if excess capacity on generator is detected.

After changing this unit it is back to normal again.

Best regards,

Starfinder

 

[Madferrit]

can you give a rough cost of what you had to spend to get it sorted? just in case i encounter something similar

 

[williaj6]

Glad all is now OK. How did you discover that it was the electronic heat booster unit? I assume it was diagnosed by the computer at MB? I have a problem with symptoms similar to those that you were experiencing on my 320CDI (2000). It's been on the Bosch computer but no errors were reported. Fuel readings across all injectors at idle and at higher revs looked OK.

 

[starfinder]

Glad all is now OK. How did you discover that it was the electronic heat booster unit? I assume it was diagnosed by the computer at MB? I have a problem with symptoms similar to those that you were experiencing on my 320CDI (2000). It's been on the Bosch computer but no errors were reported. Fuel readings across all injectors at idle and at higher revs looked OK.

Hi williaj6,

Like you I took my car to the local MB dealer, and they put it on the tester - everything looked fine! They checked the whole injection system twice and could not find anything wrong. They came up with various ideas on what could be the cause to what I was experiencing, but it all sounded a little too far out (something like I needed to have the torque converter in the transmission changed at a cost of £1000) - So I left again!

The next few days I paid special attention to when the rough idle actually occurred. I found out that it was most dominant when cold outside and the water temperature had not yet reached its operating temperature. When the water temperature reached operating temperature the rough idle just vanished.

Since MB could not replicate the symptom when I first had them look at it I started to think – which conditions did they actually test it under. I came up with the idea that the difference was the outside temperature. They tested it in a nice warm garage, of cause they do!

I then took my car to a nice warm parking space at the local shopping center and tried my theory, and sure enough no problem! The next day I phoned MB and asked them if anything that could load the engine was activated/ deactivated as a result of the outside temperature. - The answer was the electronic heat booster! I then disconnected the control signals for this unit and everything was fine.

I then talked to my local MB dealer again, and it seems that this part is very unreliable. It can even make you car go up in flames.

The unit costs about £180 + workshop cost £50, but since MB could not find the problem themselves they agreed to pay half. :bannana:


Best regards,

Starfinder

 

[williaj6]

Starfinder--

Thanks for all the help.. My car went to MB and their computer suggested the problem was a faulty injector. They replaced it (£340 inc installation) and my problem has gone away. The computer should an injector readin of 5.1 on idle with the tolerance allowed up to 5.0 above which MB suggest haging the injector (didn't sound too convincing to me that this was the problem - but it worked).

By the way we checked for the booster heater that you suggested and apparently my engine doesn't have one (year 2000 X reg 320 CDI).

Many thanks again for the info.