Technical Alternator only generates after revving

[nigelvan]

My X250 3.0 from 2007 has this problem for over a year now, it seems not critical but I think I need to address this anyway:
When performing a cold start the alternator does not generate electricity. I can tell by the battery voltage staying at around 12-13V.
The battery light (E050) doesn't come on but the ECU starts revving the engine a bit higher to about 1100RPM. This is however not sufficient and I have to manually rev the engine to about 1200rpm, then the alternator suddenly kicks in and voltage jumps to 14V. Everything after that is fine, battery charges, no voltage fluctuations. With a warm engine this issue is less likely to occur.

I checked the D+ connection that is supposed to send some initial exciter current and I measure 0.7V until the alternator kicks in.
I had a bad earth connection before so I double checked the straps and the engine block has multiple additional connections to the chassis. Also, the accessory belt was replaced recently by myself.

Also interesting: if I rev too agressively the engine will stall and throw a code about the fuel pressure solenoid, I suspect because the battery can't supply the sudden change in current? Of course when the alternator is in operation this doesn't happen and the vehicle drives fine otherwise.
I could try and replace the entire alternator of course, but that job is quite involved and I would need to remove the axle etc...

 

[Communicator]

Hi Nigel,

I think that the following points have been raised in your previous thread relating to your alternator.

1. Please confirm that alternator is an OEM part, and has not previously been replaced. If non OEM alternator has been fitted, it may not interface correctly with the BCM.
2. How many miles/kilometres has the vehicle covered? The brushes have a finite life.
3. As the veicle is a campervan, are other circuits attached to the D+ point? These could pull the D+ point down. Try removing split charge relay, AES fridge connections, etc.
4. Could the engine stalling be due to over revving? The ECU can reduce fuel input if engine is over revved.

 

[nigelvan]

Hi Nigel,

I think that the following points have been raised in your previous thread relating to your alternator.

1. Please confirm that alternator is an OEM part, and has not previously been replaced. If non OEM alternator has been fitted, it may not interface correctly with the BCM.
2. How many miles/kilometres has the vehicle covered? The brushes have a finite life.
3. As the veicle is a campervan, are other circuits attached to the D+ point? These could pull the D+ point down. Try removing split charge relay, AES fridge connections, etc.
4. Could the engine stalling be due to over revving? The ECU can reduce fuel input if engine is over revved.

Hi Communicator,
Thanks for coming back to me. I'm sorry, I totally forgot I posted earlier about it and it's bad forum etiquette. I just reread it.

1. It is an OEM part, I never had problems before the last 10k km or so
2. Now it's at 165k km, bought it at 114k, that doesnt seem excessive
3. No, I never used the D+ connection on my DC-DC, it's in voltage sensing mode. So the D+ circuit is completely left untouched
4. I don't rev it that high, up to 2000rpm at most because I know it just needs a little 'nudge' so to speak. But I'm not worried too much about that... although it might maybe point to some sort of loss on the + part between battery and engine (starter/alternator)

 

[Communicator]

Hi Communicator,
Thanks for coming back to me. I'm sorry, I totally forgot I posted earlier about it and it's bad forum etiquette. I just reread it.

1. It is an OEM part, I never had problems before the last 10k km or so
2. Now it's at 165k km, bought it at 114k, that doesnt seem excessive
3. No, I never used the D+ connection on my DC-DC, it's in voltage sensing mode. So the D+ circuit is completely left untouched
4. I don't rev it that high, up to 2000rpm at most because I know it just needs a little 'nudge' so to speak. But I'm not worried too much about that... although it might maybe point to some sort of loss on the + part between battery and engine (starter/alternator)

1. So something that has developed during ownership.
2. I have had alternator brushes wear out with less distance resorded. Thinking about that, if brush contact resistance is too high alternator may fail to start generating.............
3. So no power extracted from D+.
4. See diagram attached in previous thread. On x250 power output from alternator is to starter terminal, then via jump start point to CAL4 fuse at battery positive. Distribution is from battery positive.

Follow advised procedure to disconnect battery negative, before working on battery positive connections.

 

[nigelvan]

Following your point 2, if the brushes are indeed wearing out, it would explain why the orginal exciter voltage is not enough to 'start' the alternator. It's a bit strange though why the BCM doesn't trigger the E050 light on the dash. I wonder what the right D+ voltage is, I'll dig a bit deeper in eLearn (which is on the Stelantis site now)

4. I'll check this as I feel the starter motor doesn't get all the juice always for a smooth start, except with a full battery. Maybe some corrosion there after all the years.

 

[Communicator]

Following your point 2, if the brushes are indeed wearing out, it would explain why the orginal exciter voltage is not enough to 'start' the alternator. It's a bit strange though why the BCM doesn't trigger the E050 light on the dash. I wonder what the right D+ voltage is, I'll dig a bit deeper in eLearn (which is on the Stelantis site now)

4. I'll check this as I feel the starter motor doesn't get all the juice always for a smooth start, except with a full battery. Maybe some corrosion there after all the years.

4, Starter motor main current path is from battery +ve to starter solenoid via jump start point. Return includes engine block earth strap, of which you are aware, and battery -ve earth connection.
I have seen a report of a partially fractured battery +ve clamp. It could have been either M6 clamping bolt, or pressed metal clamp.

 

[nigelvan]

@Communicator I found this thread with you involved where the OP stated that he measures about 10V on D+ with the ignition on (engine not started), while I only measure 0.7V. Now I do have an electronics background and 0.7V seems like a very low voltage to send over such a distance to the alternator. Also since this signal comes straight from the BCM this seems like a very weird voltage to generate with the use of a microcontroller. But it is a diode voltage...
Because of the bad weather here I did some more googling online to this issue brand-independent (found some old Benz thread with similar issue) and it seems my alternator is basically self-exciting by revving the engine a bit, or at least that sounds like a very plausible explanation.
I did measure D+ at various point like M001 (you can easily slide out the 2 subconnectors from the main connector in order to shove a needle in to the multimeter) and D004. Could a connection problem between M001 and the BCM (somewhere behind it I suppose) be the cause?
I could of course feed 12V directly via D004 to D+ to see if the alternator starts up this way...IF I'm sure this is what the D+ can handle. However, I can't find anything in ELearn on D+ voltage pre-ignition.

EDIT: I found in the other thread the expected voltage on D+ (around 1V while cranking) so 0.7V seems in the right ballpark.

 

[nigelvan]

With the weather clearing up I went ahead and cleaned all high current positive wire junctions, at the junction box and the starter motor. Some minor corrosion but no red flags. I also found some corrosion in the D004 connector when I finally got it to come apart. Unfortanetly not causing the issue.
In the older thread I found D+ should be around 1V before the alternator is generating, so I refrained from putting 12V on it. 0.7V seems close enough.
So next thing I'll check is the connector to the alternator.
@Communicator you might be right about the brushes but I'd like to rule out anything else. My personal experience tells me the quality of parts hasn't gone up in general so I like to be sure before throwing a new alternator at it.

 

[Communicator]

With the weather clearing up I went ahead and cleaned all high current positive wire junctions, at the junction box and the starter motor. Some minor corrosion but no red flags. I also found some corrosion in the D004 connector when I finally got it to come apart. Unfortanetly not causing the issue.
In the older thread I found D+ should be around 1V before the alternator is generating, so I refrained from putting 12V on it. 0.7V seems close enough.
So next thing I'll check is the connector to the alternator.
@Communicator you might be right about the brushes but I'd like to rule out anything else. My personal experience tells me the quality of parts hasn't gone up in general so I like to be sure before throwing a new alternator at it.

Exactly, I also do not like spending on unnecessary items. I wonder if it is possible to obtain new brushes? If eventually needing to remove the alternator, see last lines of post #13 in you previous thread.