Hi Davor, and welcome to the forum! Thank your for filling out your user profile so we know exactly what car you have and where you are located - that is very helpful!

The regulator is designed to output 14.0v, but it will fluctuate. Operating electrical consumers will place a greater demand on the alternator, as will accelerating (the coil packs need power, too). So, fluctuations between 13.2v and 14.1v ar normal. If you see it going very low, below 13.2v or you experience some electrical "gremlins", you may have a bad regulator or even a bad alternator.

 

Thanks for the initial comments Rudeney. I have a feeling that the issues I am having with the car are very delicate and connected to the system voltage. I think that very advanced members of this forum will find this thread interesting as I plan to go into detail to solve these issues that may be of interest to many other members with related unsolved issues.

I am aware that WIS suggests that any voltage between 13.5 and 14.5V is “OK”. However, my evidence suggests otherwise. As mentioned before, there are gremlins showing up when the voltage is on the low side. I have observed the following major issues with low voltage:

- transmission is shifting poorly; when transmission reaches operating temp and voltage is 14.2 or more, it shifts like a dream, further the voltage goes below 14.2, more rough the shifting becomes;
- engine pinging; lower the voltage, more pinging occurs; putting 98 RON doesn’t help much that I have noticed, it doesn’t appear to be fuel quality related.

In addition to these and many other glitches, for example, when the car is idling (perfectly) and I close either of the doors, and windows move to seal off, the voltage goes low momentarily to such extent that the idle drops momentarily and obviously. I just can’t imagine that this is normal. I will need to make an audio or video clip to show this.

As it is getting late here in the land down under, I will continue to present my discoveries tomorrow. I haven’t even gotten to the part about apparent temperature dependence and things I actually suspect with the alternator. At this stage I am quite sure the alternator is not behaving normally and I have some theories about it. Hence, another voltage regulator is on its way as well as slip rings.

Good night.

 

Thanks for the initial comments Rudeney. I have a feeling that the issues I am having with the car are very delicate and connected to the system voltage. I think that very advanced members of this forum will find this thread interesting as I plan to go into detail to solve these issues that may be of interest to many other members with related unsolved issues.

I am aware that WIS suggests that any voltage between 13.5 and 14.5V is “OK”. However, my evidence suggests otherwise. As mentioned before, there are gremlins showing up when the voltage is on the low side. I have observed the following major issues with low voltage:

• transmission is shifting poorly; when transmission reaches operating temp and voltage is 14.2 or more, it shifts like a dream, further the voltage goes below 14.2, more rough the shifting becomes;
• engine pinging; lower the voltage, more pinging occurs; putting 98 RON doesn’t help much that I have noticed, it doesn’t appear to be fuel quality related.

In addition to these and many other glitches, for example, when the car is idling (perfectly) and I close either of the doors, and windows move to seal off, the voltage goes low momentarily to such extent that the idle drops momentarily and obviously. I just can’t imagine that this is normal. I will need to make an audio or video clip to show this.

As it is getting late here in the land down under, I will continue to present my discoveries tomorrow. I haven’t even gotten to the part about apparent temperature dependence and things I actually suspect with the alternator. At this stage I am quite sure the alternator is not behaving normally and I have some theories about it. Hence, another voltage regulator is on its way as well as slip rings.

Good night.

Hello, did you manage to fix your problem ? im having the exact same problem ! My car is a 2002 CLK 240 with M112 engine and 722.6 AT
i did some testing and found out that instrument cluster dim and interior lighting as well while operating power windows or putting high beam on . while doing this the voltage drops from 14.3 to 12.7 for a second or two and then shoots back at 14.3 . this symptoms does not occur frequently but when they occur i also notice that the transmission shifts are harsh . i

 

I'd use an analog dial type to see if the voltage is actually spiking lower - digital voltmeters are dampened and can smooth out quick spikes. If a new (quality) regulator does not help, I'd suspect the alternator itself may be the problem and it just can't keep up with the demands of the electrical consumers. Another possibility is the battery. If it has collapsed plates, they can act like resistance in the electrical system and keep the alternator form supplying proper current. Also check your wiring at the battery, alternator, and ground points for any corrosion or poor connections.

 

All valid points. I have actually even used oscilloscope to follow the alternator voltage, so I have the most accurate and responsive signal in that regard.

Battery is only 1.5 years old, good quality Exide. 12.6V holding no engine running, seems very healthy and fast cranking. Haven’t yet measured cranking voltage. Current draw by the battery + system via alternator cable is around 2.6 Amps (lights off, heater fan off, all accessories off) seems pretty steady and independant of conditions.

Haven’t checked battery cables + terminals yet, but I figure if the voltage at the battery terminal (post) is more or less equal to voltage at alternator B+ then I shouldn’t have any cable/terminal/corrosion issues as such. There is 80mV drop from alternator B+ to battery +ve, but that should be normal.

I am still suspecting alternator, namely VR and/or sliprings (which are in pretty bad condition after 175000 miles. I have taken some graphs of the voltage as measured by the obd2 scanner. I will post them tomorrow together with my findings and theories.

As always, any comments and/or suggestions appreciated.

 

I am now almost certain that "bad" voltage is the root cause of many problems with my car, and any other car for that matter, that is experiencing similar symptoms.

Hooked up fuel pressure gauge. Idling with 56 psi, totally expected and normal. Now, if I repeat the test described in the first post of this thread, where I close a door and window moves up to seal off (or do any other action that has the same effect), the voltage drops and the idle speed dips (already stated that before). The information that is now new, is that the fuel pressure ALSO dips by few psi at the same time and it causes momentary drop in idle speed. Closing a window or a door causes voltage to sometimes drop below 13V, but only momentarily, for a second or so, but which is sufficient to make the idle also momentarily drop. I suspect that this instant voltage drop also has an effect on fuel injectors and ignition, and with all three combined (lower fuel pressure, injector opening slower and perhaps weaker ignition at that point) there is enough combined effect to clearly influence fuel delivery at that moment and cause momentary idle drop.

At this point, anything is possible but my number one suspect is still low voltage and inefficient alternator as a whole, whether it be VR or anything else within the alternator. Cannot wait to receive the new VR and slip rings.

Anyone has something to add, perhaps some things to test?

P.S. A brand new fuel pump was installed 10 months ago (first one completely failed withing 500km of the first symptoms). Therefore, I tend not to blame the fuel pump. However, this drop in fuel pressure could explain the engine ping under heavy load that SOMETIMES happen, not always. I was blaming MAF, but that may not be the case. Anyway new Bosch (hopefully genuine this time) unit is on its way.

 

53psi is the low end of proper fuel pressure (the range is 3.7 - 4.2 bar, or 53.66psi - 60.91psi). Another test of the fuel pump is for current draw. It should pull between 4 and 9 amps. Of course at idle, it should be on the low end of both test's ranges.

Another factor in the idle speed dropping as voltage drops is with ignition. The coil packs do require a good bit of power to operate, so if they are getting "choked" off yo might not get full spark, or the second plug may not be firing. You should never see voltage drop below 13v when the engine is running. I'd say anything below about 13.5v would be cause for concern.

One way to test to see if it's the battery is to start the engine, then carefully disconnect the negative lead from the battery. If the alternator is good, the car will run just fine. If not, then you have an alternator/regulator problem. If the car runs fine with the battery disconnected, but then has problems with the battery in the circuit, then I'd suspect a bad battery (yes, I know it's relatively new, but it could still be defective). Reconnect the battery before shutting off the engine. Of course be careful handling the battery lead - use smooth, certain motions to disconnect and reconnect it. You'll get a tiny spark, but you don't to "stutter" the connection and create fireworks.

 

Thanks for the comments Rodney. I will do some testing tomorrow, as it is already 10.30pm here. I will give an update. The plan is to measure voltage AND current for the fuel pump, near the fuel pump (but not at the pump connector itself). This will tell me if there is excessive voltage drop from the battery to the fuel pump. I am hoping that the voltage at rear SAM and the fuel pump relay (while the car is running and circuit is loaded) will closely follow battery terminal voltage, under all operating conditions. The full path of supply seams to be (according to WIS schematics, attached):

Battery +ve terminal => prefuse box link no.2 (200A) => rear SAM => fuse 4 (fuel pump) => relay kA contact (fuel pump relay) => X36/3 (fuel pump connector).

Will also do running test with battery disconnected.

I will get to the bottom of these issues, otherwise I will quit engineering career. :wink

 

Live voltage plot (as captured by OBD scanner) while operating windows (trying to close already closed windows causes the window mechanism to engage for a second while drawing large current and dropping the system voltage). This voltage drop can also be achieved in many different ways. And as mentioned, when the voltage drops by this large amount, the idle momentarily suffers.

The clicking sound is the windows trying to move. Also, due to slower update speed of the OBD2 scanner, the voltage drop is not always captured. I will have to use oscilloscope for most accurate measurements.

 

Live voltage plot (as captured by OBD scanner) while operating windows (trying to close already closed windows causes the window mechanism to engage for a second while drawing large current and dropping the system voltage). This voltage drop can also be achieved in many different ways. And as mentioned, when the voltage drops by this large amount, the idle momentarily suffers.

The clicking sound is the windows trying to move. Also, due to slower update speed of the OBD2 scanner, the voltage drop is not always captured. I will have to use oscilloscope for most accurate measurements.

https://www.youtube.com/watch?v=_t4S8DZeufs

It is more like a grounding problem. Connect your scope between the battery terminals and repeat the test. Resistivity between the ground terminals can raise the ground level, which affects more circuits than a resistive battery+ path.

 

I think you have a voltage supply problem. Did you try disconnecting the battery?

 

I concur with rudeney, I feel like you have a battery issue. I would run a load test on the battery. A place that sells batteries will do that for you for free. With a good battery you would not have much of a spike when demand is put on it. It is really not up to an alternator to supply power to your appliances. The alternators job is to charge the battery.

 

Battery + engine running draw only 2.6 Amps, as measured with DC clamp at the alternator cable

This does not sound right to me. The alternator output should be much higher. Just the fuel pump alone should be drawing 4 amps. If the alternator is only putting out 2.6 of that, then it's drawing off the battery. While gorj and I may disagree about the function of the alternator, I can tell you that if the alternator is not outputting more amperage and the vehicle is demanding, then it is running off the battery and that is a problem.

 

Test results

Hello everyone involved in this thread. I have done some extensive tests and have interesting results.

Rodney: I have done the test where battery is disconnected while engine is running off alternator alone. See the results below.

With full load, low+high beams on, blower to full speed and rear defroster ON, this is what I get:

IDLE

Voltage at the Alternator = 13.05V
Voltage drop along ground = 0.027V = 27mV
Voltage drop along positive = 0.32V
Voltage at battery terminals = 12.7V

12.7 + 0.027 + 0.32 = approx. 13.05V (the summation of voltages above)

not happy with the 0.32V drop along the positive from alternator to battery. Note that there is zero drop from cable end to battery post (for both ground and positive), meaning no bad connection.

The same test repeated but engine running at 2000RPM (full load, all consumers the same)

Voltage at the Alternator = 13.95V.



Now, all the consumers were switched off (just engine running, no lights, no blower, no defroster):

@IDLE voltage at alternator = 14.00V
@2000RPM voltage at alternator = 14.10V.



Next test was to do with running the engine with and without battery with NO LOAD:

@IDLE

with battery connected, alternator voltage = 14.00V (as in the test above),
without battery connected, alternator voltage = oscillates a lot up to 14.5V
@2000RPM

with battery connected, alternator voltage = 14.10V (as in the test above),
without battery connected, alternator voltage = oscillates a lot up to 14.5V.


Looking at the first test above, when most consumers are on AND engine speed is around 2000RPM the voltage AT the alternator output is 13.95V. That does sound OK. However, I am not happy with voltage drop of over 0.3V along the positive cable running from the alternator to the starter to the battery.

For my theories on this, please read the next post.

 

Basically, my theory is that voltage goes downhill with the temperature.

I have noticed that when I start the car in a cold morning and go along highway, the voltage will start from a pretty much stable 14.4V and will degrade over the length of drive to below 14.0V, with same engine RPM. Once I get into traffic, the voltage will degrade even further, to as low as 13.5V, like around the city.
Now you might say it is because of lower engine speed. But even if I return to highway the voltage will not immediately jump up, but increase slowly, over period of time, like 5-10 minutes. It looks like there is a definite correlation where the alternator "degrades" with temperature, which makes sense as well, as there is a reason for the internal fan that cools the alternator down.

My theory is that if there IS a considerable degradation of the alternator capability with the temperature, it might be due to one of these effects:

1. with increasing temperature, the (already badly worn sliprings) are unable to conduct necessary field current for the demand at hand (hence why I ordered the sliprings),
2. with increasing temperature, the rectifier diodes are affected,
3. with increasing temperature, the rotor and stator windings start increasing in resistance (a fact) which adversely affects current delivery (and voltage) capabilities of the alternator.

I also think that I MIGHT help the alternator cool down a bit more by removing all the grease (since days when front of the engine was leaking oil, not any more, fixed) and dirt around the windings. Once the sliprings arrive, I will dismantle alternator (again) and give it a good clean.

Any opinions on my theories? Anyone?

Plan: Change sliprings and clean/degrease entire alternator. Re-test.
Note: the diode bridge was entirely out and disconnected from the stator last time I completely dismantled the alternator. All 6 diodes tested OK.

 

You do have to remember that right after starting the alt is working to replenish energy loss due to starting and as you drive the regulator backs off the amount of energy needed to charge the battery.

 

Good point, but do we know that these aternators are “smart” and will decrease voltage (and therefore charging current) as battery demands. I didn’t find any evidence of that in WIS. VR used in this particular car is the simple one that has no communication to ECU. It does everything internally.

It gets awoken by the SAM via L terminal, and only outputs load duty to ECU via DFM. I don’t think it is controlled in any way by the ECU.

 

It has nothing to do with being "smart". Voltage regulators have been doing this since the first dynamo was attached to a vehicle! Today they are more sophisticated than years ago but they are basically doing the same thing: keeping the battery charged but not over charged.

 

Nothing wrong with the regulator. Check the rotor windings of the alternator, slip rings, brushes, and the output voltage (open circuit ) with a scope.

The voltage output can swing between 13.5 and 14.5 or the rating of the VR so that the battery is not overcharged and dried up. You do have a "sense" wire through D+.

There may be temperature compensation within the regulator circuitry as the battery float charge voltage levels will change over temperature.

Check the terminal where the alternator B+ output terminates. Usually the connection gets loosen up slight;y and gets more resistive.

 

How many wires terminate on B+ terminal of the alternator ? One or two (red + black) ?

How about D+ How many wires terminates on D+ ?

 

This particular alternator only has 4 external “connections”:

- ground, via alternator body,
- positive aka B+, thick cable leading away from alternator, going to starter then directly to the battery!
- L terminal, controlled by SAM to wake up alternator and provide feedback that it IS running (both according to WIS),
- DFM signal out only, that tells directly to ECU about alternator usage/load.

The last two signals are thin wires via connector. I believe the attached photo is the most correct regulator version. Note that other signals labelled on the pic are just internal to the alternator.

In effect, there are just ground, thick battery charge cable and L + DFM on the connector that go to the “outside” world relative to the alternator.

 

So, you did not do a test with the battery disconnected and WITH a load? I would be interested to see if the voltage dropped by the same amount with and without the battery connected. If so, then you can rule out the battery as being an issue.

I think you theories about heat are well founded. Keep us posted how it turns out when you clean it and replace the sliprings. And you are not being a perfectionist on this issue - the engine should not drop idle speed when raising and lowering a window. The hydraulic pump on the cabriolet pulls more amps than the window regulator motor, and mine never cause any changes in idle when operating the soft top.

 

Thanks for the comments Rodney. I will re-test with the battery off and loaded, at idle and 2k.

I must use my free time that I still have it. after next weekend I am off to asia where my wife is already gone month ago back to birth city. After we come back, there won’t be this much time for playing around. :smile

 

As suspected, engine is not too happy to run at reduced voltage. when alternator is disconnected, engine runs with 12.1V and definitely shakes more, not a huge difference, but still noticeable. It may not be too evident from the video, but in person you can definitely notice the difference. I switch on the alternator at about 30seconds into the video. You can hear a drop in rpm where the alternator wakes up and puts retard torque onto the engine.

 

If your car is a 2002 CLK320, and more or less the same as the USA version in terms of power distribution wiring, and grounding, I looked up the schematics for charging circuit, and

1) The B+ cable goes to starter and then not to the battery directly. It is supposed to go to X4 terminal block (in the USA driver's footwell location), THEN to battery. At X4, there is supposed to be a capacitor between the B+ and ground to help get rid of ripples. You can have corrosion on the starter terminal which may introduce some voltage drop, as well as the X4 terminal (loose connection too).

2) The diagram shows that the Control port with two connections end up at the Instrument panel. One wire goes directly, the other goes via the K40 relay. Your car may have a different VR and wiring which is not totally unusual between markets.

3) It is not really a good idea to remove the battery while the car is running. This is not a 70's car. The output of the alternator has ripples due to three-phase a/c rectification, and the peaks can easily exceed the operating upper range of most of the modules (14 Volts). Not only you may see malfunctions, you may actually burn a module or two in the process, especially if the regulator is not behaving well.

4) The charging point (X12) is also wired to X4, so X4 terminal is the hub of power for your car. If you are measuring the voltage at that level, it may be due to the same voltage drop on X4.

 

I think you might be looking at wrong set of schematics. It sounds like w208. Mine is w209, one of the very first ones.
Correct schematic attached.

Note: U12 = left hand drive, U13 = right hand drive (mine),
so in effect cable on my car should have inbuilt (into the cable) 175A fuse (may not be visible properly on the screenshot).
WIS says: F56 - Starter, alternator fuse (in wiring harness)

P.S. Looks like even alternator setups are different for W208 and W209. W209 only has 6 diodes, where w208 has 9.

 

I must say that I am under impression now that I am chasing ghosts with this voltage "instability". I now believe that there is nothing wrong with the alternator and that voltage indeed is supposed to "fluctuate" between 13.5V and 14.5V, just as the WIS suggests!!!

There are three reasons for this:
1. because WIS says so (gotta believe the people who made the car, they know the best, don't they?)
2. I have tested and done everything possible about the alternator and VR. oh, did I mention I received the other VR and installed it? see below
3. I drove the car today for half an hour with full load, lights on, rear defroster on, blower full speed. Voltage dropped and stayed around 13.5V. And guess what. The car ran perfectly fine (this time around). It was screaming with power and no engine pinging, despite very low voltage. Transmission didn't shift as good as it can sometimes, but that might be different issue.

I am still not sure about idle suffering when closing windows or switching any sudden electrical load, and I still don't accept it as normal. However, I am now thinking that my issue of engine pinging under high load and loss of power might be related to something completely unrelated to battery voltage.

Many things come to my mind, such as:

- EGR valve (although replaced recently, another one of those Ebay deals too good to be true). Something was strange with this valve even when I received it brand new. Namely, even in the valve off position (diaphragm NOT operated by vacuum), I could blow and suck the air either direction. Although it was a slight leak, it should be completely air tight in off position, shouldn't it???
- any other possible leakage to do with getting unmetered air (replaced all ventilation hoses recently, and anyway they shouldn't have any effect during WOT, except the thick one, which IS WOT crankcase ventilation),
- brake booster vacuum leak (intermittent ???)
- intake manifold gasket leak (unheard of on this engine I think)
- intake manifold flaps issues, sticking perhaps???
- MAP (while diagnosing MAF, I had driven the car on MAP only, and it ran with some serious hesitation and stumbling). Question, while running on MAP only with MAF completely disconnected, should car run more or less perfectly, or is some stumbling expected???
- secondary air induction issue, leak,
- ECU that is playing up (I sincerely hope this is not the case, but it could be. At my job we work with programmable controllers, and they CAN play up, meaning they are still working but not in an optimal manner, even sluggish, I know all about that unfortunately)
- engine mechanical issues??? (replaced all valve lifters recently with INA and also chain tensioner, about to do the timing chain. I know, should have done together with lifters)
- fuel pressure issues (fuel pump was replaced 8 months ago by a shop, don't know what pump they put in, but fuel filter was replaced with Mahle), besides, I have driven the car around while monitoring fuel pressure via gauge, and that doesn't seem to be the issue.

Anything else that I missed??? If it is not written here, then its probably because it was replaced/fixed alredy. Any suggestions on what to tackle on first?

For your easy answering to my questions, here I will repeat the questions from the main body of the text:

1. EGR valve should be completely air tight in off position, shouldn't it???
2. While running on MAP only with MAF completely disconnected, should car run more or less perfectly, or is some stumbling expected???
3. Anything else that I missed in the list above?
4. Any suggestions on what to tackle on first?

 

1. EGR valve should be completely air tight in off position, shouldn't it???
2. While running on MAP only with MAF completely disconnected, should car run more or less perfectly, or is some stumbling expected???
3. Anything else that I missed in the list above?
4. Any suggestions on what to tackle on first?

1. Yes
2. MAP sensor is not used for mixture formation. It is there to monitor EGR flow.
3. STFT and LTFT values from OBDII scanner. Complete vehicle scan with SDS or equivalent.
4. Voltage drop between alternator B+ stud (not cable) and positive battery post (not clamp). Repeat same on negative side. Pull injector fuse out and load it with the starter. Nice long crank using tip start.

 

You ask a lot of questions regarding the performance of your car and I think you are looking at the wrong place to start.

1) You should really scan the car for faults.... Every module. Do not think every fault is reported and displayed as Check Engine Light, or pending codes.

2) Many modules have voltage regulation and supervision functions. I know that because I was having undervoltage / overvoltage issues with a bad battery in the past.

3) Many devices (sensors, senders, solenoids, actuators) work with a derived voltage from the driving modules. Typically 5V is used for many sensors, senders and it is well regulated. It does not matter if the battery voltage is 12V or 14V. Most of the modules are rated between 11 and 14V at thier inputs, so their behavior should not change at all when the voltage dips to 13V from 14V.

4) Yes the charging voltage will fluctuate, the design is supposed to keep the battery voltage at float levels (after fully charging) so that the battery will not overcharge and dry up and die prematurely. If the alternator continuously kept the charging voltage at the full rated voltage (14.5 or 14.1 depending on the alternator and car battery), overcharging would occur.

Regarding the MAF / MAP issue. If you have M112, the engine runs on MAF, not MAP. If MAF is taken out, the ECU knows this and starts running the car based on a lookup table based on engine load throttle position angle etc. It is normal for the engine not to run perfect under this condition, else why would one need a MAF ?

After installing a new MAF, the ECU must be reset. Many people do not do that, and then they blame the MAF.

 

Ignoring all other "symptoms", let's go back to the initial complaint:

Engine idle slows and lights dim when operating certain electrical consumers (such as the power windows)

This is not normal behavior. There are a few potential causes for this. One, if the alternator is bad, it could be "loading up" the engine when demand for power goes up. At idle speed, this would be noticeable. Another is that there is a wiring problem (such as corrosion at electrical connections) and that is causing excessive resistance. At idle, the alternator is not able to provide enough power to overcome this and the engine idle speed drops because the coils and injectors are being starved of power.

 

Received the sliprings today. Will also order two alternator bearings.

So, in the end, the following will have been replaced (with new parts):

- drive side bearing,
- slipring side bearing,
- sliprings,
- voltage regulator,
- stator, rotor and other parts degreased.

In many books, that is full alternator reconditioning and should last for long time to come.
Note, the rectifier bridge is not normally "wear" item, and should only need to be replaced if failed. In fact, VR is also not a wear item, but its brushes are. You can actually replace only its brushes if you wanted (part of some recondition kits).

Will replace sliprings when bearings have arrived.

If this doesn't solve the voltage "issues", then there aren't any. BTW, new Hella VR made no difference to behaviour of the alternator.
Current state of sliprings shown below.

 

Alternator partial re-con

Partial reconditioning of the alternator. Mostly cleaning out the grease and contacts.

NOTE: Stator condition after degreasing. Diodes tested for forward drop, all good, approx 0.5V each. Reverse block OK. This was confirmed with scope trace of the three phase rectified waveform. Nice and even. Diode bridge should be the last component failing anyway.

Any comments? Questions?