2001 AMF starting issue/Electrical problem

OleBen

OleBen

New Member
I have some strange behavior from our A2, that my girlfriend is using as a daily driver.

There are 2 problems, the first was that the starter motor almost always (bot not every time) turns over slowly/struggles to turn the engine over first TDC.

So I checked the charging, and without any load on idle, its 14,1 to 14,2V. With load it's 13,8 to 13,9V, also idle. This was measured both on alternator B+/alternator ground and battery posts.

VCDS shows no codes.

So I thought it was the battery. So I swapped it for the battery in my A3, all good. Started straight up, no problem.
Drove to the city, to deliver some stuff. And when I started the engine to go home, same problem. (But it did start) ?

So I came home, and started to look some more into it. By now it had gone darker, so I noticed that the interior lamp was dimming ever so slightly. (Problem 2)
So s**t, there goes the money for a new alternator. I hooked up the Oscilloscope to the battery (more protective for the laptop than engine bay), to see if any diodes had taken a beating, but there was no oscillation in the voltage. Had on a lot of current consumption at this point.

So I opened the door again, and the light was still dimming slightly. So checked the Scope on the battery again, but more or less stable reading.

So I hooked the scope to the interior lamp, and checked there. And yes, there was a oscillation in the voltage. And the average voltage was around 12,8V.
I then measured the power outlet in the center console, and same problem there. o_O

Checked the battery with my voltmeter, 13,9V... Checked the alternator, 13,9V...

I then checked the fuse box on the positive terminal of the battery, 13,9V.
Just to be sure, I checked the grounding cable from engine to chassis, it was holding on for dear life. I also tried to use a jumper cable between engine ground and chassis ground, but no difference.

At this point I started to think, what is consuming power. So I turned of everything that was not needed. Lights, seat heater, climate control, interior light.
The voltage started rising, but still the voltage was oscillating. Suddenly I hear that the Webasto stopped (post fan run was finished),and the voltage stopped oscillating.

So fine, there is probably something with the fan. I have a spare webasto. No big problem.

So I started to put back together everything. I had put on interior heating (in eco mode to prevent the Webasto from firing up again) and lights again to have more visual, and to charge the battery.

And when I was to remove the PC/Oscilloscope (Still connected to the interior lamp), I noticed that the voltage was going down. So again, turned off everything, and voltage started to rise. Battery voltage was still ok.

Another strange thing I noticed, when the engine was running, the voltage regulator seems to work perfectly. After start, I measured a charging current of about 25 amps and falling. Starting current was about 260A, not 100% sure as the current clamp does not have high/low memory. When loading up the alternator, it increased the current.
The strange part was that when I measured the amount of current coming from the alternator, it was lower than what was going out on the small cable(which I guess is going to a junction box of some sort) And this was not measured on max load, this was also happening when there was a small load on the system.
I will have to recheck, because it is so strange, and the ampere meter is a cheap brand.

So I have to tear apart some more of the car, to get a better overview. Good thing is that if we drive with ECO mode activated, the battery survives better. Not perfect, but better. So now I just need to figure out if voltage loss is on + or - side of the circuit.

BUT, the big question, have someone else had some similar problems?

Also, the smaller cable going from the fuse on the battery terminal fuse box, where does it end up?
Is it going to the "hole" in the floor on the left side (LHD vehicle), or is it going somewhere else?
Is there another place other than the battery terminal that the interior junction box/fuse box get's power from?
I could not find any wiring diagrams for the AMF, not sure if it is the same on petrol/others. Probably have to get if from erWin, could not find any haynes manual for the A2. I checked on Workshop-manuals.com, but could not find any wiring diagrams there.

Any help is most appreciated.

Just to summarize:
1. Hard to start.
2. Oscillation in interior lights when Webasto is running.

Have a great night! :cool:
 
The oscillation with the Webasto is just what it does, as I understand it. Mine (2002 AMF) is exactly the same. Whatever else you've got going on, you don't need to waste any time or money replacing it.

Sounds like a voltage drain going on somewhere though. Do you have anything in the 12v socket or piggybacking from its circuit? That one is permanently live.
 
Disconext positive battery cable and check amps when car is off. You will know how mutch amps (miliamps) it drains. Then you can do the same with your fuses to know where the drain is.

Also check glow plugs resistance with multimeter (you no need to remove them).
 
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The webasto during start up uses over 9 amps of draw for the glow plug - which will hit your battery if you don’t do a long enough drive to replace the charge (in a car without your issues).

Interestingly, I believe that in diesel type heaters the glow plug goes off after the burn chamber is up to temperature but appears to reheat during the cool down phase to burn off residual diesel cleanly and prevent soot. So you apparently get another peak in draw. I’ve never tested our Webastos but it does appear to happen that way in Eberspachers and the eBay diesel heaters.

So that extra sag during cool down may just be it’s normal function

Alex

Ps. Perfectly blase that you have an oscilloscope handy for this. Doesn’t everyone?


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Thanks for the replies.

I will look into it, but I do not believe that it's down to voltage drain, because I can charge battery overnight with my Bosch charger, and it starts just fine. then after driving for 30 min with normal accessories on, and performing a short stop, like top up fuel or grocery shopping, it can be hard to start. Nothing is connected to the 12V socket except if someone is charging the phone. But it is removed after charging.
If I then do the same thing with minimum accessories on, I do not have the same problem.

And the car can be parked over the weekend, and have same behavior as overnight. Not worse or better.

But I have to look into the fact that I have different voltage in 12V socket and on the battery when the load is "heavy". Minimum current while engine was running was about 12A, and maximum was about 65A. And this is well within the 120A the alternators have as max output.

So just have to find the end point of the 12V feed (30) from the battery, and take it from there.
 
Pinkythelabrat said:
The webasto during start up uses over 9 amps of draw for the glow plug - which will hit your battery if you don’t do a long enough drive to replace the charge (in a car without your issues).

Interestingly, I believe that in diesel type heaters the glow plug goes off after the burn chamber is up to temperature but appears to reheat during the cool down phase to burn off residual diesel cleanly and prevent soot. So you apparently get another peak in draw. I’ve never tested our Webastos but it does appear to happen that way in Eberspachers and the eBay diesel heaters.

So that extra sag during cool down may just be it’s normal function

Alex

Ps. Perfectly blase that you have an oscilloscope handy for this. Doesn’t everyone?


Sent from my iPhone using Tapatalk
Click to expand...
Thanks, I will look into that. Interesting to see what actually is gong on. Maybe possible to monitor in VCDS? I can't remember what values was available in measuring blocks for the aux heater.

Oscilloscope is a occupational hazard, used to work as a Field support engineer at Nissan and Tesla for a bunch of years. And sometimes you wake up at night, having an idea/solution in your head, and have to check it out before you forget it again. My residential boss was not always so pleased with it. ?
 
Regarding the starter motor i suggest to remove and clean the starter very good and also to check/clean the earth (-) cable that is connected behind the left headlight.I have the same problem and after doing this the starter was very strong.
 
Our 2005 TDI SE 75 a couple of years ago started to struggle to start, we put it down to the battery so changed it, it was ok for a few days and became just as bad...........we put up with it until a few weeks ago when I finally decided to sort out the screech sound from the starter and dropped it from the car,
I had another starter from my scrapper that I knew didn't screech but found a vid on the tube on how to take it apart so i did so and cleaned it out and re greased and fitted it to the 2005 car, since the swap it has started on the button every time, even after standing for two weeks over the christmas period.

Maybe just taking of the earth strap from behind the headlight to the starter and a thorough cleaning both ends might have solved my starter problems, I dunno, I just know that it is a different car starting wise.
 
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