Alternator woes - Page 2 - PeachParts Mercedes-Benz Forum

Zulfiqar · #16 03-01-2013, 12:11 PM

the bosch 2 wire internal regulator alts require that bulb to excite the alternator circuit - a minimum of 3 watts bulb is specced.

If the alt warning light keeps glowing after engine start then the alternator is not working - test the D pin (thin blue wire that goes to bulb) directly with a test lamp with blue wire disconnected from it. The alternator should kick start itself. If not then remove the regulator and inspect.

The regulator takes ground from one mounting screw and positive from the spring clip inside the cavity. Check that they are clean. I have experienced one alternator whose regulator ground was completely corroded to the point to screw head was missing.

btw if your alternator has the W port dont test that its an internal connection before the diode pack - The only use of it Ive seen was the old VW 1.6 diesel tach pickup.

Jadavis · #17 03-01-2013, 02:04 PM

Quote:

Originally Posted by Jadavis

OK, one at a time:
The bulb/idiot light is the same one that worked for years before I had any problems. It still works now.

Edit: Fixed it. The bulb works and has always worked. I accidentally wrote "not" instead of "now".

Quote:

Loss of ground: I need to run a test wire from the battery ground terminal to the casing of the alternator, then start the car and see if it starts charging. (I like this one!) I also can/need to check ground from the alternator case to chassis. (Also easy.)

I ran a long jumper cable from the battery ground terminal to the front of the car and checked resistance from the cable to the alternator case. It read 1 ohm. The alternator case has a good ground connection.
I went ahead and connected the jumper cable to the alternator case and started the car. No change, still not charging.

Next step is to go after the excitation line from the lamp to the alternator to see if it is getting something less than battery voltage with the key in the run position.

Jim

Holmesuser01 · #18 03-01-2013, 02:22 PM

We're keeping the old fingers crossed for you... Fixing it yourself is always GREAT!!

Jadavis · #19 03-01-2013, 02:34 PM

Armchair analysis tells me that the light on the dash would not come on unless there was a complete path from the bulb to ground. Is the blue wire going to the right place on the alternator? Is it grounded to the alternator case instead of going to the field to provide initial excitiation voltage? Is the "new" regulator broken or installed wrong?

Only further checks will tell.

Jim

Jadavis · #20 03-03-2013, 03:53 PM

Hummm.....So 1 Volt DC on the blue wire might be a little low at the back of the alternator, right?

Now to find out why...

Jadavis · #21 03-03-2013, 05:06 PM

Ok, I ran a jumper from the back of the alternator to the trunk (S350D, the battery is in the trunk), started the car, and then touched the wire (attached to a screw driver) to the positive terminal. You could hear the change in the engine! It dropped RPM for a second and then came right back up. I disconnected the wire and then went up front to check my cigar lighter volt meter. 12.5 Vdc.

I sat down and gave it a couple of hundred of RPM. The voltage jumped up to 13.8 Vdc!

I took it for a spin, bought some diesel, got a car wash and then went home. Voltage stayed between 13.8 to 14.2 Vdc. As long as you keep it running the alternator works. As soon as you shut it down I assume you have to start over.

It is definately the blue wire!

Going to be a pain to fix, but I NOW KNOW WHAT THE PROBLEM IS!

Thanks everyone!

I'll post more as I figure this out.

Jim

Jadavis · #22 03-03-2013, 06:22 PM

I went out to pull the car back up on the ramp to keep working and noticed that it is charging just fine.

No idiot light.

Voltage is 13.8 to 14.2 Vdc while driving. Usually 14.0.

I'm so confused! I guess I should just be happy.

Did the alternator really just need a jump start after putting in the new regulator? Is it that simple? Why would this help/matter?

Jim

Jadavis · #23 03-07-2013, 10:24 AM

Four days and the alternator is still working fine.
Alternator does not charge the battery after replacing the regulator? Charge the paddles and give it a shock! I don't know why it worked, but it did.

Jim

studjuice · #24 03-09-2013, 05:43 PM

could you clarify what you mean by how you ran a jumper from the back of the alternator to the trunk??

Jadavis · #25 03-11-2013, 01:28 AM

Quote:

Originally Posted by studjuice

could you clarify what you mean by how you ran a jumper from the back of the alternator to the trunk??

I attached an alligator clip to where the small wire attaches to the back of my alternator. I attached the other end of the wire to a screw driver with an insulated handle. I set the screw driver on the ground, got in the car and started it. Verified that the battery light was on and that my cigar lighter volt meter read 12.5 volts (battery voltage). I rev'd the engine a little to verify that the alternator still was not working and observed steady 12.5 Vdc. I got out of the car and went to the trunk (S350D, the battery is in the trunk) and touched the screwdriver/end of the wire to the POSITIVE terminal of the battery. The engine RPM dipped and came right back up. I set the wire/screwdriver on the ground and got back in the car. 12.5 Vdc on the cigar lighter, rev'd the engine a couple hundred RPM and the voltage went up to 13ish Vdc. I disconnected the alligator clip from the back of the alternator and took the car for a test drive.

The alternator works just fine. I don't have to jump it everytime I want to take a drive. It just works. Just like it is supposed to work.

Jim

Holmesuser01 · #26 03-11-2013, 09:43 AM

I understand your being happy now, but I am uneasy about why the car was not charging before, but is now.

I'm suspicious of the regulator. Is it a Bosch replacement or something else?

In the television repair business, I've seen semiconductors not work at all, but test good when they are hit with some voltage from another source.

The alternator regulator has semiconductors in it.

I dont want it to die on you and leave you stranded somewhere.

vstech · #27 03-11-2013, 01:00 PM

you said you took the car to a carwash... did you spray clean the alternator? pulling the jumper wire off, and reconnecting it, may have cleared up some resistance in the circuit.
or the gremlin may have found a new sucker to mess with and left you alone...

Jadavis · #28 03-11-2013, 01:02 PM

It was a new Bosch regulator from Peach Parts.

I keep the cigar lighter volt meter installed while driving and the dummy light still works. I'm also keeping the jumper in the trunk just in case.

Next time I am up under the car I will check the voltage at the connection again. It WAS 1 Vdc. I would be interested to see if it still reads that. I might still have to chase that blue wire and see if looks/tests good.

My next issue to work on is the nasty fuel tank.

Jim

Jadavis · #29 03-11-2013, 01:05 PM

Quote:

Originally Posted by vstech

you said you took the car to a carwash... did you spray clean the alternator? pulling the jumper wire off, and reconnecting it, may have cleared up some resistance in the circuit.
or the gremlin may have found a new sucker to mess with and left you alone...

Drive through automatic car wash. It did have under carrage wash and probably did spray the alternator.

Between the last two posts I think I want to move the checking the voltage up to higher on my list. I will check in a couple of weeks (first opportunity). It HAD 1 Vdc on it. I wonder even more now if that has improved. If nothing else, I will take the lead off, clean it up, coat it in battery terminal gunk, and put it back on.

Jim

Codifex Maximus · #30 03-12-2013, 01:02 AM

Sounds to me like you've got a fault in the wiring or maybe the connector on the alternator.

You're getting charging now and it may be because of vibration you're getting it. Check the connector on the alternator to make sure its clean and not damaged or faulty.

Still not ruling out regulator issues though.