M5 Alternator failures. Need help!!!

[dbenson]

Board,

I am hoping you can help me from banging my head into the wheel as I am already!!

I have a 2003 M5 and I am about to install my third Alt in the car. The car seems to run well but under heavy power the DSC, BRAKE and ABS lights will illuminate, Interior climate control, NAV and sunroof will stop functioning. Once not under power, all lights return to normal and electronics operate as expected. Most recently it seems the Alt is pushing too much power to the car and is cooking my battery, which I assume is a regulator failure.

Is there a ground strap or positive lead that has been failing that could cause these erratic issues and cook my alt's regulators?

As always, any feedback is GREATLY appreciated!

db

[Pelican Parts]

The link below is to our diy tech article on the alternator removal (since you're on your 3rd one, I'm sure you know the procedure), but to answer your question about the failures; post a Comment just below the article and one of our techs will get back to you with some useful details. Hope this helps a bit and best of luck!

http://www.pelicanparts.com/BMW/tech...or_Removal.htm

[geargrinder]

Check for water or corrosion under your passenger floorboards.

Grounds are also a good call as if the voltage regulator gets erroneous signals, it can drive voltage up and cook battery as you say.

There are multiple ground straps - block to chassis, battery to chassis... Check the main one up front passenger side from block to chassis. Also triple check your alternator connections, given the multiple swaps doubtful those are 'obviously bad' but there could be something sneaky you're missing.

[ViolinARC]

Check for water or corrosion under your passenger floorboards.

Grounds are also a good call as if the voltage regulator gets erroneous signals, it can drive voltage up and cook battery as you say.

There are multiple ground straps - block to chassis, battery to chassis... Check the main one up front passenger side from block to chassis. Also triple check your alternator connections, given the multiple swaps doubtful those are 'obviously bad' but there could be something sneaky you're missing.

+1...agreed that there must be some issue inline. I would be suspect of 3 alternators failing one after the other because that ain't normal!

I had to replace the water cooled on my '00 with a re-manufactured and it's been functioning perfectly for almost 50 thousand (EDIT: ROFL at 500 mistype) miles...

The trifecta sounds like you have some loose solder in the DSC module. It could also be the iggy switch...visor test?

[chillax5]

if the problem only happens under heavy throttle, i'd check the serpentine belt isn't slipping in high RPM.

[edjack]

Monitor the battery voltage, and observe when the anomaly occurs. If an overvoltage condition occurs, it may be a clue. We've not seen reports of the results of overvoltages.

The simple thing is to use a ciggy plug and connect your DMM.

You DO live in the Rust Belt, so poor grounds can happen.

Ground shoe locations

There are several so-called "ground cable shoes" scattered around the chassis. These "shoes" terminate a few, and many ground wires. The Germans prefer the color brown for ground.

Here's where they are:


1. Two under driver seat carpet, near door threshold. X151, X173. Opposite these, X1108.

2. Left front inner fender panel. X165

3. Engine compartment, front right. X166, X1106

4. Engine compartment, right rear on outside of e-box (under the cabin air filter housing). X6454

5. Right side footwell, under carpet X490,492, X218 splice, X10012, X961


6. Right side of trunk, in battery compartment X498, X13075

7. Left side of trunk behind trim panel X13016

8. Under rear window shelf, right side X494, X18129 Splice terminal 30

Might be a good idea to inspect these shoes for tightness and cleanliness. Begin with the shoes close to the problem area.

[geargrinder]

if the problem only happens under heavy throttle, i'd check the serpentine belt isn't slipping in high RPM.

Yeah, although, 1. I have a hard time seeing how that creates an overvoltage. 2. generally even if that was happening, the battery capacity will easily mask any temporary WOT 'voltage droop' from the alternator. I once had a car blow the alternator, and I went to Walmart, bought 2 cheap extra batteries, then drove it purely on the 3 batteries for an hour and a half to the mechanic I wanted to use. Ran fine, I just watched for voltage to get too low, then swapped to the next battery.

[jclausen]

I would take it to a good independent shop and pay them some dx money, how much more money are you willing to waste on this problem

[edjack]

I was considering what the resistance of a poor ground in the alt circuit might do to regulator voltage control.

[geargrinder]

TTotally agree Ed I was responding only to the belt slip suggest.

[rdl]

Board,
...
I have a 2003 M5 and I am about to install my third Alt in the car. The car seems to run well but under heavy power the DSC, BRAKE and ABS lights will illuminate, Interior climate control, NAV and sunroof will stop functioning. Once not under power, all lights return to normal and electronics operate as expected. Most recently it seems the Alt is pushing too much power to the car and is cooking my battery, which I assume is a regulator failure.

Is there a ground strap or positive lead that has been failing that could cause these erratic issues and cook my alt's regulators?
...

Could you clarify "under heavy power". Do you mean engine power as in WOT? Or heavy electrical power as with high beams, cabin blower high, rear defogger, seat heaters, wipers, aux fan, etc. all on?

EDIT - I'm assuming electrical power in what follows, not WOT
In addition to the points mentioned above, you should consider resistance in the cable between the alternator output to the battery. Under maximum electrical power you can expect as much as a 0.5 volt drop (alternator -> battery +ve) due to unavoidable electrical resistance in the cables. But no more. If it's any more than 1/2 volt there is a problem in the power cable.

It's easy to check. Get some long wires/leads so you can measure voltage between the alternator output post and the battery +ve terminal. Wire gauge doesn't matter - you'll be measuring voltage, not current, so there will be only microamps in the voltage test circuit. Turn on every electrical consumer possible and rev engine to ~2,500 RPM so alternator is able to produce maximum amps (which it can't do at idle speed). If more than 0.5 V, the connection under the driver's seat, bottom of floorpan exposed to road dirt & the elements would be my first suspect.

With a voltage regulator integral to the alternator (as is yours) a bad ground will not drive system voltage high (which is possible with a remotely mounted VR arrangement) The alternator will deliver a constant voltage between its output post and its case. But a bad ground (or +ve power lead to the battery) will drive the car's system voltage low. The excess resistance in the fault point results in a voltage drop across it, so there is less voltage remaining/available for the car's modules.

If the +ve power lead checks out OK
Since many/all of the car's modules are affected at the same time, the engine ground strap is the first suspect for a bad ground. Duplicate the voltage measurement above, except from alternator case to battery -ve terminal. Even under maximum current draw the ground circuit drop shouldn't be more than a fraction of a volt. I don't have a number, but would be concerned if more than ~ 1/4 volt.

[dbenson]

Thank you for all of these great inputs. I am sorry was not more clear about "under heavy power". I was referring to WOT not power draw on the system.

Diving into this today with all of this input and will respond with what is found.

Again, thank you all.

db