Voltage / Electrical Issue

[fourmula1]

All, looking for some insight here. I fare much better when it comes to anything mechanical but admittedly struggle fully comprehending the electrical stuff.

2003 M3 race car
90k miles
New alternator (previous one died probably because of this issue)
Optima red battery

Started having issues about 3-4 seasons ago. Battery light would flicker on and off. Became sustained at the end of one season. Beginning of the next it was off but came back and remained.
New battery last year and kept it on trickle charge for any prolonged period in garage.
New alternator a few weeks ago and battery light went away.
Main battery negative ground in truck is solid and making clean contact with chassis.
Connections on alternator are solid and clean.

Two days at Watkins Glen, attached images are traces of voltage lap by lap.

Day one starts off from idle through lap one at 14 volts and starts to drop on lap two. It is then slightly erratic from 13.1 to 13.7

Day two starts off from idle through lap one at 13.9-14.1 and drops sharply on lap two and then ranges from 12.6 to 13.6

My friends identical M3 is extremely steady at 13.5-13.7

Could this be caused by bad grounds?
Would they be the main power terminals at alternator, starter, engine bay, etc.? I'll have to look up a diagram for more locations...
Could any interior wiring gone bad be causing this (not the cleanest interior stripping, there's some brown grounds that could be bad...)

Any other insight?

Much appreciated.

[bigjae46]

Aftermarket rebuild? I'd check the regulator. I've seen rebuilds not replace the regulator which includes the brushes and springs which keeps the brushes against the stator.

OE alternators have a limited lifetime warranty. Possible you got a bad alternator.

[fourmula1]

Consistent over multiple alternators.

[sapote]

All, looking for some insight here. I fare much better when it comes to anything mechanical but admittedly struggle fully comprehending the electrical stuff.

2003 M3 race car

1) Provide the month/year build and SMG or manual gearbox so I get the exact wiring diagram.

2) the voltage waveforms after the first lap look very bad with very high ripple voltage. How did you measure these voltages -- through OBD2 port?

3) I would add a small wire with one end connected to the batt positive and the other end connect to DVM with the other lead connected to chassis GND. This is to bypass the DME and measure the batt directly.

[eacmen]

Consistent over multiple alternators.

How many alternators have you tried? As mentioned above the alts available on the market are very hit or miss. Many members on here have gone through 3+ alts.

You can diagnose bad ground with a multimeter and measure resistance between battery terminal and the various major chassis ground throughout the car.

But my guess would be the voltage regulator getting heat soaked. Maybe run the car at idle and point a heat gun at the vreg and see if the voltage drops?

[fourmula1]

1) Provide the month/year build and SMG or manual gearbox so I get the exact wiring diagram.

2) the voltage waveforms after the first lap look very bad with very high ripple voltage. How did you measure these voltages -- through OBD2 port?

3) I would add a small wire with one end connected to the batt positive and the other end connect to DVM with the other lead connected to chassis GND. This is to bypass the DME and measure the batt directly.

2003.5 manual. I’ll have to check sticker for exact month.

Yes, odb port with Aim solo 2 dl. My friends car, logged in the same manner, varies 13.5-13.7.

Ok, as a means to get a direct measurement to confirm exact voltage fluctuation?

Thank you.

[fourmula1]

How many alternators have you tried? As mentioned above the alts available on the market are very hit or miss. Many members on here have gone through 3+ alts.

You can diagnose bad ground with a multimeter and measure resistance between battery terminal and the various major chassis ground throughout the car.

But my guess would be the voltage regulator getting heat soaked. Maybe run the car at idle and point a heat gun at the vreg and see if the voltage drops?

Thanks. It certainly appears like heat soak is plausible given its dropping out after the car is fully up temperature.

[fourmula1]

1) Provide the month/year build and SMG or manual gearbox so I get the exact wiring diagram.

04/03 Manual

[Arith2]

300mV is maximum allowable spec across the system for voltage loss. Most lines shouldn't really go over 20mV. Maybe from the rear to the front you might get up to a 50mV voltage drop but other that everything should be almost nothing. The whole system typically shouldn't drop more 100-150mV. Hope this helps.

[sapote]

04/03 Manual

I think you might have a bad ignition switch contact. This contact supplies 12v to F30 fuse which supplies 12v to the alternator's regulator. A dirty pitted contact had the resistance increased with higher temperature, and this might be the issue. Remove the ignition switch and clean up all of the contacts with X-acto knife (like clean up the old time ignition breaker point). You also can diagnose this by measuring the voltage at F30 or at pin1 of the alternator connector during with engine running and it should be close to 14v.

[fourmula1]

I think you might have a bad ignition switch contact. This contact supplies 12v to F30 fuse which supplies 12v to the alternator's regulator. A dirty pitted contact had the resistance increased with higher temperature, and this might be the issue. Remove the ignition switch and clean up all of the contacts with X-acto knife (like clean up the old time ignition breaker point). You also can diagnose this by measuring the voltage at F30 or at pin1 of the alternator connector during with engine running and it should be close to 14v.

Cleaned up the switch and everything is making contact it did not resolve the issue. All of the big grounds and cables seem fine.

I am waiting on a new valeo to replace the reman-bosch. Hoping that I just got unlucky with the alternator/regulator.

A friend had a 2014ish Cayman that has some sort of voltage regulator reset..... Is this a thing in our M3s?

[sapote]

I am waiting on a new valeo to replace the reman-bosch. Hoping that I just got unlucky with the alternator/regulator.

A friend had a 2014ish Cayman that has some sort of voltage regulator reset..... Is this a thing in our M3s?

Yes, try another alternator or replace the regulator.
Never heard of voltage regulator reset for our M3.

[fourmula1]

Fresh alternator and fresh battery (red top).

It was improved. Staying at 14.1 volts for the first few laps, then fluctuating a bit 13.6-14.2. One session I got drops down to 13.2.

My friends stays absolutely stuck at 13.8 (stock battery)

Getting frustrating...I think I will slowly kill the battery/alternator. I worry that it could effect critical things like fuel pump consistency, etc.?

[eacmen]

Are you and your friend tapping battery voltage meter at the same place?

I get fluctuation in voltage as well and voltage dips when SMG pump primes.


Sent from my iPhone using Tapatalk

[fourmula1]

Are you and your friend tapping battery voltage meter at the same place?

I get fluctuation in voltage as well and voltage dips when SMG pump primes.


Sent from my iPhone using Tapatalk

Data from AIM Solo2 DLs. Taken while lapping the same track at the same time.

His is a 2003, mine is a 2003.5.
Wondering if any little brown interior cabin grounds could cause this? I might have some not making great contact?
Also thinking my light control module is mounted in a precarious place and might be vibrating a lot, could be shorting or something? Lights aren't flickering or acting weird though.
Just throwing out ideas at this point....I do not have a visceral understanding of the electrical system.

Thanks