Alternator or voltage regulator?

[jpspohn]

I have a replacement alternator (Bosch) in my '89 325i E30. It's between 5 and 10 years old. Lately, sometimes when I switch to high beams, my radio cuts out for a second. I've noticed when starting out, if my I lug my engine and my RPM drops low, my lights dim briefly. Now my battery is getting weaker and actually failed to start the car yesterday. (The car starts quickly usually with no long drags on the battery.) I tested the voltage at the battery with the engine running at 1500 RPMs and it measured 12.75 as opposed to 13.5 to 14.2 which is normal according to the Bentley manual. When I turn on the lights, radio, and blower, the voltage stays at 12.75. Should I replace my alternator or my voltage regulator? Anyone have an opinion? Money is an issue for me. Thanks in advance.

[Greg323i]

I would think it's the battery because the voltage seems to be there (even it's a little low) but it can't supply the current. Measure across the battery when the engine is off and see what the voltage is there and if it's slowly dropping. If the battery is fine then it will be the voltage regulator. It might also be a combination.

You posted this in the E21 section, so you might want to move it over to the E30 section before the wolves start attacking.

[Yonkers320is]

check the belt. I bought a new regulator, alternator, and that didn't fix the problem. I took it to my friends garage, he put a new belt and problem fixed.

[Houpty GT]

Most likely the voltage regulator on your car is held in by 2 philips screws. it takes about 5-10 minutes to pull and replace it. Take it out and see how long the carbon brushes are. The brushes on my old Audi last just over 200,000 miles then they started the electrically system to act up every now and then till they completely failed. As the brushes wear down they don't apply the same pressure they did when new.

Check your belt and tension.

Autozone, etc. will check your battery and alternator for free. Sometimes they do not know what they are doing so keep that im mind, but they should be able to show you if the alternator is making power or not.