LoudBimmer Posted October 2, 2013 Report Share Posted October 2, 2013 Well, I'm trying again to fix this issue. car BMW e46 325i So right now I have 260amp alternator with a xs power D3100 battery(fully charged). I also replaced belt and tensioner pulley. At 2k rpm voltage stays at 14V (normal for my car.) When ever I apply a small load, like rolling windows up, my voltage would dip down to 13.7 for a second and back to 14v. If I turn the heater on, headlights and fog lights, voltage goes down to 13.4-13.6. even if I keep my rpms@2k. WHY? If I understand it correctly, at 2k rpm alternator puts out 260amp, so a minor load should not cause a voltage drop. It doesn't look like a belt slip, since the voltage stays constant while I drive. Only when load is applied it does this. I tried using different alternator (stock) and it was doing the same exact thing. So does this mean I have a bad relay somewhere? or wtf is the problem? I had HO alternator tested and it was 100% functional. I was told that I need to get a better belt wrap to fix this issue. But seeing how even the stock was doing this, belt wrap is not an issue. What else can it be? Link to comment Share on other sites More sharing options...
Kranny Posted October 2, 2013 Report Share Posted October 2, 2013 PCM? Link to comment Share on other sites More sharing options...
LoudBimmer Posted October 2, 2013 Author Report Share Posted October 2, 2013 That's what I'm guessing too, but want to get a second opinion before I order one. Link to comment Share on other sites More sharing options...
Kyblack76 Posted October 2, 2013 Report Share Posted October 2, 2013 Order what? PCM controlled is My bet also. You may see a spike when you get wangin on your system. Id bet that isn't anything faulty. It's what you have bro. SMD SUPER SELLER The Burban Build Blazer Build sold Acura trunk build sold Link to comment Share on other sites More sharing options...
snafu Posted October 2, 2013 Report Share Posted October 2, 2013 Where are you monitoring this voltage drop? And with what? Tony Candela - SMD Sales & Marketing Email me at [email protected] to learn about becoming an SMD Partner! Link to comment Share on other sites More sharing options...
LoudBimmer Posted October 2, 2013 Author Report Share Posted October 2, 2013 I'm using a VM-1 meter plugged in the car charger and also checked it with DMM directly from alternator and in the back where battery is. I was referring to ordering new ECU(engine control unit). That's what you meant right? Link to comment Share on other sites More sharing options...
dangaranga Posted October 2, 2013 Report Share Posted October 2, 2013 They are saying that the pcm/ecm actually controls the voltage and is telling the alternator what voltage it wants under those conditions, there isn't anything wrong with the ecm/pcm it's just the way they behave. I believe the theory behind commanding a lower charge voltage is that it will lower the strain on the alt and resulting in better "fuel mileage" Brandon 2000 Furd Ranger supercab 4x4 System: welding wire throughout the truck USalts 390amp Hairpin Juicebox in stock location 8 Banks of maxwell supercaps 2 American Bass Vfl 1100.1 wired to .35 each 2 Fi Audio Sp4 18's ( the DD sc 9918's smoked) Pioneer radio with Soundstream PA mids Powered by a nice sized soundstream 2 channel It's pronounced (dain-ja rain-ja) 2001 2 door focus 1 DD9918 SC Link to comment Share on other sites More sharing options...
LoudBimmer Posted October 2, 2013 Author Report Share Posted October 2, 2013 But when I had my old alternator which burned out, I never had this issue. Only when I replaced it and tried the other 2. Link to comment Share on other sites More sharing options...
Quiet Posted October 2, 2013 Report Share Posted October 2, 2013 well, when a window motor starts (any electric motor for that matter) you'll get a surge as the motor starts. Not to mention that I'm sure that the BMW didn't go overkill on the normal internal wiring... Can you measure at the alt and verify? 2007 Pacifica Rebuild. Less quiet. Still not loud. Link to comment Share on other sites More sharing options...
tacomaguy1 Posted October 2, 2013 Report Share Posted October 2, 2013 just because you're at 2k rpm you're alternator isn't always supplying 260a like you said....only when needed I thought? Team Flex Issues Link to comment Share on other sites More sharing options...
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