Hi everyone, since i got my 91 coupe 3 years ago, i've noteced drop in voltage at the dash gauge when ac is on and headlights on idle, today i tested the alternater at auto zone on the car and it showed bad regulater, i bought remanifactuered one and hade them check it before i put it in the car and it passed the test and the actual voltage showed 15.29 v, i had them check the old one and it showed pass with 14.82, i still kept the new one because i hopped it will make it better, so i put it in the car and tried it with full load, and its still the same, i hooked my aldl cable and scanned it with tunerpro, it showed with load on idle 12.2 and on reverse 11.6 v!!! and driving on the freeway with 1800 rpm and 72 m/h was around 13.4 only!!! is there some thing else control the charging system beside the alternater? where do i need to look?

 

....... I saw some data that was very curious around the middle of the page ... you should get that checked out ..............

 

Battery Voltage Voltage At Fuel Pump Vehicle Speed Engine Speed
Volts Volts MPH RPM
12.5 12.6 0 675
12.4 12.6 0 675
12.4 12.6 0 650
12.4 12.6 0 675
12.5 12.6 0 675
12.4 12.6 0 650
12.5 12.6 0 675
12.4 12.6 0 650
12.4 12.6 0 675
12.4 12.6 0 650
12.5 12.6 0 675
12.4 12.6 0 675
12.4 12.6 0 675
12.4 12.6 0 675
12.5 12.6 0 650
12.4 12.6 0 675
12.4 12.6 0 650
12.4 12.5 0 650
12.3 12.6 0 675
12.2 12.4 0 650
12.3 12.4 0 650
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.3 0 650
12.2 12.4 0 675
12.2 12.4 0 650
12.3 12.4 0 675
12.3 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 650
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 675
12.2 12.4 0 650
12.2 12.3 0 650
12.2 12.4 0 675
12.1 12.2 0 675
12.1 12.2 0 675
12.2 12.2 0 675
12.1 12.2 0 675
12 12.2 0 650
12.1 12.2 0 650
11.5 12.1 0 625
11.4 12 0 575
11.5 12 0 575
11.5 11.9 0 575
11.4 11.9 0 575
11.5 11.9 0 600
11.5 12 2 650
11.5 12 2 625
11.5 12 2 625
11.5 11.9 2 600
11.4 11.9 2 575
11.8 12 0 575
12 12.1 0 575
12.2 12.3 0 875
12.2 12.4 0 1025
12.3 12.4 0 1000
12.4 12.5 3 1225
12.4 12.6 4 1300
12.5 12.7 8 1350
12.5 12.7 9 1375
12.4 12.5 10 1050
12.4 12.5 10 1000
12.2 12.3 8 650
12.2 12.3 7 700
11.6 12.1 0 700
11.5 12 0 550
11.5 12.1 0 650
11.8 12.4 0 1125
11.9 12.4 0 1175
11.8 12.4 2 950
11.5 12.1 3 625
11.5 12 3 625
11.7 12.2 0 950
11.8 12.4 0 1300
11.5 12.1 0 575
11.6 12.2 1 650
11.5 12 0 650
11.9 12.1 0 600
12 12.1 0 600
12 12.1 3 675
12 12.1 4 675
11.8 12 3 575
11.9 12 3 575
11.9 12.1 2 650
12 12.1 2 650
12 12.1 2 650
1.7 4.2 1 650
11.9 12.1 1 625
11.9 12.1 1 600
11.9 12 1 600
12 12.1 2 675
12 12.1 2 650
12 12.2 2 625
12 12.2 3 625
12 12.2 3 675
12.3 12.6 9 1575
12.2 12.4 14 750
12.2 12.3 13 700
12.1 12.3 11 700
12.1 12.2 9 675
12.1 12.2 9 675
12.1 12.2 7 725
11.9 12 1 575
11.9 12 1 575
11.9 12 1 575
11.8 12 0 600
11.9 12 0 600
11.8 12 0 600
11.8 11.9 0 600
11.7 11.9 0 600
11.7 11.9 0 575
11.8 11.8 0 575
11.8 11.8 0 600
11.9 12 0 575
11.9 12 0 600
11.9 12 0 600
11.9 12 0 600
11.9 12 0 575
11.8 12 0 575
11.8 12 0 600
11.8 12 0 575
11.9 12 0 575
11.9 12 0 600
11.9 12 0 575
11.9 12 0 575
11.9 12 0 600
11.9 12 0 575
11.8 12 0 600
12 12.2 0 725
12.2 12.3 1 900
12.2 12.4 1 975
12.4 12.6 8 1175
12.4 12.6 9 1175
12.4 12.5 10 925
12.6 12.9 18 2275
12.8 13 24 1900
12.7 13 26 1675
12.9 13 26 1675
12.9 13 26 1650
12.5 12.9 25 1250
12.1 12.5 19 725
12 12.5 18 725
12.3 12.5 15 700
12 12.4 15 700
12 12.3 14 700
11.9 12.3 9 700
12.1 12.2 5 650
11.8 12.2 4 650
11.8 12.2 3 650
12 12.2 2 675
12 12.2 2 650
11.7 12.2 2 650
11.7 12.1 0 600
11.6 12 0 625
11.6 12 0 600
11.6 12 0 600
11.9 12 0 600
11.6 12 0 575
11.6 12 0 575
11.6 11.9 0 550
11.6 11.9 0 575
11.6 11.9 0 575
11.6 11.9 0 575
11.9 11.9 0 575
11.6 11.9 0 550
11.6 11.9 0 575
11.7 11.9 0 575
11.5 11.9 0 575
11.6 11.9 0 575
11.6 11.9 0 575
11.5 11.9 0 575
11.5 11.9 0 550
11.5 11.9 0 600
11.8 12 0 600
11.8 12 0 600
11.8 12 0 575
11.8 12 0 600
11.9 12.1 0 575
11.9 12.1 0 625
12 12.2 0 725
12.3 12.4 4 1100
12.4 12.6 11 1575
12.4 12.6 12 1600
12.4 12.6 12 1700
12.5 12.7 16 1925
12.5 12.7 17 2025
12.6 12.9 31 2275
12.3 12.8 35 2300
12.4 12.8 36 2375
12.4 13 51 2275
12.4 12.9 52 2125
12.9 13.1 67 1650
12.8 13.1 67 1675
12.8 13 66 1525
12.5 12.9 60 1400
12.5 13 61 1875
12.7 13.1 61 2250
12.6 13 65 2700
12.8 13 66 2700
12.8 13.1 67 2725
12.9 13.2 68 1700
13.2 13.5 67 1650
13.3 13.5 66 1650
13.2 13.5 66 1650
13.2 13.5 66 1625
13.2 13.5 67 1650
13.2 13.5 67 1675
13.2 13.5 68 1700
13.2 13.5 68 1675
13.2 13.5 71 2250
13.2 13.5 71 1800
13.2 13.5 70 1750
13.2 13.5 69 1725
13.2 13.5 67 1650
12.9 13.5 66 1650
13.3 13.5 65 1450
13.3 13.5 62 1550
13.4 13.5 61 1525
13.3 13.5 61 1500
13.1 13.5 61 1525
13.3 13.5 63 1550
13.3 13.5 63 1550
13.3 13.5 64 1600
13.3 13.5 64 1600
13.3 13.5 63 1575
13.3 13.6 64 1600
13.3 13.5 64 1600
13.3 13.5 64 1600
13.3 13.5 64 1600
13.4 13.6 64 1600
13.3 13.5 64 1600
13.1 13.5 63 1550
13.1 13.5 63 1600
13.3 13.6 75 1825
13.4 13.6 74 1875
13.3 13.6 74 1850
13.4 13.6 74 1825
13.4 13.6 75 1850
13.3 13.6 75 1850
13.4 13.6 75 1850
13.3 13.6 72 1775
13.3 13.6 72 1775
13.4 13.6 71 1750
13.3 13.6 71 1775
13.3 13.6 71 1750
13.3 13.6 71 1750
13.3 13.6 71 1750
13.3 13.6 71 1750
13.2 13.6 72 1775
13.3 13.6 75 2675
13.2 13.6 75 2700
13.2 13.6 76 2650
13.3 13.6 75 1825
13.4 13.6 74 1850
13.4 13.6 72 1600
13.3 13.6 70 1600
13.4 13.6 70 1725
13.3 13.6 70 1750
13.4 13.6 69 1725
13.4 13.6 69 1700
13.3 13.5 69 1700
13.4 13.6 68 1675
13.4 13.6 68 1700
13.4 13.6 68 1650
13.4 13.6 68 1650
13.4 13.6 68 1675
13.4 13.6 68 1700
13.3 13.6 68 1675
13.3 13.6 68 1675
13.3 13.6 69 1675
13.3 13.6 69 1675
13.4 13.6 68 1700
13.4 13.6 69 1700
13.4 13.6 68 1725
13.4 13.6 69 1675
13.4 13.6 68 1700
13.4 13.6 68 1650
13.3 13.6 68 1700
13.4 13.6 68 1700
13.4 13.6 68 1675
13.3 13.6 69 1700
13.4 13.6 68 1675
13.3 13.6 69 1725
13.4 13.6 69 1700
13.3 13.6 70 1750
13.3 13.6 70 1725
13.4 13.6 70 1700
13.4 13.6 69 1725
13.4 13.6 70 1725
13.4 13.6 69 1725
13.4 13.6 70 1700
13.4 13.6 69 1750
13.3 13.6 69 1725
13.3 13.6 74 1825
13.4 13.6 74 1850
13.4 13.6 75 1825
13.4 13.6 74 1825
13.3 13.6 74 1825
13.4 13.6 74 1800
13.3 13.6 73 1825
13.4 13.6 73 1800
13.4 13.6 72 1775
13.4 13.6 72 1800
13.4 13.6 71 1750
13.3 13.6 71 1775
13.3 13.6 71 1775
13.3 13.6 71 1800
13.4 13.6 72 1775
13.3 13.6 78 3075
13.1 13.6 79 3150
13 13.6 79 3100
13.4 13.6 83 2375
13.4 13.6 83 2025
13.4 13.6 82 2000
13.4 13.6 77 1925
13.4 13.6 76 1875
13.4 13.6 76 1875
13.5 13.7 75 1875
13.4 13.7 74 1875
13.4 13.6 75 1850
13.5 13.6 74 1850
13.4 13.6 74 1825
13.4 13.6 74 1825
13.3 13.6 74 1850
13.4 13.6 75 1850
13.4 13.6 75 1850
13.3 13.6 76 1850
13.4 13.6 76 1900
13.4 13.7 71 1750
13.4 13.7 71 1775
13.1 13.6 72 1750
13.2 13.7 71 1775
13.2 13.7 71 1725
13.2 13.6 70 1725
13.2 13.6 69 1725
13.4 13.6 66 1625
13.4 13.7 65 1650
13.4 13.7 69 1700
13.5 13.7 69 1700
13.4 13.7 69 1700
13.5 13.6 68 1700
13.4 13.6 69 1700
13.4 13.7 68 1700
13.5 13.7 68 1700
13.4 13.7 67 1650
13.4 13.7 67 1650
13.5 13.7 67 1675
13.4 13.7 67 1675
13.3 13.7 68 1650
13.4 13.6 69 1725
13.4 13.7 67 1625
13.4 13.7 67 1650
13.4 13.6 68 1675
13.2 13.7 66 1625
13.2 13.7 65 1600
13.2 13.7 65 1600
13.4 13.7 65 1625
13.2 13.7 64 1600
13.4 13.7 64 1550
13.3 13.7 63 1550
13.5 13.7 63 1550
13.4 13.7 63 1575
13.3 13.7 64 1600
13.3 13.7 65 1600
13.5 13.6 66 1600
13.4 13.7 65 1625
13.5 13.6 68 1650
13.4 13.6 67 1700
13.4 13.6 68 1700
13.4 13.7 68 1700
13.4 13.6 69 1700
13.4 13.7 68 1700
13.5 13.7 67 1650
13.5 13.7 66 1650
13.5 13.7 66 1650
13.5 13.7 66 1625
13.4 13.7 65 1600
13.4 13.7 63 1575
13.4 13.7 63 1550
13.4 13.7 63 1550
13.5 13.7 63 1550
13.5 13.7 60 1525
13.2 13.6 61 1500
13.2 13.7 60 1500
13.1 13.7 59 1475
13.5 13.7 52 1275
13.5 13.7 50 1225
13.5 13.7 46 1175
13.5 13.7 47 1175
13.5 13.7 46 1175
13.5 13.7 46 1150
13.5 13.7 47 1150
13.5 13.7 46 1150
13.5 13.7 47 1150
13.5 13.7 46 1150
13.5 13.7 45 1025
13.5 13.7 45 1025
13.5 13.6 46 1025
13.5 13.6 43 1025
13.5 13.6 42 1000
13.5 13.6 40 975
13.4 13.6 33 775
13.5 13.6 32 800
13.5 13.6 30 775
13.5 13.6 22 650
13.4 13.6 20 675
13.5 13.6 18 700
12.1 12.2 16 725
12.2 12.3 17 725
12.3 12.6 16 1075
13.4 13.6 21 1200
13.4 13.6 20 1100
13.4 13.6 20 1075
13.4 13.6 20 1025
13.4 13.6 20 1325
13.4 13.6 20 1375
13.4 13.6 21 1375
13.4 13.6 22 1575
13.4 13.6 24 1650
13.3 13.6 25 1675
13.4 13.6 26 1650
13.4 13.6 27 1750
13.4 13.6 27 1725
13.4 13.6 27 1725
13.4 13.6 28 1250
13.4 13.6 28 1300
13.4 13.6 29 1250
13.4 13.6 30 1150
13.4 13.6 30 1100
13.4 13.6 30 1050
12.3 12.6 28 775
12.2 12.6 27 750
12.1 12.5 22 725
12.3 12.5 8 700
12 12.4 8 725
12.2 12.6 8 1075
12.7 12.8 8 1375
12.8 13.2 12 1650
13.3 13.6 16 2000
13.3 13.6 18 2175
13.4 13.6 21 1475
13.4 13.6 24 950
13.4 13.6 24 925
13.4 13.5 24 800
13.3 13.4 24 775
13.4 13.5 24 875
13.4 13.6 25 1075
13.4 13.6 26 1175
13.4 13.6 25 1175
13.4 13.6 26 1200
13.4 13.6 27 1225
13.4 13.6 27 1225
13.4 13.6 27 1200
13.4 13.6 27 1025
13.4 13.6 27 925
13.4 13.6 26 900
13.4 13.6 27 850
12.8 12.9 26 750
12.8 12.9 26 775
12.9 13.1 26 800
13 13.1 26 775
12.8 13 26 775
13 13.2 26 800
13 13.2 26 800
13 13.1 25 800
12.8 12.9 25 775
12.8 13 25 775
12.8 13 24 775
12.8 13 24 775
12.9 13 24 775
12.4 12.6 24 775
12.1 12.5 20 725
12 12.4 12 700
12 12.3 10 675
12 12.3 10 700
11.9 12.3 10 700
12.2 12.3 8 675
11.9 12.3 8 725
12 12.4 8 750
12 12.4 8 750
12.2 12.3 8 700
12.2 12.3 6 675
12.3 12.4 5 675
12.2 12.4 5 650
12.1 12.3 5 650
12.1 12.3 5 650
12 12.2 3 625
12.1 12.2 2 650
12.2 12.3 0 550
11.2 12.3 0 550
12.5 12.6 0 750
12.5 12.6 0 725
12.5 12.6 0 700
12.6 12.7 0 700
12.6 12.7 0 675
12.6 12.7 0 675
12.6 12.8 0 675
12.6 12.7 0 675
12.6 12.8 0 650

 

i erased it because i copied everything and it was looking kind off confusing, but i just posted now another one

 

When my alternator went out, I bought a remanufactured one, put it on and found out it was Dead On Arrival! What a pain in the AZZ! I took it back off, and returned it for a brand new one and I haven't had a problem since then. My point is that it is possible that you got another bad one.

 

yah true, but i had them test it and it showed very good results

 

any ideas pls?

 

Yes,

get your original alternator back & then visit your local Auto Electrical Starter & Alternator repair shop.

Pay the guy $30 labor to rebuild the original.

I rebuild my own alternators & starter motors with parts purchased from my local Auto Electrical repair shop.

Guaranteed to work as it should then.

 

its the second new one today!! when i put the first one this morning and saw its the same, i went running to them and had them replace it for me with another one, put it in the car and its still the same!!! i had them check the original one and it passed the test too!! but i still kept the new one because the plastic washer on the old one that is located under the 10mm bolt broke down when i was taking it off the car and the bolt was spinning because of that so i didnt want to put it back on the car because it may shortcycle and cause a bigger problem than the $100 i paid for the new one !! so since the original one and the 2 new ones shows the same results i started thinking it may be some thing else beside the alternater

 

and how come voltage at fuel pump is higher than battery voltage? i'm suspecting wiring problem or something like that, is the ecm envolved in the charging system too?

 

this thread is interesting..

can you explain the data at the middle of the page?

is this something I should consider dropping in excel and doing the subtract column2 from column 1 and highlighting the negative answers on in red option?

 

well im not sure what should i explain, from the left its the battery voltage, next to it its the voltage at fuel pump, next to it is the vehicle speed, next to it is the rpm, its the data log file from tunerpro, i know nohing about excel

 

system voltage is constantly greater than the battery... regulator should therefor be fine, right?

everything looks ok to me?

 

Here is what a good alternator should read. First, measure the voltage on the battery terminals with a known good voltmeter. Cold, engine idling without a high electrical load (everything electrical off), the alternator will deliver 14.7 volts to the battery. The alternator output voltage drops as it comes up to operating temperature and will be 13.7 volts. If you compare the voltage on the dash voltmeter with your voltmeter, you will see the dash voltmeter lower by about 0.3 volts because it measures the voltage after the ign sw and there is normally about 0.3 volts drop across the ign sw contacts.

 

thanks i'll try that tomorrow, so 13.7 when its warm? without any load? what about with full load on idle? how much it should be? on the free way, i tried it with full load and without load, and it was showing 13.5 only in my tunerpro

 

on the stop light, with the lights on and the ac on, the signal flashes slow and tuner pro shows 11.4!!!

 

there could always be a bad connection somewhere, but if you have not done it, I would pull the battery and have it tested also.

I would also take a good look at the charging wire from the alternator to the battery. I'm out of ideas after that, tho.

Maybe someone can help here, but I think one way to check charging wire is to put a voltmeter positive lead on the alternator charging bolt and the negative lead on the positive side of the battery. The voltage displayed indicates the loss or bad connection in the wire.

this looks like a good site:
http://www.excelauto.com/online/Tech.d/altvdt.html

 

the battrey is 6 months old, i can leave the car untouched for 2 weeks and the battrey will be fine, also i had this problem since i bought the car 3 years ago, there is no way 2 new alternaters would be bad specially i had them tested before installation, must be some thing in the car,

this site looks good, i'm going to perform the test in the morning and let u guys know the results
thanks

 

In the first place, the alternator is barely working at idle. That means that anything you do at idle is invalid. You need to rev the engine up a little to get valid readings.

TunerPro does NOT show battery voltage. It displays what the ECM tells it, which is IGNITION voltage. In other words, the voltage after it goes through the ignition switch and all the other voltage drops on its way to the ECM. I think there's a fusible link in the circuit and other stuff I don't want to take the time to research.

The reason the ECM reads ignition voltage is so that is knows when you turn the key on or off. The ECM is powered all the time in "standby" mode and wakes up when you turn on the ignition and goes back to standby mode when you turn off the ignition.

 

The battery is probably fine then. However, I would fully charge it before testing again, and check for parasitic draw when the car is off, especially if you let it sit a lot normally. Let the car sit 30 minutes before testing for parasitic draw, tho. I know my car shuts off the accessory circuit after 15 or 20 minutes so that could give a false reading.

I use battery maintainers on all my vehicles that sit more than a week.

HTH