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Voltage problems

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RyanGT

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Discussion starter · #1 ·
My last thread was too long im guessing so people stopped responding so making a condensed version. Here is the original. http://www.moddedmustangs.com/forums/99-04/156323-different-battery-question-alternator.html

I have good voltage at idle, 13.6 when it is warm. 14.4 if i use positive terminal to chassis ground (not neg battery). And 14.4 when i just start the car (cold battery) across battery terminals. I get low voltage when driving under load, with lights on ect; which is low 13's. Under wot i get mid to low 12's. But voltage is fine at idle. Im monitoring driving voltage through datalog, and idle voltage with a dvom.

I have replaced battery with an interstate (old one was shitty shucks battery), positive wire, negative ground wire (both 1 gauge). Didn't help at all. Im thinking it is voltage regulator with the alt? Or could it be the diodes? Or am i barking up the wrong tree? When car is warm i have about a .5 voltage drop from pos battery to pos alternator. And .5 with negative terminal to the alternator casing (ground).

And it is causing injector problems on low spikes, and with BAS turned up the car will shut off completely for 10 or so seconds. Happens with lights on mostly, if lights are off it happens with BAS turned much less frequently. With lights on i tested this theory and it happened almost immediately.
 
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Discussion starter · #3 ·
Yep, checked all grounds. Cleaned them all (wires and terminals). Then replaced the negative to chassis ground.
 
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#4 ·
i personally have seen plenty of cars and trucks that will read battery voltage between 13.1 - 13.5 at idle and 14.1-14.5 at high rpms....BUT even though your voltage readings are good, your alternator probably isnt putting out the amps it is rated at. I would do an amp test on the alternator and that would let you know if the alternator was good or not. you can do it with an amp clamp that connects to a multimeter. Yes your car will start and drive around pretty good for a little while, but while running only on battery power alone, running your lights, a/c, radio, etc.. your car will run shitty and just die.
 
Discussion starter · #5 ·
Ya its opposite for me, im getting better voltage at idle than high rpm.
 
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#6 ·
yeah, has your car been running shitty and just slowly losing battry power and dying? the alternator is more than likely the problem. at work i go on about 3 to 4 calls a week to jump start vehicles, after started i bring them in the shop, charge the battery and check the voltage....all seems fine till i test the alternator for amps and then there it is, putting out about 36 amps when the alternator is suppose to be putting out 100amps. The vehicle will run fine for 2-3 days until it cant run on battery power alone anymore.
 
Discussion starter · #7 ·
Can amp rating be tested while in car, or is that out of car testing? Dvom wont handle the amp's of the alt would it? And fry?

It is running crappy, but not enough to stall out or not run.
 
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#8 ·
it can be tested in the car of u can take it out and bring it to your local auto parts dealer like napa, autozone, carquest or somethign like that..usually they will test them and batteries for free. I am not sure about dvom, havent used that..i just use my multimeter with an amp clamp.
 
#9 ·
sounds like two different issues to me. hook up your dvom at battery with leads/alligator and see what it reads at wot, could be just the circuit the ecm is getting the reference voltage is why the difference,is the datalogged idle voltage the same as the dvom?

you can check the diodes pretty much the same way as a voltage drop test. put red lead from dvom on alt output and black on alt case. put dvom on AC volts and anything over .5v starts pointing to bad diodes. electronics do not like AC voltage
 
Discussion starter · #10 ·
Never heard of the amp clamp, any links? Multimeter= dvom (digital volt ohm meter). And you said amp can be checked in car? Don't have spare car to take it out at home. Would have to do it in the rain in the parking lot (not really wanting to do that lol).
 
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Discussion starter · #12 ·
K datalog at idle read .1-.2 at most lower than what it read at battery. And If the setting was right (wasn't labeled) i did get a reading on ac. It was ~V setting (guessing thats ac), and read 30? Not sure if that could even be right? Or possible 3.0, the bottom of the 3 doesn't work, so the decimal is probably not there also.
 
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Discussion starter · #14 ·
Hmm so if .3 it is good and if 3.0 its bad. And since my multimeter is on sucky side i can't tell which lol.

What would bad diodes cause?
 
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Discussion starter · #19 ·
I called them few days ago and they said that diode and voltage regulator testing is out of car.
 
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Discussion starter · #20 ·
Looks like ill need to take it there and pull it in parking lot and make sure :dunno
 
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