Weird voltage issues

[sprocket2005]

Ive been having trouble with my voltage being low for a while now, what happens is that my car will be running at a closer to normal voltage reading then suddenly drop to as low as 10.8volts (according to my turbo timer) while its running. Ive got my factory boost gauge working as a battery gauge and it moves with the turbo timer, so i dont think its a faulty timer. Also, when it drops my low batt light comes on but it kinda flickers and its dim, but the low batt light does this sometimes while my turbo timer is somewhere in the low 13's still so its got me really confused and there really arent any patterns to follow, it doesnt do it more with the headlights on as compared to off, it doesnt matter if my radio is on or off, windows up or down, door or hatch open or shut, wipers on or off, fan on or off, it doesnt seem that anything i do can impact or change it. And when this happens its usually only for about 5 - 10 seconds then the voltage goes back towards the normal range but it often relapses several times, sometimes it comes back up to the low 13's then just as soon as my timer says its at about 13 it and the boost gauge drop quickly, and the low batt light does its thing too, sometimes it stays at about 13.3V for a minute or two before it drops again,
The car usually does this at idle, but it has done it driving down the road more than once, but usually it happens at idle and the rpms drop by about 100-125, im assuming from the increased load on my alt, I dont think its a bad alternator, its a brand new - 90 amp - autozone alternator. Infact its my second one, after i put the first one on and it didnt fix my problem i assumed that i got a defective alternator from autozone, so i took it back and they replaced it, I put the second one on and it seemed to improve a hair, but its still doing the same thing. I had my battery tested, and it was bad, so i got a new red top optima battery hoping to fix the problem, but it still is just as bad the battery didnt seem to help or hurt the situation at all. Im not sure what else to do so i went to every parts store within a 40 mile radius and got everything tested.

These are the results from the last parts store i went to - Battery test: Voltage: 12.73 Measured: 871 CCA Rated: 720 CCA Temperature: 107 deg. Fah. - Starter test: Voltage: 11.44 Amps: 137.0 Time: 812mS Charging system test: no load - 13.88V, 19.0V loaded - 13.92V, 37.6A Drain test: .06A

If everything in the charging system is good then how could i have a problem? It doesnt take a minute for the alternator to warm up or anything as soon as i start it its in the low 13's on my turbo timer, is it possible that my alternator could be causing my problem because of the fact its a canadian 90 amp instead of the U.S. 75 amp?

 

[Tropical Lime]

I read that your dash's light goes ON, so I assume this is the only problem.

Comparing your voltage readings to my readings, your charging system has better numbers than mine, but my battery charging light does not turn ON. Using a digital voltmeter, I get the following readings (directly from the battery itself):

* 12.45 Volts DC before starting the car
* 14 VDC at idle with only the headlights on dim (Canadian specification) in daylight running mode, parking/running lights OFF
* 13.3 V at idle with all accessories ON - rear defrost ON, fan on highest setting, headlights ON, parking lights ON, radio ON & driver door open with compartment light ON

Details:
* Canadian version, 1995 Talon TSi AWD 5spd with stock 90Amp alternator
* Still the original alternator that came with car - I know as I bought the car new on January 1995 and am the first owner
* 126,600Km or approximately 78,500 miles on the original alternator
* Idle RPM is 750RPM
* Engine is hot
* Battery is a month old Costco battery rated at 640CCA at CAN$77
* Being a digital voltmeter, a reading like 14.14V quickly fluctuates to 13.93V, then to 14.01V and then 14.14V within fractions of a second due to the digital voltmeter's fast response times. In other words, the above readings are averaged out.

Please note that the shop manual (yes, I bought one when I bought the car) says to:
* Disconnect the negative battery cable
* Connect a digital voltmeter between ground and the "S" terminal on the alternator
* Reconnect the negative battery terminal cable
* Start your engine, turn off all accessories
* Increase engine speed to 2,500RPM

At 68 Fahrenheit (SP?), the voltmeter should read 13.9V to 14.9V
At 140 Fahrenheit, the voltmeter should read 13.4V to 14.5V

I am guessing that at 104 Fahrenheit that you should be above 13.65V to be within spec, and you have 13.88V, but at what RPM?

It appears that the hotter the ambient air temps, the lower the alternator's voltage output.

What are volt readings at 2,500RPM?

 

[luv2rallye]

... is it possible that my alternator could be causing my problem because of the fact its a canadian 90 amp instead of the U.S. 75 amp?

Not because of that (unless they put a 2 wire to ECU NT one in which doesn't have a regulator in it - turbo ones have 4 wires and a regulator) but rather because you got it at an autostore which has a huge reputation of selling bad alts. Just search this forum and you will see - many had to return it 3-4 times. You already returned it once. Isn't it nice having a free replacement policy when you have to do all the getting and replacing over and over and ...

 

[Defiant]

Jesus. The alternator's dead. Probably from worn-out slip ring brushes. Replace, again.

 

[sprocket2005]

Alternator?? Maybe, but im not convinced, i had them test it before i took it home and i also had advance auto test it on my way home and both autozone and advance auto said it was good. If i were to replace it where is the best place to get a good alternator? OEM??