Can't get this goddamn voltage issue fixed. Could really use help.

**Keyan** · 03-21-2013, 11:06 AM

ok, here goes.

When I start my car up in the cold mornings, my voltage goes high. Like, 15+v. Yesterday it was up to 15.8v.
As the car warms up the voltage will come down to 14.8, but it wont stay there. driving under load is about 14.5. Unless I turn on ANY loads. Turning on my blinker will make the voltage tick between 14.2 and 14.5. if i turn on my headlights and a/c fan, and load the system up the voltage will drop down to like 13.5.

if i sit in traffic, the voltage will continue to drop below 13v, ive seen it as low as 12.1.

if i get on the throttle, the voltage will go down the higher the rpms go up. if it starts at 14.5, just putting my foot to WOT will drop the voltage to 14.1, and go down as the rpms go up.

The alternator is brand new. I've had 3 alternators in the car and it has had the issue the entire time (original alt, used alt, rebuild alt)

I can't figure out what the hell is my car's problem. The alternator is SUPPOSED to put out a constant voltage no matter the load. but when i sit at a stoplight on hot days i can HEAR my fuel pump slowing down. it is a major issue.

This morning my battery light was on, but my voltage was 14.8. after about 2 minutes of driving the battery light went off.

HELP. I can't even dyno the damn thing because when it sits on the dyno everything heats up and the voltage gets so low my fuel pump cant keep up and i lose pressure.

**DrGonzo** · 03-21-2013, 11:10 AM

I first question is what all aftermarket do you have installed on the car, electrical wise?

What are you using the measure the voltage? Stock Gauge?

**Keyan** · 03-21-2013, 11:17 AM

it was being measured with an safc tapped into the ecu B+. now it is being checked with a voltmeter at the cigarette lighter since the safc has been removed. the voltage has been verified at both the battery and the alternator.

the only thing aftermarket is that my battery is in the trunk. i have a 0ga B+ wire running to a soldered connection in the engine bay where the OEM wires end. i have a 0ga ground wire running to the transmission. the OEM battery negative wires are grounded to the chasis. less a foot from the connection on the transmission

**Jimvr4** · 03-21-2013, 01:32 PM

Originally Posted by Keyan

it was being measured with an safc tapped into the ecu B+. now it is being checked with a voltmeter at the cigarette lighter since the safc has been removed. the voltage has been verified at both the battery and the alternator.

the only thing aftermarket is that my battery is in the trunk. i have a 0ga B+ wire running to a soldered connection in the engine bay where the OEM wires end. i have a 0ga ground wire running to the transmission. the OEM battery negative wires are grounded to the chasis. less a foot from the connection on the transmission

Hmm, a flag went up right there. You have a soldered 0 ga wire? It takes a MASSIVE soldering iron or a torch to flow a good connection on a wire that big. Are you confident in this connection?

**jake stealth** · 03-21-2013, 01:37 PM

Hmmm, interesting. A few thoughts: Where is the rear mounted battery grounded to? Is the relatively large ground wire between the intake manifold and the chassis firewall connected and are the connections clean? This is the main chassis-to-powertrain ground - since you have a rear mounted battery it will be the only ground path back to the powertrain - hence the alternator. Might even require an additional wire here. Perhaps a large ground wire from the battery negative back to the engine is needed?

Since things are normal when cold and get a little crazy as things warm up, it seems like something is getting warm and causing a higher than normal resistance and I'm thinking ground path.

Why not try a voltage drop test between the battery negative and the alternator housing at full load with every thing turned on? Also do a voltage drop test between the chassis firewall to the alternator housing. Even with the battery so distant I'd think about 0.3 to 0.4 volts maximum here - the lower the better. This will tell you the condition of the ground circuit. It appears that you've done an excellent installation and testing of the B+ side of things - so the ground path might not be up to spec.

It's bothersome that the voltage drops off as the engine rpm increase - -any chance the belt is slipping? Just another thought.....

Good luck and keep us informed as to what you find.

**DrGonzo** · 03-21-2013, 02:43 PM

I also have a rear mounted battery and my voltage is about 13.5 and varies. I know need to beef up my ground as I am sure that is what is causing the spikes and lower than normal voltage drops at times. I have a 0 gauge wire also but I have a clamp lug on mine. Jim is right that soldering that large of a wire is not a good idea as it would take a torch to heat it up enough for solid flow.

I intend on running a 4/8 gauge wire from the battery, up to the front and making a grounding block to see if that alleviates the grounding/power issues.

**BlackStealth** · 03-21-2013, 05:30 PM

Originally Posted by Keyan

I've had 3 alternators in the car and it has had the issue the entire time (original alt, used alt, rebuild alt)
...I can't figure out what the hell is my car's problem. The alternator is SUPPOSED to put out a constant voltage no matter the load.

Actually the alternator is NOT suppose to put out a constant voltage. Temperature plays a big role, and the charging voltage is higher for cold temperatures, and lower voltage for hot temperatures. There is a charging voltage chart in the factory service manual if you want to know the exact values. Also, there's a wire with a brown connector that plugs into the alternator -- I believe this wire has a role in changing the charging characteristic of the alternator.

**stealthee** · 03-21-2013, 05:55 PM

The voltage will always vary when the turn signal is on. Its a quick spike that the alternator can't maintain.

My charging system acts a lot like yours does, except it rarely drops below 12.5 volts, but my battery is in the stock location. The way things are acting isn't really that odd.