Commanding more voltage from the alternator

[DSteck]

I've never messed with the alternator before. That said, I'm trying to fight an issue where I'm losing voltage at idle, which is just causing hell on my system while it tries to idle.

In the system settings... Are the Fuel System Voltage Minimum and Airflow System Voltage Minimum parameters a voltage that ends up being targeted? Currently the Fuel one is set to 12.5 and the Airflow is set to 12. Ideally, I'd like to maintain 14v at all time, but 13.8 would suffice. Having never messed with these before, I hesitate to make changes to avoid melting wiring or causing some unknown stupid ass problem.

Bueller? Bueller?...

[Shrek]

Stock alternator should output 13.5V at idle - which keeps you out of diagnostic purgatory.

Is the alternator defective ?

Is there a massive current draw of some sort ?

A Gen IV truck tune in a retrofit setup won't activate the alternator (system runs on the battery) for 2 minutes - unless the tune is reconfigured.

[flame]

A battery with poor reserve capacity can cause that too

[DSteck]

I replaced my factory alternator thinking it had gone bad (which is common in C6s). I now have a Nations 290XP alternator, which is a bad mofo. Still didn't fix it.

Keep in mind, I have the additional draw of Autometer Nexus gauges, a boost controller, and an Aeromotive Eliminator fuel pump. My electrical system is pretty taxed at idle.

I hold 14.5v no problem while driving. Idle is the only time anything weird happens. The idle will dip, which is followed by a loss of 2-3 volts. When it dips, sometimes it recovers quickly, and sometimes it stays about 100rpm low. You can hear the pump slow down when this happens. Then, all of the sudden, it'll recover, voltage comes back, and you hear the pump go back to normal. Sometimes it'll immediately dump again, and if it keeps stacking on itself, it'll draw the idle down lower. It has never stalled out. It is much worse with the AC on. I tried TR7IX plugs, which didn't fix it.

Basically, if I can force the alternator to charge full time at idle, I'm hoping it'll go away.

I replaced the battery almost a year ago, but it's possible the new battery is defective. I never have more than 11.8v when I go to start the car. However, the car can sit for a month, and will still fire up like it had just been run.

[carlrx7]

I bet its the underhood temps my tt car does the same low as 12.2v, but the auto one stays right at 14v.

Try removing the hood liner (may help airflow?), i forgot i took it off the auto one because it was all tore up form the vararam.

anyways, if it happens close to your house, let it idle and pop the hood and have a fan blow over the engine bay, bet the voltage goes back up..

-Carl

[DSteck]

It'll do it with the hood up. This Nations alternator has a big ass fan built in too.

A vented hood is still on my to do list.

[edcmat-l1]

I'd be interested to see what the actual DC (PWM) is of the alternator, and the output. Not the scan data, but with a scope.

Does the VCM scanner control L teminal on/off work for your car?

[IDRIVEAG8GT]

Does the VCM scanner control L teminal on/off work for your car?

Past C6's I've played with works fine in the scanner, and stock ones with a good charge bumble around 50-70% duty cycle at idle.

Sounds like you've got a cell going bad in the battery Dave, trucks do the same thing as well. I say this because I know all about the NAPPT series alternators and yes, they are indeed bad little bitches.

[DSteck]

I need to get off my ass and warranty this battery. I've been suspecting it may have an issue since it never has over 12v for key on.

I don't have a scope, but I could toss a voltmeter on and just see. The actual needle on the dash is incredibly slow to respond, but when logging ignition voltage, you can see it drop pretty readily.

[INTMD8]

One thing to consider is that many high amp alternators actually have significantly lower output than stock at idle rpm and only exceed a factory alternator at around 2500 engine rpm and up.

See if they can supply you with a graph of amps vs rpm for their alternator vs a stock one.

[DSteck]

Problem happened worse with my stock alternator.

[carlrx7]

try a smaller pulley if the alt can handle the rpms.

[IDRIVEAG8GT]

I need to get off my ass and warranty this battery. I've been suspecting it may have an issue since it never has over 12v for key on.

This.

[jimmyblue]

Stock, my alternator would sag at stoplights whenever
it was hot and the A/C is on. There's a load limit that
seems to pull in when the alt gets hot. After I got my fans
set up where I liked, that quit happening so much.

An alt overdrive pulley might help (or, put you into trouble at
the other end). My theory is that this is a problem with the
field current regulator self-protecting (thermal limit) when
load and engine bay temps are high - at idle, you have to
throw more field current to make up for lack of RPM.

Getting more, cooler air into the engine bay might also
help you. But to the eye, it looks like 'Vettes might suck
even worse for cooling air path than F-bodies.

[DSteck]

A vented hood is on my list. I probably should have done that before a $750 alternator. FML.

[HRD]

Had the same problem on an LS2. Had to go to a smaller pulley to fix the problem.

[carlrx7]

Had the same problem on an LS2. Had to go to a smaller pulley to fix the problem.

where did you source the smaller pulley? how many rpms were you turning?

[gn2beatu]

Keep in mind, I have the additional draw of Autometer Nexus gauges, a boost controller, and an Aeromotive Eliminator fuel pump. My electrical system is pretty taxed at idle.

Gauges dont draw hardly anything. Have you checked the voltage with a DVM at different locations? At the alternator, at the Battery, at the fuse box? I say this because allot of times a ground upgrade kit helps, along with cleaning all the existing body grounds. I like to run two additional 4ga ground cables, one from the alternator to the battery (attached to alternator case), the other one from the battery to the body. I have found the one that goes to the alternator case helps the most, as this way the current isnt being drawn through all the brackets/bolts that go to the motor.

I hold 14.5v no problem while driving. Idle is the only time anything weird happens.

Since it is RPM related, a smaller pulley would work wonders.

I tried TR7IX plugs, which didn't fix it.

Spark Plugs wont fix a voltage issue.....

I never have more than 11.8v when I go to start the car.

Is this voltage that your seeing on the gauge while cranking, or measured at the battery?

However, the car can sit for a month, and will still fire up like it had just been run.

Then you dont have a dead cell. Have the battery load tested before you replace it. Is the pulley on the new alternator the factory one, or one that came with the alternator. If it came with the alternator, is it the same size as the stock one.

I wouldnt mess with the fuel system voltage (can affect fueling), just the base voltage. Dont go over 13.8, or you will have other unwanted side effects.

[AlphaTuning]

I wouldnt mess with the fuel system voltage (can affect fueling), just the base voltage. Dont go over 13.8, or you will have other unwanted side effects.[/B]

Can you explain that a little more?

[HRD]

where did you source the smaller pulley? how many rpms were you turning?

Don't recall the actual numbers, but it was an aftermarked alternator from Street and Performance. Pulley fixed the problem.