chassis voltage issue?

[biscayne]

Brand new batteries, both 1050 CA. When I start the truck in the morning, it fires right up, volt meter looks fine. After idling in my driveway for a few seconds and pulling out of driveway, the dash lights get brighter and the headlights shine brighter. The change to brighter is definitely noticable, but the needle on the voltmeter isn't really moving and the engine rpm is well below 1000 rpm when the voltage apparently jumps up and stays up. i have not been able to catch it on a meter but am wondering if this is just the alternator "warming up" and other people's trucks do this or if this is the first sign from my alternator that I may need to plan a replacement.

[timmyboy76]

cheap insurance...

12 Volt Battery/Alternator Tester

[NoRalPh]

You should be able to get accurate voltage readings with a meter, from the in-cab "outlet", and monitor what's going on with the charging system. I sounds like you could have an alternator issue...

BUT, you're actually on to something with the "warming-up" you've noticed. What happens is, to protect the Alt from working too hard while the Glow Plugs are on, the PCM doesn't allow the Alt to start charging until it has cycled off the GPs. So, what you're seeing in the driveway might be pretty normal.

Keep an eye on the voltage, your regulator may either be fluctuating too much or actually be responding to a load that the Alt is having trouble dealing with or even a simple connection that's failing.

[Macon]

Throw the meter on the batteries before you start it. Record reading. Start the truck and then monitor the meter as it "warms up". See if there is any voltage spikes/changes/whatnot. My truck operates idles at 14.2VDC, off voltage is 12.3VDC.

[Turbostang500]

I'm with NoRalPh, the pcm is turning on the charging circuit in the alt after it shuts off the GP circuit. Mine does the same exact thing. I can even hear my fuel pump change tone.

[Matthews]

Has anyone ever checked the output of the alternator right after start up? I am pretty sure that the alternator puts out as soon as the truck is started. Given that the glow plugs are pulling from the power wire off the alternator between the alternator and the battery it is feasible that the voltage at the battery is still pulled down but if you clamped a current meter on at the alternator output I think you would see that the alternator is putting out. It's possible that the system voltage still comes up after the glow plugs turn off but I am betting its always putting out. If I get a chance in the near future I will double check it on my truck.

[timmyboy76]

Originally Posted by Matthews

It's possible that the system voltage still comes up after the glow plugs turn off but I am betting its always putting out. If I get a chance in the near future I will double check it on my truck.

According to my GPR-LED and VOltmeter, the second the led goes out, the voltage raises to 14-ish v. And if i fire truck up, prior to led going out, it stays lit til the gpr had done its cycle, then when it goes off, the volts raises to the 14-ish.

[Matthews]

The glow plugs probably pull the voltage down a little. If you see 14 volts on your volt meter when the truck is off you may as well ignore it all together because the voltage won't be 14. You can't go by the dash volt meter.

Voltage really isn't critical here. I am just saying tht I believe the alternator starts putting out current as soon as the truck is running. Wire sizing and loads all of can affect what your volt meter is reading at different times.

[Macon]

Voltage is critical, as he's experiencing voltage fluctuation. However, if the fluctuation is normal, then it's all good. The alternator likely isn't working while the GP's are on, as stated above. It would put maximum load on the alternator, followed by a sudden release. That's not good on alternators. That's not to say the alternator isn't producing electricity, it's just saying that the computer is fooling it into thinking there's no load, so it doesn't have to try so hard.

[NoRalPh]

Originally Posted by Matthews

The glow plugs probably pull the voltage down a little. If you see 14 volts on your volt meter when the truck is off you may as well ignore it all together because the voltage won't be 14. You can't go by the dash volt meter.

Voltage really isn't critical here. I am just saying tht I believe the alternator starts putting out current as soon as the truck is running. Wire sizing and loads all of can affect what your volt meter is reading at different times.

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