Odd charging problem

A few days ago it was warm enough out that when I went to start my HMMWV the wait light didn't come on. I waited about 60 seconds and then started the engine The voltage gauge went into the yellow and stayed there. Usually it bounces between yellow and green for 60-90 seconds as the system runs the glow plug heating cycle and then goes into the green and stays there. The digital voltage gauge I have usually reads 28v, this time it said 24.3 volts, definitely not enough to charge the batteries.

I started the truck later to come home (again, too hot for the wait light, but waited 60 seconds) and the meter did it's usual bounce and then went to green. The digital gauge read 28v as expected.

Just to see what would happen, that evening I started it again (again, too hot for the wait light, but waited 60 seconds) and it didn't bounce and stayed in the yellow. And the digital gauge was back at 24.3v.

Anyone have any idea about what's going on, and how to prevent the system from not charging if the glow light doesn't come on?

I should mention that I looked through the TMs and didn't see this exact set of symptoms.

My opinion is that the glow plug functioning has nothing to do with whether the alternator charges or not. Look at the alternator for issues or lack of power to the alternator excite wire.

Are you leaving it in RUN for 60 seconds before starting? Or, starting then waiting 60 seconds to view the voltmeter?

And, why do folks always say that is is warm enough outside to not need the glow plugs to come on?

Action said:

Are you leaving it in RUN for 60 seconds before starting? Or, starting then waiting 60 seconds to view the voltmeter?

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I'm leaving it on RUN for 60 seconds before starting.

Action said:

And, why do folks always say that is is warm enough outside to not need the glow plugs to come on?

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It's not that the glow plugs don't need to come on for the vehicle to run, it's that they system doesn't need to preheat them. So the wait light never comes on. My assumption is that the control box "knows" that the engine is already warm enough to not need to cycle them for heating, so it doesn't and it doesn't light the wait light.

NDT said:

My opinion is that the glow plug functioning has nothing to do with whether the alternator charges or not. Look at the alternator for issues or lack of power to the alternator excite wire.

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That's possible, but it's only ever happened when the wait light didn't come on. If the wait light comes on, I always get the voltmeter bounce after starting and when the preheating cycle is over it goes to green. I'm hoping it's not a sign that my control box is going...

riderdan said:

I'm leaving it on RUN for 60 seconds before starting.


It's not that the glow plugs don't need to come on for the vehicle to run, it's that they system doesn't need to preheat them. So the wait light never comes on. My assumption is that the control box "knows" that the engine is already warm enough to not need to cycle them for heating, so it doesn't and it doesn't light the wait light.

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If the wait light doesn't come on in the RUN spot, you can immediately turn to START.

I lived in IN, then SW FL. I have always had my WAIT light come on when the engine is cold. Ambient temp near 100, and my WAIT light still comes on.

If I recall correctly, you've had your ride a while and have done the usual recommended improvements like a grounding harness and all that? Were it me, I'd check all connections first, particularly all the ground wires and the alternator wires connections as noted.

If it still acts odd, I recommend twiddling the regulator. My HMMWV did this kind of thing right before the regulator burned up. I haven't made the time to dig into the potted electronics of the old regulator, which I saved bc it looked fine visually, to see if my theory that the adjusting potentiometer was fouled with carbon dust from the brushes, but I will.

My money is on loose connections. You could just tighten them, or remove, wire brush and retighten, up to you and your time schedule.

Bulldogger

Bulldogger said:

If I recall correctly, you've had your ride a while and have done the usual recommended improvements like a grounding harness and all that? Were it me, I'd check all connections first, particularly all the ground wires and the alternator wires connections as noted.
If it still acts odd, I recommend twiddling the regulator. My HMMWV did this kind of thing right before the regulator burned up. I haven't made the time to dig into the potted electronics of the old regulator, which I saved bc it looked fine visually, to see if my theory that the adjusting potentiometer was fouled with carbon dust from the brushes, but I will.
My money is on loose connections. You could just tighten them, or remove, wire brush and retighten, up to you and your time schedule.
Bulldogger

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Good advice. I'll dig into that next

Your generator is not charging, easiest test is check voltage at batteries before start and then after, before start will be battery voltage, after start 27.5-28.5volts.
A bad EESS will prevent your batteries from charging, assuming you have a 60amp generator, if a 200amp, then that’s a different TS path.
Let’s be clear about glow plugs and engine temps...makes no difference on “OAT” outside air temp, it’s what the TSU sends to the EESS that matters, unless the engine temp is 120 or greater, it will fire the plugs.