M998 VOLT GAUGE GOES LOW DURING KICKDOWN

[Iambiig]

gauge is usually in the green (a little past the little white reference line). During kickdown, the gauge goes to yellow for a few seconds, then goes almost to red, then back to normal. 200A dual voltage alternator with triple belts.

Is this ok, or is something about to break?

 

[Mogman]

What do you mean by "kickdown"?

 

[Coug]

How old are your batteries and have you had them tested?
I noticed a few issues with the voltage not staying steady when I had a bad battery once upon a time.

 

[NDT]

Are your batteries well restrained?

 

[Iambiig]

What do you mean by "kickdown"?

when you press the accelerator and the trans kicks to a lower gear in order to go faster.

 

[Mogman]

when you press the accelerator and the trans kicks to a lower gear in order to go faster.

That is an odd one!
Check all the connections on the reg and the ground to the alt.
I assume all the belts are in good shape and tight.

 

[Mogman]

Do you have any other electrical issues? Any other gauges not reading correctly or intermittent?
You may also want to clean the inst. panel ground, it is located behind the inst. panel, it is a bolt through the firewall that has wires attached both sides so you need to clean the connections inside the cab and inside the engine compartment.

 

[Iambiig]

How old are your batteries and have you had them tested?
I noticed a few issues with the voltage not staying steady when I had a bad battery once upon a time.

batteries are 2 years old and were supposed to be 2 year batteries. I rotated last year, starts fine. Belts look like they have some play. Was thinking they may be slipping when engine is revved. Can this happen?

 

[Iambiig]

Are your batteries well restrained?

very restrained!

 

[Coug]

batteries are 2 years old and were supposed to be 2 year batteries. I rotated last year, starts fine. Belts look like they have some play. Was thinking they may be slipping when engine is revved. Can this happen?

the 200 amp has a lot of mass, so belts could slip if loose. Your description of it only happening when the engine is revving up under heavy load though would make me suspect it doesn't have anything to do with the belts, as even if slipping the alternator shouldn't be dropping in speed when the engine kicks up like that.

Even if it starts fine, it doesn't mean the batteries are in as good of shape as they could be. At minimum use a multimeter on each of them after it sits for a day or two and see if there is any difference in voltage levels between them.

 

[Mogman]

The belts "look" like they have play? ether they are tight or not, this is of course checked with the engine not running and should have already been checked as part of normal maintenance, it is perfectly normal for the belts to "jump" up and down while running.
Yes they can slip but it seems doubtful it should put the volt meter in the red, even though the factory meters are notoriously inaccurate.
With the engine fully warmed up where you would have no glow plug activity what does the meter read when the run switch is turned to the run position but before starting?
If you have not already done so attach a volt meter to your batteries and see what is actually happening, At this point I would suspect a loose connection or a faulty ground.

 

[Coug]

When you're flooring the accelerator and the trans kicks down, the entire engine/transmission assembly does some twisting against it's mounts. The only thing I can think of is you have a bad wiring connection between the alternator and the batteries somewhere that is getting affected by this twisting.

Check over the wire connections at the alternator and the starter, and make sure the cables don't have any damage to them.

Make sure to check the ground strap from the alternator to the engine block as well. I know on my truck it was very loose when I first got it.

 

[Coug]

Another thought, did it come from the military with the 200 amp alternator installed, or was it done afterwards? The 200 amp uses larger cables than the 60 amp, and they should be routed over to the starter solenoid if I remember correctly, whereas the 60 amp wire went to the control box and through a solenoid before going to the batteries. If it was installed incorrectly that could also cause some electrical issues for you.

Since you have it, you also might as well get some 8 gauge cable to wire from the voltage regulator to the rear battery, and never have to worry about rotating the batteries again.

 

[Mogman]

Post a pic of the top of the engine/alt

 

[Iambiig]

When you're flooring the accelerator and the trans kicks down, the entire engine/transmission assembly does some twisting against it's mounts. The only thing I can think of is you have a bad wiring connection between the alternator and the batteries somewhere that is getting affected by this twisting.

Check over the wire connections at the alternator and the starter, and make sure the cables don't have any damage to them.

Make sure to check the ground strap from the alternator to the engine block as well. I know on my truck it was very loose when I first got it.

Thank you, will do

 

[Mogman]

Also what model truck?

 

[Iambiig]

Post a pic of the top of the engine/alt

 

[Mogman]

It has the correct wiring for a 200A