M1152 400 Amp alternator voltage jumping.

[Mattguy]

On my 2006 M1152 after starting for the first time, the voltage will surge up and down, but after about a minute it will stabilize. Could the voltage regulator be going bad possibly? Batterys are fully charged.

 

[Coonass77]

It's your start box pulsing the glow plugs. Completely normal.

 

[Backdraft]

On my 2006 M1152 after starting for the first time, the voltage will surge up and down, but after about a minute it will stabilize. Could the voltage regulator be going bad possibly? Batterys are fully charged.

Most likely what you are seeing is the glow plug controller cycling the plugs. That’s normal operation on a cold start.

 

[Mattguy]

Most likely what you are seeing is the glow plug controller cycling the plugs. That’s normal operation on a cold start.

My M1123 never does that on cold start. Is that something different with the turbo trucks? It does it for about 45 seconds after starting.

 

[Mullaney]

My M1123 never does that on cold start. Is that something different with the turbo trucks? It does it for about 45 seconds after starting.

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+ Edits

No this is standard SOP for all these trucks with the standard PCB Box on it. The glow plugs turn on, turn the "wait light" off, then you crank the truck. Then the glow plug controller to "pulse" the voltage to the glow plugs to help warm up the cylinders more quickly.

The pulsing is called "After Glow".
(Thanks for the term @Mogman !)

 

[Backdraft]

My M1123 never does that on cold start. Is that something different with the turbo trucks? It does it for about 45 seconds after starting.

That’s exactly what my 998 does. I’ve never been in one that didn’t cycle the plugs like that unless the engine is warm.

 

[Coonass77]

My M1123 never does that on cold start. Is that something different with the turbo trucks? It does it for about 45 seconds after starting.

My m1123 with the 200a alternator and older style start box didn't do it either, but my M1165 with the 400a and older style start box does.

 

[Mogman]

It's called "afterglow"
As I understand some boxes reduce the voltage to the glow plugs for afterglow and others pulse the plugs on and off.

 

[Mattguy]

My m1123 with the 200a alternator and older style start box didn't do it either, but my M1165 with the 400a and older style start box does.

Must be two different control boxes. My M1152 with 400amp alternator is massive. Can't even get to fuel filter.

 

[Mogman]

The box we are talking about is the EESS box in the space above the pedals, would not be dependent of alt, but would explain why some see the pulsing on the volt meter and some do not, the boxes that reduce the voltage to the glow plugs would not cause the volt meter to move back and forth.
JUST another reason to have a dash lamp attached to one of the glow plug wires, so you have some idea WHAT is ACTUALLY going on with the glow plugs

 

[Retiredwarhorses]

This has been covered a hundred thousand times…but here goes.
All boxes prior to S3 EESS pulse 24v for 2mins after start up, upon the introduction of the S3 EESS, it is now a constant
5 vdc for 2min, not observable on the voltage gauge.

 

[GTUnit]

The voltage surges where? Measured where?

 

[Mogman]

The voltage surges where? Measured where?

You can see the volt meter needle swinging back and forth after startup for a minuet or two.

 

[Mogman]

This has been covered a hundred thousand times…but here goes.
All boxes prior to S3 EESS pulse 24v for 2mins after start up, upon the introduction of the S3 EESS, it is now a constant
5 vdc for 2min, not observable on the voltage gauge.

And we will continue EVEN if we had a well thought out, simple "NEWBIE READ THIS FIRST" Sticky but it sure could not hurt.

 

[Maxjeep1]

My m1123 with the 200a alternator and older style start box didn't do it either, but my M1165 with the 400a and older style start box does.

My M1123 does it. 2002 year model

 

[SmartDrug]

My M1123 does it. 2002 year model

My 1999 does it as well. I use it as my baseline amount of time to warm up before I drive it.

 

[Maxjeep1]

I don’t know sometimes I think we look for problems.. if it starts in the first 5 seconds and it goes in gear we are looking good! I was driving my truck today and I was thinking is it idling a little high and then I thought I felt a small vibration. I have never worried so much about a vehicle and I usually jump in and drive the piss out of them.

 

[Retiredwarhorses]

Model year of your truck means Absolutely nothing as the model year doesn’t mean you have an S3 EESS installed.
older trucks have old PCB’s and yellow label KDS and Nartron boxes….99% of M1123’s have Yellow Nartron EESS.
newer turbo trucks have been consistently running S3, as they should.

 

[SmartDrug]

Model year of your truck means Absolutely nothing as the model year doesn’t mean you have an S3 EESS installed.
older trucks have old PCB’s and yellow label KDS and Nartron boxes….99% of M1123’s have Yellow Nartron EESS.
newer turbo trucks have been consistently running S3, as they should.

Yellow EESS here - I figure the year/serial would be somewhat relevant for the USMC trucks that were subject to IROAN, as they wouldn't have replaced those components unless something failed, right? I do understand your point here, though. Like any HMMWV, or any .gov vehicle, it's going to be a tossup as far as pretty much everything.

 

[Retiredwarhorses]

Yellow EESS here - I figure the year/serial would be somewhat relevant for the USMC trucks that were subject to IROAN, as they wouldn't have replaced those components unless something failed, right? I do understand your point here, though. Like any HMMWV, or any .gov vehicle, it's going to be a tossup as far as pretty much everything.

my point was people posting model year as if that had a bearing on what PCB,EESS or Smart start they might have in the truck, even your “yellow label” does say which Mfg you have,
Your observations are based on ? One truck you own or owned? Mine are based on trucks arriving every day into the shop for the last 10yrs, mine is not a 10k foot view.