Volt meter surges at start up

[Lazboytt]

Hello,
Not sure if this topic was already covered as I could not find anything specific.

When I start my 93 M998 the volt meter surges from normal to low and so forth. After a few minutes or so it stays at normal. I believe the headlights also dim down when this happens but I would have to re verify.
Any ideas?
Someone said something about this happens when the glow plugs run but not sure if this is accurate or not.

 

[1 Patriot-of-many]

Every box except the S3 smart start box has after glow(keeps cycling the glow plugs on and off for a few moments resulting in the voltmeter moving) for the glow plugs. Which box is in your vehicle?

 

[Lazboytt]

Hello,
That I do not know. Where would I find that I can look after I get off work today

 

[papakb]

When you get pissed because the truck is being a PITA and you thrash out and kick the firewall with your left foot you'll find the control box, in fact, that was an old Marine Corps fix for trucks that didn't want to start! It's mounted beneath the deck where the windshield washer tank is. There are usually labels of various colors on them that show the manufacturer of your particular unit. If it's just a black box chances are it's made by Prestolite.

The control box takes inputs from the glow plug controller and turns on the glow plugs when it senses the engine is cold and turns them on in a 10-12 second cycle. This continues after the engine starts until the temp sensor sees the engine starting to warm up. This is called afterglow and is completely normal and can last for a minute or two if it's really cold. You should see the voltmeter dip indicating that current is flowing to the glow plugs, if you don't then you may have burned out glow plugs. You can check them with a simple multimeter on the resistance scales. With the Prestolite boxes the glow plug current is switched with a relay contactor accompanied by a healthy "clunk". With later control boxes with semiconductor devices you won't hear that cluck.

 

[Bulldogger]

The 1-2 minute cycling is normal startup procedure. If it happens when the engine is hot, or lasts longer than 2m, only then is there an issue.
Most refer to this as Afterglow

Bulldogger

 

[Lazboytt]

Thank you for the help. Glad to know this is normal as I just picked mine up and was worried something might be wrong with the unit.

Thank you everyone for your replies.