relay cycling on and off

[Kenneth Cole]

Good day
I have a 1991 with a 6.2. Recently after starting her up and for several minutes it sounds like a relay is cycling on and off in the area of the starter switch. As it does the volt gauge drops and then goes up somewhat as the relay cycles off. Eventually it stops cycling and the volt gauge goes up to normal. I am not that knowledgeable on the diesel engine so let me know if I am thinking right that this is the glow plugs cycling on and off and what should I do to correct this.

Thanks for the help.
Ken

Marry Christmas to all.

 

[Carrera911]

It’s the PCB box under the dash telling the glow plugs to cycle on and off. It’s like that by design but I’m not sure why it does it. No other diesel I’ve been around has this “feature”. It just seems to waste more life of the glow plugs imo.


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[TOBASH]

IIRC, some of the PCB units continue to fire the glow plugs until engine is operating at optimum temps.

This can cause flickering of some lights while glow plugs cycle, and some other phenomenon.

From what I have read, it is within normal operational parameters for the vehicle to do these things.

Behind the dash, on the left, under the area where the ignition switch sits, you can look underneath and see the PCB/ Protective Control Box. Take a picture of the label and post to ID the specific PCB you're vehicle is using. You can also listen to that area or place and automotive stethoscope on that device to listen when you start the vehicle to confirm the reply by Carrera911.

Best,

T

 

[90Jimmy]

Good day
I have a 1991 with a 6.2. Recently after starting her up and for several minutes it sounds like a relay is cycling on and off in the area of the starter switch. As it does the volt gauge drops and then goes up somewhat as the relay cycles off. Eventually it stops cycling and the volt gauge goes up to normal. I am not that knowledgeable on the diesel engine so let me know if I am thinking right that this is the glow plugs cycling on and off and what should I do to correct this.

Thanks for the help.
Ken

Marry Christmas to all.

My 998 does the exact thing you are describing when it's colder than normal around here, like below freezing....I also have 2 CUCV M1009's and they do the same thing when its cold. Now, no more worries until the next worry.... HMMWV's are FUN!!

 

[Retiredwarhorses]

This is called “after glow” it’s an emissions thing....this annoying feature is gone in the newest S3 box...well, not gone per say, just done in a different manner then the 2mins of Zapping the GP’s with 24 volts.

 

[papakb]

The earliest series of Prestolite control boxes used starter solenoids to switch the current out to the glow plugs and that's the "cluck" you hear when you turn on the ignition. That cycling keeps going until the glow plug control on the crossover manifold tells the PCB that the engine is over 120 degrees. As Steve says, this is referred to as "afterglow". The newer control boxes changed their current control devices to solid state stuff that doesn't make any sound as it switches on and off but you will still see the voltmeter dip as they cycle.

When the Marines would have problems with these early boxes they'd give it a swift kick with their left boot to encourage it to work! LOL