Glow Plug Relay Voltage

[hrbergeron]

I believe there is a problem with my glow plug system. When starting, it takes around two revolutions of the engine before the engine starts. Is this normal?

I assume it should act like my HMMWVs and start on the first revolution. Then again, my Ram 2500 takes around two revolutions to start with the glow plugs.

Using the TM 9-2320-289-20 for the glow plug system diagnosis, I get 10.8v at the orange wire. The TM says, "if there are 10.0-15.0 volts, ensure that engine is mechanically sound and fuel system is operating properly." The diagnosis chart is for the engine cranking and not starting, but mine starts, so the flow chart stops there.

The glow plugs are brand new. The wait light comes on for a "normal" time. The resistor pack is bypassed. I suspect it is the glow plug card. I had to solder some connections back on where they had cracked the original solder and were loose. I suspect it is the glow plug card because I would assume that the glow plugs should be receiving close 12v, not 10.8v.

 

[Russm]

I just replaced mine and they all had "10.5v" stamped on them.
But I haven't had to mess with the glow plug system yet so I am no expert.

I can add that with rebuilt starter, new batteries and warm outside the fastest its ever started was after 2 cha-cha's

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[Barrman]

The -20 manual has a wonderful 76 page long troubleshooting section. Then another trouble shooting section on just electrical stuff. The opening page of that section states in very clear terms to make sure you have two batteries that are fully charged and have been load tested before doing any electrical diagnostic work.

Do you have a pair of fully charged batteries that have been load tested? That has to be done first.

I will add this. When I got my 1st M1009 it would take a few seconds of turning before it started. I thought it was normal. A few months later it wouldn't start at all one morning. I tried and tried and it finally started but something was wrong. The next time I tried starting it the engine just barely spun over. I slaved it to a M35 and it still barely spun over. I crawled underneath and the starter motor was almost too hot to touch after just a few seconds of use.

2 new batteries and a rebuilt starter later the truck would start before I could think to let off the key. It has continued that for the past 9 years. Did I have a bad starter that killed the batteries or a bad battery killed the starter with an under volt issue? Get your batteries checked and fully charged. Then proceed.

 

[hrbergeron]

Batteries are charged and less than a month old. Has a new starter I installed two months ago, haven't driven it further than around the block while I'm restoring it. Still 24v and staying that way.

 

[hrbergeron]

Perhaps voltage supplied affects overall temperature? For example, today the ambient air temperature was around 80 degrees Fahrenheit. If a glow plug is supplied with 14v instead of 10v, it will get more hot. I'm curious if the voltage would increase based on the temperature of the engine and the glow plug card calculating on that. This is only an idea, I'd have to check voltage again when it gets cold outside.

 

[MarcusOReallyus]

Perhaps voltage supplied affects overall temperature? For example, today the ambient air temperature was around 80 degrees Fahrenheit. If a glow plug is supplied with 14v instead of 10v, it will get more hot. I'm curious if the voltage would increase based on the temperature of the engine and the glow plug card calculating on that. This is only an idea, I'd have to check voltage again when it gets cold outside.

Nope. The GPs either get battery voltage or nothing. No graduated voltages.

There is a temperature sensing function, but that only helps the GP controller to decide whether to turn on or not, and for how long. There is no provision to vary the voltage applied to the GPs.

When are you are getting 10.8 at the orange wire? Is that while the GPs are energized?

 

[hrbergeron]

Nope. The GPs either get battery voltage or nothing. No graduated voltages.

There is a temperature sensing function, but that only helps the GP controller to decide whether to turn on or not, and for how long. There is no provision to vary the voltage applied to the GPs.

When are you are getting 10.8 at the orange wire? Is that while the GPs are energized?

Yes, getting 10.8 while they ate energized, both at the glow plug and orange wire.

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[antennaclimber]

Check the voltage drop across the GP relay.

Then work your way back to the batteries to see if there is a place where the voltage begins to sag.