Voltage drop on GPR - Diesel Forum - TheDieselStop.com
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Old 02-08-2009, 04:15 PM Thread Starter
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Voltage drop on GPR

The voltage on my GPR drops 2 volts when the key is on. Is this normal? I have been having some cold starting issues. I read somewhere that .5 volt drop was typical.
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Old 02-08-2009, 04:38 PM
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Yeah, 2 volts is a bit excessive. If it's dropping two volts, and passing about 150amps, then it's dumping about 300W of heat in there, and it probably won't last much longer.

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Old 02-08-2009, 04:43 PM
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I think you might be confused.
The 2 volt drop you see should be how much the batts drop when you turn key on. I say this because when glow plugs are off you will see about 12.5 volts and when turn key on with glow plugs heating the bat volts drops about 2 volts. Now the drop of .5 volts should be max difference when you check each large post on GPR while GPR is activated and G Plugs are drawing


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Old 02-08-2009, 04:56 PM
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I think you're right, Excavator - most likely a 2v drop in the dash gauge when the glow plugs are active, not a loss of 2v across the glow plug relay.

How 'bout it Jawmaw? Is the dash gauge what you are looking at or are you checking voltage on the two big terminals on the glow plug relay?

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Old 02-08-2009, 05:17 PM
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Quote:
Originally Posted by jawmaw View Post
The voltage on my GPR drops 2 volts when the key is on. Is this normal? I have been having some cold starting issues. I read somewhere that .5 volt drop was typical.
Better idea: Check the glow plug amperage to make sure your GP system is working correctly. Amperage should be 195 initially, tapering off to 125 after 30 seconds. An inductive clamp around the battery cable leading to the glow plug relay will do. You can test each side by putting your inductive clamp on each feed off of the relay, good results are about 90 amps initially.


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Old 02-09-2009, 12:28 PM
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.5 volts is even a little much, .1 volt

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Old 02-09-2009, 01:22 PM
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Originally Posted by jawmaw View Post
The voltage on my GPR drops 2 volts when the key is on. Is this normal? I have been having some cold starting issues. I read somewhere that .5 volt drop was typical.
Where are you seeing the 2 volt down at? Are you talking about a 2 volt drop between the two big posts on the glow plug relay? Or a 2 volt drop in battery voltage? If it is a 2 volt drop across the relay posts then your GP relay is bad. If it is a 2 volt drop in battery voltage I think one or both of your batteries are weak or your battery cables to the relay are bad. Just my 2 cents.

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Old 02-09-2009, 01:53 PM
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if he is seeing 12.5 batt volts with key off and sees 10.5 batt volts with key on and g plugs activated then that is good.

I am not sure when or where he is taking reading


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Old 02-09-2009, 05:33 PM Thread Starter
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I am taking the reading across the 2 big terminals on the GPR. Thanks for the replies. I will be replacing the GPR soon.
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Old 02-09-2009, 07:21 PM
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If you're dropping 2v across the terminals, replace soon as possible. With that drop it should be smoking by now.

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Old 02-09-2009, 09:43 PM
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I stand corrected. Biggest drop I have seen so far for a functioning relay.

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