1990 HDJ81 glow plug voltage

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CountFloyd

CountFloyd

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Good day,
Troubleshooting the glow plug circuit in my truck. And I only have 7.5 volts being delivered to the glow plugs.
I have unfortunately misplaced my FSM.
But part of me is assuming I should be getting 12 volts.
Is that correct?
And would the likely culprit of the voltage drop be the glow plug relay?
Anyone have any idea where it would be located?
Thanks.
 
ceylonfj40nut

ceylonfj40nut

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Is your truck 12v or 24v?
 
ceylonfj40nut

ceylonfj40nut

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I think @bj40green may have addressed glow plugs and voltage. I am aware glo plugs have different voltages. Might want to share what you have installed.
 
CountFloyd

CountFloyd

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I would have to check with the supplier I bought them from. I replaced them when I did the head gasket last year.
I trust both the parts guys and mechanic not to install the wrong parts.
Just seems weird to me that it would be 7.5 volts to the glow plugs.
 
Squash

Squash

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# 19850-64031
1990 till at least 1997.
You can also try a cross -reference check of the part number for other suppliers.
My HZJ75 & hdj81 both have these plugs.
# 19850-17020 looks like it also works from 1990 to current in the HZJ79 series.
Our Hdj and Hzj engines share many parts....
 
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Squash

Squash

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I would have to check with the supplier I bought them from. I replaced them when I did the head gasket last year.
I trust both the parts guys and mechanic not to install the wrong parts.
Just seems weird to me that it would be 7.5 volts to the glow plugs.
Your plugs will start hot and then cool down. Maybe you caught them on the down cycle.
 
CountFloyd

CountFloyd

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Checked again this morning.
The glow light only flashes for about a 1/4 second.
The voltage drops immediately after the light goes out. Doesn’t engage long enough to know what it is, but drops to 6.5 volts to ground.
Swapped a spare timer relay, same thing…
 

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