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'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #1 of 4 (permalink) Old 11-30-2012, 10:54 PM Thread Starter
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glow plugs!

Having a bit of a starting issue. Hard start and white smoke. Kind of hard to get a handle on as temps have been up and down, just trying to get some ideas of things to look at. I have new batteries and a new gpr. How many amps will will the glow plugs pull when cycled on? Do they pull more the colder the temp is? I searched the form but all I found were ohm readings for the glow plugs themselves.

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post #2 of 4 (permalink) Old 11-30-2012, 11:27 PM
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Should be somewhere between 100-200 amps or more depending on actual resistance of the individual plug. ohms x voltage=current

They don't draw more current if it is colder, they just stay on longer at their normal draw.

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post #3 of 4 (permalink) Old 12-01-2012, 03:36 AM
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Spec for GPs are .3 to .5 ohms. Since there are 8 in parallel, that's .037 to .0625 ohms. Using this range of resistance and ohms law to solve for current (i=e/r) assuming 12 volts, that's 12V/.037Ohms=324 Amps to 12V/.0625Ohms=192 Amps. To calculate the power in watts use (p=i*e), or 3888W to 2304W. In theory, the hotter the GP gets the higher its resistance becomes (less current draw). The difference in initial current draw between a 70F and -20F GP is minor when you consider an energized GP reaches about 2000F. Normally when GPs fail their resistance increases, so anything above .5 ohms is considered bad.

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post #4 of 4 (permalink) Old 12-01-2012, 11:27 AM
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Factory specs for a good ZD-11 glow plug from the Ford manual is 0.6-2 ohms for a good glow plug.

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