Glow Plug Resistance
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Laughing Gas
Joined: Aug 2003
Posts: 836
Likes: 9
Glow Plug Resistance
Doing a little research on what normal resistance is for a 7.3 glow plug and I am getting conflicted findings. On the forum I read that anything under 2 ohms is good. On sites like this one it says that they should read under 1 ohms with most good glow plugs read between .01 and .05 ohms ????
7.3L IDI Glow Plug Troubleshooting
7.3L IDI Glow Plug Troubleshooting
Fleet Mechanic
Joined: Aug 2006
Posts: 1,465
Likes: 17
From: Jacksonville, FL
Originally Posted by 1L243
Doing a little research on what normal resistance is for a 7.3 glow plug and I am getting conflicted findings. On the forum I read that anything under 2 ohms is good. On sites like this one it says that they should read under 1 ohms with most good glow plugs read between .01 and .05 ohms ????
7.3L IDI Glow Plug Troubleshooting
7.3L IDI Glow Plug Troubleshooting
Logistics Pro
Joined: Oct 2011
Posts: 3,953
Likes: 120
From: Mcdonough, GA
And where are you taking readings. If measuring directly at the tip of the plug it will be closer to the .5 but if your measuring through the harness it could be higher. the .5-2 mentioned above is what your looking for
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Laughing Gas
Joined: Aug 2003
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I test at the harness.
I tested my Glow Plugs about two years ago and found four all on one side completely open over the 200 on the ohm meter.. I also tested them when I removed them from the truck all four were bad. The other side was fine. I replaced all four. I am going to test them again and came across the discrepancy on what a proper ohm reading would be for a good Glow Plug. It's easy of the plug is off the chart but if they come in at 1.5 vs .05 is it bad?
I tested my Glow Plugs about two years ago and found four all on one side completely open over the 200 on the ohm meter.. I also tested them when I removed them from the truck all four were bad. The other side was fine. I replaced all four. I am going to test them again and came across the discrepancy on what a proper ohm reading would be for a good Glow Plug. It's easy of the plug is off the chart but if they come in at 1.5 vs .05 is it bad?
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Laughing Gas
Joined: Aug 2003
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So far tested the drivers side and all glow plugs are within specs at .03 to .05.. But testing seems fickle.. reading changes by a few points from one minute to the next. I assume the ground is critical, I am using the negative battery terminal, is this the best location for grounding the ohm meter?
Any problem with using dielectric grease when putting the connector back together?
Any problem with using dielectric grease when putting the connector back together?
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Logistics Pro
Joined: Oct 2011
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From: Mcdonough, GA
The engine block may be a better ground point for this test but it looks like they all came in good.
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Laughing Gas
Joined: Aug 2003
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Just checked passenger side and all is good between .02 and .03.... So, checked the Glow Plug Relay and Wala! no voltage on when turning on the key... So now I know why my truck (which I park in the garage) has been hard starting the last couple of months... So, off to get a new relay tomorrow....
Hotshot
Joined: Mar 2014
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From: Douglassville, PA
Are numbers like .02 and .03 typical? I checked mine and they were all like 1.5 and they are fairly new glow plugs. I also ohmed out a set on another engine and they came in at about 1.3 with consistent readings across all of them (except for one that was over the top). And I didn't see much difference whether I went right to the glow plug (I pulled one out and tested it) or if I went through the UVCH testing from the outside of the VC.
Logistics Pro
Joined: Oct 2011
Posts: 3,953
Likes: 120
From: Mcdonough, GA
Are numbers like .02 and .03 typical? I checked mine and they were all like 1.5 and they are fairly new glow plugs. I also ohmed out a set on another engine and they came in at about 1.3 with consistent readings across all of them (except for one that was over the top). And I didn't see much difference whether I went right to the glow plug (I pulled one out and tested it) or if I went through the UVCH testing from the outside of the VC.
every meter does not read the same. Some will have a little resistance in the leads. If you touch your leads together does it show 0 or .4 or .7?? Did you use digital or analog? IIRC mine were all around 1.0 through the harness. They were below 2 and all about even so I didn't think must past that.
Fleet Mechanic
Joined: Aug 2006
Posts: 1,465
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From: Jacksonville, FL
Originally Posted by AllaboutMPG
Walleye,
every meter does not read the same. Some will have a little resistance in the leads. If you touch your leads together does it show 0 or .4 or .7?? Did you use digital or analog? IIRC mine were all around 1.0 through the harness. They were below 2 and all about even so I didn't think must past that.
every meter does not read the same. Some will have a little resistance in the leads. If you touch your leads together does it show 0 or .4 or .7?? Did you use digital or analog? IIRC mine were all around 1.0 through the harness. They were below 2 and all about even so I didn't think must past that.