Glow Plugs not firing? - Diesel Forum - TheDieselStop.com
7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

 
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post #1 of 8 (permalink) Old 11-21-2018, 04:59 PM Thread Starter
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Glow Plugs not firing?

Hey I just bought this '94 7.3 IDI Turbo Diesel a month ago. It wouldn't cold start apparently on account of a few of the glow plug connectors being broken and not hooked up. There is a heating block on it so I have been using that to start the engine in cold weather, and after 20 minutes of being plugged in it starts right up. Finally got around to changing the connecters, and I went ahead and changed all the glow plugs as well. It started up, but the ambient temp wasn't very cold. Later that night I tried again and it wouldn't start. Tested the relay with a multimeter and it wasn't putting anything out so I bought a new relay and replaced it.

Still won't start unless I plug in the engine block, or unless its warm outside. Before I replaced the relay the wts light would stay lit for about 3-4 seconds then turn off. Ever since I have put a working relay in, the wts light comes on for maybe half a second then turns off, then the relay clicks. It will start in warm temperature, but not cold unless plugged in. I'm not sure what to look for now. I've read about a coolant temp sensor. Is that the culprit? If so, where is it? I cant find anywhere on the internet that shows me where it is, unless im staring right at it but think its something else.

Thanks ahead of time for any help
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post #2 of 8 (permalink) Old 11-21-2018, 06:24 PM
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You need to check and see if the controller is sending juice to the glow plugs, Test light out under the hood either at a glow plug or right at the controller.
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post #3 of 8 (permalink) Old 11-22-2018, 10:34 AM
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That symptom is also an indication of some open or shorted glow plugs. After sitting oernight check with an ohm meter (glow plug to ground). The reading should be around .2 ohms.

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post #4 of 8 (permalink) Old 11-22-2018, 03:38 PM
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As suggested above, I would re-test the glow plugs with an ohm meter and also test the GPR with a voltmeter.

Are you blowing out any white exhaust when cold starting?

BTW, did you use Motorcraft brand ?

Its also possible you have a different issue that functions “just enough” with a warm engine but I would rule out the GP system 100% before looking elsewhere.


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post #5 of 8 (permalink) Old 11-22-2018, 09:16 PM
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WTS light should be on for 11-14 seconds. As asked what brand of plugs did you use. If you used Autolite, throw them in the trash and consider it a lesson learned. Motorcraft or Wellman only.

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post #6 of 8 (permalink) Old 01-31-2019, 10:52 AM Thread Starter
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Hey y'all thanks for answering. Sorry had to abandon this post as some unfortunate events happened and I had to tend to them. I figured out the problem though and it was pretty simple. The relay wasn't getting the full 12 volts so I followed the wire back to the battery and found a splice in the middle of the wire that wasn't connected as good as I wanted it to. Repaired it and the engine started right up
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post #7 of 8 (permalink) Old 01-31-2019, 10:52 AM Thread Starter
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Oh yeah. I did use motorcraft
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post #8 of 8 (permalink) Old 01-31-2019, 02:36 PM
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Quote:
Originally Posted by koots55 View Post
Hey y'all thanks for answering. Sorry had to abandon this post as some unfortunate events happened and I had to tend to them. I figured out the problem though and it was pretty simple. The relay wasn't getting the full 12 volts so I followed the wire back to the battery and found a splice in the middle of the wire that wasn't connected as good as I wanted it to. Repaired it and the engine started right up
Nice job !


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