Pre-Power Stroke Diesel (7.3L IDI & 6.9L) Diesel Topics Only

7.3 Glow Plug Behavior

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Old 04-02-2016, 09:39 AM
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7.3 Glow Plug Behavior

I have a 92 F350 4X4 7.3 that is relatively new to me. Since I purchased it, the wait to start light has never worked and I'm not even sure if it normally appears on the left or right side of the gauge cluster. Where should I see the wait light?

When the key is turned on the glow plug relay clicks and you can see the voltage gauge move in unison with the clicking. when the clicking stops, turn the key and it always fires right up. The duration of the clicking cycle is shorter when the engine is warm and can be as few as 2 clicks or when cold as many as 8.

After reading the various threads related to glow plugs it would seem by that behavior many of the glow plugs are bad. So that correct? If so, I'll likely just replace them all.

One additional question, while replacing the injector return line system I got a little puddle of fuel down around one of my glow plugs. I could see bubbling from air around the glow plug. The glow plug didn't seem loose but I removed and reinstalled it nice and tight, that seemed to fix the problem. My question is, what if anything can you do in addition to snugging them down to prevent leakage around the glow plugs?

Thanks for any input you guys may have!
 
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Old 04-02-2016, 05:49 PM
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I always use lots of never seize on glow plugs, that'll help seal alittle, you could always try teflon paste, maybe even teflon tape to snug them up a little in the hole.

Here's a video of me starting my truck in 10F, when its really cold my WTS light doesnt come on, you can see the battery voltage drop and stay down until the plugs heat up then it starts cycling. If its cyling soon a glow plug is bad, or unhooked, or your harness is damaged

 
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Old 04-03-2016, 04:50 AM
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i would not use teflon tape or sealer on glow plugs, that could make them loose ground connection.
the "clicking" you hear is the controller going through it's after burn cycle.
i always hook a small light or now use a 12 volt LED hooked up to the output terminal of the glow plug relay.
this way i know for sure if the glow plugs are getting power or not.
you could have bad glow plugs, or more possibly you just have a bad wait to start light in the dash.
 
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Old 04-03-2016, 07:50 AM
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Thanks for the comments.. I'll test the glow plugs and the wiring harness and then see if I can fix the wait light.

I never have a problem starting the truck so it would seem that at least some of the glow plugs are working as they should.
 
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Old 04-03-2016, 08:10 AM
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it is very probable there is nothing wrong with the glow plugs if it starts cold without plugging it in.
even at 60-70 degrees, it will be hard to start without working glow plugs.
 
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Old 04-08-2016, 03:24 PM
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I actually checked my glow plugs today for leaks and found 4 of them leaking. I didn't initially torque them but was very careful on install. I put them in about 10,000 miles ago. I put a torque wrench on them this time, the ones i could reach at 12ft lbs and then got a feel for that with the 1/4 ratchet and tightened the rest. I got atleast 3/4 turn on all 8 of them. I had never seized them on install. The truck was hot after 70 miles of driving so I know it wasn't anything bubbling out from start up. This fixed all bubbling though. I wonder if it will effect fuel ecconomy at all? Truck starts fine even down to 10f.
 
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Old 04-08-2016, 08:13 PM
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Considering the volume of air going through these engines(and the leakage past the rings), a tiny amount going through the threads isn't going to make a bit of difference.
 
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