SOLVED! The same glow plug constantly roasting mystery..

[Humpty]

SOLVED!

Updating for the benefit if anyone else who may encounter this or a similar issue. What ended up being the culprit was injector lines 5 and 6 were reversed at the injector pump.

Firing order being 1,8,7,2,6,5,4,3 essentially cylinder 6’s fuel was getting blasted onto 5 prematurely.. collecting on the glow plug and eventually burning off, roasting the glow plug.. even with the glow plug completely disconnected from the glowplug controller.

I’d been told that by the previous owner that the pump had been “rebuilt” but then the truck had sat for a couple years afterward. I didn’t think to check the lines just because I assumed since they were custom bent that you couldn’t hook them up wrong. Evidently you can.

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M998A1 with 6.2, i’ve now replaced 4 glow plugs on the same cylinder.

A popular theory was that the injector was leaking and dripping fuel onto the glow plug. The normal heating cycle of the glow plug was igniting the glow plug and roasting it.

I replaced the injectors with cheapo import injectors.. melted another glow plug. Thought, well, that’s what I get for buying cheap injectors.

I replaced the cheap injectors with Delphi injectors.. melted two more glow plugs.

Start box is operating normally. I’ve metered the glow plug lead to verify that it’s not sending power non stop or anything weird.

Exhaust has a greyish smoke, smells of unburnt diesel. Truck otherwise seems to run fine.

Is it possible the Injector pump is sending too much pressure down that line? Would “turning down” the fuel at the pump be a possible option? Or is this perhaps just a timing issue?

Any thoughts or suggestions appreciated!

 

[frauhansen]

Switch the connectors with the glowplug next to it. When the issue travels with the connector, you will know that the injector is fine.

 

[MarkM]

Switch the connectors with the glowplug next to it. When the issue travels with the connector, you will know that the injector is fine.

Excellent suggestion !

You beat me to it lol

Mark

 

[frauhansen]

You beat me to it lol

I can look into the future, I'm 6 hours ahead of you

 

[Dieselmeister]

You say "melted". Are they just burning out, or are they actually melted?

 

[Humpty]

You say "melted". Are they just burning out, or are they actually melted?

Brittle and melted off. What’s left of them look like they were made of glass and were broke off.

 

[Humpty]

Switch the connectors with the glowplug next to it. When the issue travels with the connector, you will know that the injector is fine.

It is my understanding that the glow plug power is all parallel.. whatever power is sent to one they all get. I’ve metered the glow plug connectors, they all provide just over 23v during the wait period, then pulse immediately after starting then go to 2.3mv.

 

[REF]

If the injector is known to be good but looks wet when you pull it out you may want to check compression on that hole.

 

[Humpty]

If the injector is known to be good but looks wet when you pull it out you may want to check compression on that hole.

I know that the cylinder has compression because it has on two occasions blown the remainder of the glow plug element out of the hole leaving only the threaded in part.. sounded like a .22 round followed by a “Chitty Chitty Bang Bang” impression. it may not have *sufficient* compression however. I’ll have to check that.

 

[Mogman]

I know that the cylinder has compression because it has on two occasions blown the remainder of the glow plug element out of the hole leaving only the threaded in part.. sounded like a .22 round followed by a “Chitty Chitty Bang Bang” impression. it may not have *sufficient* compression however. I’ll have to check that.

I would not think low compression would be an issue, too much maybe..
I have never heard of an injector burning up a glow plug, I am not sure how that would even be possible.
Does the engine run good with no unusual noises or knocks??

 

[Humpty]

I would not think low compression would be an issue, too much maybe..
I have never heard of an injector burning up a glow plug, I am not sure how that would even be possible.
Does the engine run good with no unusual noises or knocks??

The theory was that fuel was accumulating on the glow plug and that during the normal glow plug heat cycle the fuel was igniting and that was what was roasting the glow plug. They end up looking like they were made of glass and snapped off. Very sooty as if they’d been in a fire. As to how it runs, it starts super easy and idles fine.. sounds fine anyway. It

 

[MarkM]

Could there be pieces of the old glow plugs blocking the passage in the precup?

 

[REF]

I went out to start my rig one day, turned the switch to run and in a couple of seconds heard a bang (sounded like a 22 going off) started looking and testing since I didn't even crank the engine. I focused on the glow plugs sure enough the plug in #2 cyl was bad so I pulled it and found the tip was missing. I pulled the injector to try and fish the tip out and found the injector was wet with fuel. I put the injector on the tester and it was bleeding fuel out the tip. Replaced the injector and glow plug and have had no further problems.
My best guess, is that the injector leaked fuel into the pre-cup and when the glow plug heated up it went bang. but it is possible that a glow plug just popped and I found the injector problem while i was there. You be the judge.

Now if the injector is wet with fuel (instead of soot) when you pulled it out and the injector has a good pattern / pop, and is not dribbling. Then you may have a low compression situation at an idle. Once the glow plugs quit cycling its up to compression to ignition the fuel. Min Compression at crank is 385PSI ref TM.

Just my best guess

 

[Humpty]

Here’s what the glow plugs in the offending cylinder end up looking like..

 

[Humpty]

I went out to start my rig one day, turned the switch to run and in a couple of seconds heard a bang (sounded like a 22 going off) started looking and testing since I didn't even crank the engine. I focused on the glow plugs sure enough the plug in #2 cyl was bad so I pulled it and found the tip was missing. I pulled the injector to try and fish the tip out and found the injector was wet with fuel. I put the injector on the tester and it was bleeding fuel out the tip. Replaced the injector and glow plug and have had no further problems.
My best guess, is that the injector leaked fuel into the pre-cup and when the glow plug heated up it went bang. but it is possible that a glow plug just popped and I found the injector problem while i was there. You be the judge.

Now if the injector is wet with fuel (instead of soot) when you pulled it out and the injector has a good pattern / pop, and is not dribbling. Then you may have a low compression situation at an idle. Once the glow plugs quit cycling its up to compression to ignition the fuel. Min Compression at crank is 385PSI ref TM.

Just my best guess

My 2 pops both happened when I was accelerating from a stop. This is my third injector.. so i’ve pretty much ruled out having a drippy injector. I’m going to grab a Harbor Freight diesel compression tester and check that cylinder. I have a feeling i’m going to find less than ideal compression on that cylinder.

 

[REF]

Well, If the piston collapsed and pinched the rings ( from getting hot or either used to start it) you should see a fair amount of blow by. I would not think head gasket because if it blew out you would hear it and if it blew between cylinders you would find low comp in both. Burnt, bent, stuck valve not closing completely could do it but should hear popping in the intake or exhaust (but these engines are noisy enough it may be hard to hear.
But lets not get ahead of our self's, Run compression test through the glow plug hole on that cylinder and the one next to it for a comparison and see what that shows you.

 

[Humpty]

Well, If the piston collapsed and pinched the rings ( from getting hot or either used to start it) you should see a fair amount of blow by. I would not think head gasket because if it blew out you would hear it and if it blew between cylinders you would find low comp in both. Burnt, bent, stuck valve not closing completely could do it but should hear popping in the intake or exhaust (but these engines are noisy enough it may be hard to hear.
But lets not get ahead of our self's, Run compression test through the glow plug hole on that cylinder and the one next to it for a comparison and see what that shows you.

I can tell you that taking the oil cap off and putting my hand across there isn’t any blowby there. I ordered a diesel compression set off Amazon for $40 delivered that’ll be here Wednesday I’ll check it then and let you know what I find out.

It won’t let me post a video of it running here - I’ll see if I can get one uploaded to my server and post a link. It somedays certainly *feels* zippier than other days.. i’d wondered if maybe I had a sticky valve but some folks in another group i’m in acted like that was crazy. lol

 

[kendelrio]

To piggyback on the "swap lead", it's possible you're getting a lot of amperage at the glowplug. I'd swap the lead just to make sure. Could be a bad wire. Swapping it would definitely rule out the wire or confirm it.

 

[Humpty]

To piggyback on the "swap lead", it's possible you're getting a lot of amperage at the glowplug. I'd swap the lead just to make sure. Could be a bad wire. Swapping it would definitely rule out the wire or confirm it.

That’s not how electricity works. A “bad wire” would provide low or no voltage to the glow plug. The same amperage and voltage is delivered to all the glow plugs, just like in your home wiring. All the outlets have the same amperage available. Your cell phone charger doesn’t bake because it is force fed 15 amps. The connected device determines the amperage draw.

The only way a start box is baking a glow plug is if it continuously providing 24 volts, and if the start box were doing that it would affect all the glow plugs since the plugs are wired in parallel. No other plugs are affected and i’ve verified with a meter that the start box is not continuously powering the glow plugs at this or any other cylinder.

 

[kendelrio]

That’s not how electricity works. A “bad wire” would provide low or no voltage to the glow plug. The same amperage and voltage is delivered to all the glow plugs, just like in your home wiring. All the outlets have the same amperage available. Your cell phone charger doesn’t bake because it is force fed 15 amps. The connected device determines the amperage draw.

The only way a start box is baking a glow plug is if it continuously providing 24 volts, and if the start box were doing that it would affect all the glow plugs since the plugs are wired in parallel. No other plugs are affected and i’ve verified with a meter that the start box is not continuously powering the glow plugs at this or any other cylinder.

I dunno... I seem to be smart enough to check glow plug leads before changing injectors 3 times, but that's just me...