Glow Plug Questions

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rmesgt

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I have never owned a diesel truck before and I have a few questions regarding the glow plugs that you folks might be able to answer.

I am guessing that when the key is turned on and the WAIT light is active, the glow plugs are heating up, but do they ALL glow or is it possible that some work properly and others are broken or fail?

If some of the eight glow plugs can fail and the others work, how does a person determine which ones work and which do not?

I have read some of the glow plug posts and have learned that I might need a Glow Plug Extraction Tool. I have watched several youtube videos and they all seem to recommend different tool. Which tool do you think is the best and should this tool be part of my toolbox?

The youtube videos also mention that sometimes the glow plugs break and that the tips must be extracted. The videos showed a person reaching into the engine with a pair of long handled needle nosed pliers. Is this problem to be expected or is it an anomaly?

How often should glow plugs be replaced? Is this an annual maintenance sort of thing?

Previous Glow Plug threads recommend the AC 60G plugs. Are these still the preferred glow plugs?

I have been reading other posts on the Glow Plugs and found where the moderator stated

This has been said many many times.

The stock GP sytem is supplied with 24v but, the combination of the resistors on the firewall and the resistance of 8 good glow plugs, in combination, drops the 24 volts supplied, to 12 volts(the voltage range of the glow plugs). If just one glow plug has a bad connection or goes bad, the rest will blow in succession(as the voltage will increase with each gp failure).

That's the bad thing about not converting to 12v supply.

Why don't you want to convert to 12v supply?

Should I consider changing my 24V to 12V?

Any answers to these questions will BE GREATLY APPRECIATED. Thank you all...









 

cucvrus

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I get by for 25+ years with the stock glow plug system. I have changed thousands of CUCV glow plugs in hundreds of CUCV's. I experienced 20 at most that broke off in the engine. The only extraction tool I ever used was a vise grips, spray lube, a crow bar and in the past a lot of cursing. I have removed inner fender aprons on a few to get stuck glow plugs out. Also have removed the diesel delivery nozzle from the cylinder effected by the broken glow plug. After that is out I used a curved jaw needle nose to extract the tip. Others have ways of checking glow plugs may and do differ. I open the hood and get a 3/8" deep socket and a ratchet and remove all 8 glow plugs. I visually inspect and test each one with a battery jump pack.

I try and not glow them red hot but if they smoke with a little oil on them after making contact on the jump pack they are good to go. I don't change all 8 when 1 or 2 go bad. Unless I am requested to do so. I have lasted many years on others used glow plugs. I received a 5 gallon bucket of used CUCV glow plugs one year from a friend and lived off of them for 20 + years. 99% were fine. Routine maintenance I guess. Uncle Sam has deep pockets. Others results may vary and do again. But I run the AC Delco 13 G and my customers all do along with company plow trucks. Which we are down to 2 at this time. CUCV's do and will wear out. Good Luck. I know others have different options for you. But I keep it simple and keep it stock. It lasted this long. Have a Great Day. Be Safe.
 
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Floridianson

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If some of the eight glow plugs can fail and the others work, how does a person determine which ones work and which one do not.


Myself for quick and easy test. Remove all electrical connectors from the top of the glow plugs. I get a 12 volt test light and hook the alligator clip to the positive terminal of the battery or a known 12 volt positive source. Then with the tip of the test light touch the electrical connection of the glow plug where the wire was. If the light lights up that plug is good if not it is bad and I only replace when one goes bad.
 
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rmesgt

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Thank you both for your responses. I wasn't sure how glow plugs behave. Someone stated that "They either work or they don't". indicating that they work great all the time until they quit. Another person stated that "They start out good but progressively get worse and worse until they no longer work" I believe that answers are somewhat correct. I am going to buy the test light (which I need anyway) and test them as James stated. The AC60G glow plug is about $9.30 each at O'Reilly Automotive and I would hate to sink $80.00 into parts I don't need...
 

dconn22

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I just did my first set, they [mine] were pretty easy to remove, they looked pretty new but still had two that had drooped and needed a visegrip and some gentle tugging to get those two out. Because of that and the connectors were ground to fit the stock wiring connectors which most of those were found to be in poor condition. I have decide to make-up new HD wiring new HD relay and am going to use a manual switch while I investigate the controller circuit [which I'm hoping to use].

I have also decided to eliminate the resistors and am going to run a 2ga cable directly from the front battery [12v] to the GP relay. I will eventually eliminate 24v entirely as I am restoring this to be a daily driver and not a collector/museum piece [new resistors are not available, and appear to be used only to reduce current draw during 24 volt jump starts. Plus, the 12/24 volt system can not be easily jumped by a 12v only vehicle. This is my first CUCV/diesel [3weeks] and am still learning so if anything I have said is flat wrong please feel free to correct me.
 
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richingalveston

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just replace the connectors with crimp on, Disconnect the wire from your resistor on the glow plug controller side and connect that wire to the 12Volt terminal block next to the glow plug controller,
buy a new glow plug controller card if needed and then add a push button if you so desire. the standard crimp connectors work fine with the AC60g glow plug.

A new harness is probably not needed and there is already a wire from the front battery to the 12 volt block. just use the correct fusable link on the wire from the 12volt terminal to the glow plug relay. you don't even have to remove the resistor unless you really want to.

once you get to know the wiring, there is no real need to change much
 

Tim Sothard

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I switched to ac60g’s and had to change my spade connectors to 1/4”. Also, I don’t know if this is crazy or not but last time I had a glow plug that didn’t want to come out I loosened it all the way, closed the hood,rolled the engine and let her fire out. Lotta compression works good!
 

rmesgt

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Another Odd-Ball question... If, say, four or five glow plugs are working, what happens in the cylinders with glow plugs that don't work? I guess that eventually, the mixture in these "failed plug" cylinders begins to ignite, but how? What happens if you only have two functional glow plugs? Would the truck actually start? I know the the larger trucks (5 tons, Wreckers, etc) don't need glow plugs as the heat generated in compression is enough to ignite the mixture. Does this hold true for the 6.2 diesels? Finally, is there a book or white paper that explains the process for 6.2 or 6.5 diesel engines? Thank you all for you assistance...
 

cucvrus

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Same goes for the CUCV diesel engine. Once ignited and running compression takes over on all cylinders. I can tell when my CUCV has a glow plug or 2 not working. I never had all 8 fail at one time. I never left it go that long. It I experienced a hard start I checked them all by removing them and doing a visual bench test on all 8 glow plugs. Even with no glow plugs and pipe plugs in the glow plug holes the CUCV diesel will run. Some are started for years with starting fluid and survive, I don't recommend it but yes they start. There is GM tech manuals available that explain the 6.2 diesel engine. Let me get a better description of the paper back manual and maybe some numbers off of it. I seen them for sale on the internet. Happy Holidays. Be Safe.
 

MarcusOReallyus

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I have also decided to eliminate the resistors and am going to run a 2ga cable directly from the front battery [12v] to the GP relay.

2 gauge is a massive waste of copper. You gain nothing by going that big.

See this thread for some facts and figures on current draw.

When you finally convert to 12v, remember to replace all of your battery cables. They need to be bigger if they are going to run 12v, as you'll need to pull more current through them. I've been very happy with custom cables from BestBoatWire.com.
 

rmesgt

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Thank you for answering my question about cylinder ignition. I didn't (don't?) quite understand the relationship between compression heat, glow plug ignition, etc. It seems to me that if all of the glow plugs are Full Mission Capable, the engine starts quickly. If some of the glow plugs have failed, the engine will start but it takes a bit. If the majority of the glow plugs have failed, the engine will start with great difficulty. Bottom line is - Check your glow plugs at each oil change. They either work or they don't. Are these conclusions correct? Please advise...
 

cucvrus

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I would start fresh and remove them all and get a visual on them. I check them with a jump pack and a little oil. Dip the tip in oil. Hook the negative to the threaded shaft. Touch the positive to the spade. It will or should smoke instantly. If not the glow plug is defective. And it should be the very tip about a 1/4" - 1/2" from tip. If it glows mid shaft it is scrap. But checking them every oil change is not necessary. Also many people blame glow plugs and the fact is that it could be fuel related. The injection pump is always danced around and because it is a $300-$500. item people will try and ignore that as the issue. The engine should start if the glow plugs work and fuel is in the chamber to be ignited. Checking everything and repairing as needed is the key to a reliable CUCV. Not redesigning everything as you go. That just adds to issues and deters help on diagnostics. Good Luck. Happy Holidays. Be Safe. I still buy and use 13G A C Delco glow plugs and swear by them over 24 years of CUCV use.
 

MarcusOReallyus

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I didn't (don't?) quite understand the relationship between compression heat, glow plug ignition, etc.
Okay, I'll try to take a stab at it. I'm no diesel expert myself, so if I get any of this wrong, I expect some of you pros to chime in and whack me.

Diesel fuel is much less volatile than gasoline. It takes a lot to ignite it. Toss a cup full of gas on the pavement, and toss a lit cigarette onto it, and it will probably go whoosh. Do the same with diesel, and.... nothing. Nope.

That means our familiar spark plug is probably not going to get the job done in a diesel engine.

So, we rely on compression to make enough heat to ignite the diesel fuel. When a gas (like air) is compressed, it heats up (see video below). The more it is compressed, the hotter it gets. That's why diesel engines have (need!) far more compression than a gas engine.

Also, the more rapidly it is compressed, the hotter it gets.

So we need two things to start a diesel engine: high compression, and rapid compression.

But sometimes that's not enough. On a cold engine, the compression just might not be enough to get the fuel/air mix hot enough to ignite.

So we cheat. We add glow plugs to the mix. The GPs heat the air in the combustion chamber enough to BOOST the heat provided by the compression. They don't ignite the fuel the way a spark plug does. They just add some HEAT to the process.

That's why the controller has a temperature sensor. If the engine is warm, no sense in firing the GPs. If the engine is really cold, we need to fire them longer to add more heat. (Thus, the Wait light!) That's also why the controller may sometimes fire the GPs when the engine has already started. It's called afterglow. It's just helping things along.
So the GPs are a heat booster.
So let's put this all together:


  • If your GPs (or some of them) aren't working, your engine will struggle to start (unless you are in the Sudan at 125 degrees, maybe!).
  • If your starter isn't turning over rapidly enough, your engine will struggle to start. (Bad batteries, starter, etc.)
  • If your compression isn't high enough, your engine will struggle to start. (Rings are shot, cylinders are worn, etc.)
  • If your fuel isn't being atomized enough, your engine will struggle to start. (fuel system problems)

That's not an exhaustive list, I suppose, but I hope it gives you the general idea. Anything that interferes with the compression, the rate of compression (how fast it turns over), the fuel delivery, or the heat in the cylinders, will make your engine struggle to start.

And, of course, if bad enough, will prevent starting.

https://www.youtube.com/watch?v=ttz-CzEDXwI
 

rmesgt

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Your reply to my post is pure genius! I didn't understand the relationship between the glow plugs and the necessary heat to ignite diesel fuel. I was thinking of the glow plugs as "Spark Plugs" rather than a heat booster. You explained everything so well, I think I could now explain it to others. As with every machine, each system (or sub system) is critical to the overall success of the total machine. I can see how the failure of one sub(sub)system (fuel delivery, for example) will negatively impact the subsystem (ignition, in this case), which in turn degrades the entire system (my CUCV). This reminds me of the poem "For the want of a nail" {Benjamin Franklin}.

Thank you for taking the time to explain this to me. You (and the others on this forum) are brilliant.
 

chevymike

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Great post MarcusOReallyus. Just for reference that glow plugs are not needed, Cummins engines do not have glow plugs. They use compression only (well and a heating grid in the intake but many remove/disable that due to issues).
 

dconn22

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I have read several posts indicating that the amp draw on the AC plugs is between 12-15 each with initial "rush-in" amps up to 22 momentary(12 voltz). Multiply that times 8 and... The current wiring looks like it has been warm more than a few times so I am retiring on the side of more capacity. Also will be supplying the 12v "bus" through this via the GP relay terminal, the primary wire currently supplying it looks 30+ years old. Haven't figured all the details yet.
 
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