92 M998 6.2 hard to start

[Jtbaker1989]

Hey everyone. Kind of a background story real quick, I work as a tech at a Chrysler dealership. A guy traded a M998 in and the owner has kept it. Traded in this past summer and haven't had any issues until now.
this may be a long post so forgive me for all the reading.
A few days ago the truck wouldn't start. Been parked outside. WTS light would come on, could hear a relay click on under steering wheel. WTS light would stay on for about 10 seconds and would go out. Engine would crank but wouldn't start. White smoke out tail pipe which made me believe it was raw diesel fuel. After 15 minutes of cranking and messing around with it, it finally started. Right before it fired up, white smoke turned to gray then to black right as it fired. I drove it back to the shop which is about a 10 mile drive and it ran perfect. No smoke, no surging.
Shut the truck off and re-started. The starter didn't stay engaged for a second before it started. First thought was glow plugs. Let the truck sit overnight in shop which is about 65ish degrees when we aren't there. It still takes about 15 seconds of cranking before engine starts. Smoke stays the same. White then gray then black right as it starts.
I do have knowledge about diesels but not much when it comes to glow plugs. All of our trucks use heater grids. I started to check the glow plug system out. All 8 look new, the "smart start box" under steering wheel looks brand new, coolant temp sensor on RT side of engine intake manifold with harness going to it looks brand new.
When ign switch is turned on, I have 24v at glow plugs. I took a test light and went from battery + to each glow plug and test light came on. A few things I, not sure of is: am I testing the system correctly? When engine starts I still have 27v present at glow plugs. Even after engine has ran for a few minutes. Are they supposed to stay on that long?
So in the end I'm not sure if I'm dealing with a fuel delivery issue or something else. No fuel leaks. There is a valve on the LT side of engine bay next to washer tank that runs to fuel filter. If I crack that line open fuel runs out even after it has sat for a extended period of time.
Problem seems to be when engine is cold. If you let it idle for 5 minutes it will start back perfect.
Again I'm sorry for the long post, thank you for the time and help.

 

[diesel dave]

Sounds to like some of your glow plugs are bad. I'm not sure you checked them correctly. Although I've not checked Hmmwv glow plugs,I have checked them on cucv's with a test light. Did you unhook the wire to each plug before checking? If you pull them and they are swollen,they are probably bad,at least that was my experience with cucv's.
if one is bad,replace all.

 

[BLK HMMWV]

To answer part of your question.
Yes depending on what control box you have the glow plugs will cycle for a few minutes after the engine is running.
You may notice the charging gauge pulse for a few minutes after engine starts .It is my understanding that that is normal with some control box's and that is also related to the glow plugs.
Do a search for glow plug resistance. Check each one with engine off.
If they are bad and your going to replace them make sure you buy the correct glow plugs for 24 system (military) not 12 volt (Civilian hummer)
Also research swollen glow plugs. You may need a special tool to remove them.

 

[1 Patriot-of-many]

Glow plugs need to be tested with an ohm meter. Can't remember but I think they are supposed to be 2 ohms to 5. It's in the TM's Mine all tested in the 3 ohm range, almost brand new plugs. 1.5-5 ohms Do a search for hmmwv_test-diagnostics. There's a .pdf floating around here somewhere, I didn't see it in the TM section.

 

[Jtbaker1989]

Thanks for the info. I unhooked each glow plug before using a test light going from battery positive to each plug.
Do you guys prefer to ohm check them by removing them fully or just going from the exposed tip to ground?

 

[BLK HMMWV]

tip to ground will work however if they are already out I'd just replace them.

 

[Jtbaker1989]

Thanks. 1-Patriot-of-many thank you for that PDF link. Google search found it. That will be a big help

 

[Jtbaker1989]

They "look" new. I will check the resistance of them tomorrow and maybe see how well they want to come out. I kinda thought something had been messed with bc all the glow plug connectors have been marked

 

[BLK HMMWV]

You may want to apply a little bit of Hi-temp anti seize to them when you re install them or new ones

 

[Jtbaker1989]

I looked at that PDF and came across the "cold start advance switch". It really doesn't give much description into it just how to test it.
I assume it has to do with advancing the fuel timing when cold. Is this correct?

 

[hatzie]

I looked at that PDF and came across the "cold start advance switch". It really doesn't give much description into it just how to test it.
I assume it has to do with advancing the fuel timing when cold. Is this correct?

On the civilian 6.2 the HPCA is engaged by 12v connections on the injection pump til the engine is over the set temp of the thermal switch. It restricts fuel return to raise the housing pressure to give @3 degrees of advance.

There's a glow inhibit thermal switch as well. Theory of operation is in the 6.2l bible (GM Service Training Textbook), I scanned several years ago. It's been posted in the CUCV TM section along with scan of the 6.5l textbook.

Sent from my SM-P605V using Tapatalk

 

[Jtbaker1989]

Good morning. I got around to messing with this humvee some more. So far i have only messed with two glow plugs. The first one unscrewed very easily but it doenst want to come out. Turns easy but just wont pull out. Not sure if theres just alot of soot built up on the tip or the tip is bent over.
The glow plug that i did get to come out ohms at "OL". Thats going from the tip of the plug to the threads just like the manual shows. So i would assume i have a glow plug issue. They "look" new, which kind of worries me. Could there be another issue in the system that is causing premature failure of the plugs?

Also, what are some recommendations on getting plugs out that do not want to come out? The one that did come out had soot built up on it, i just kept wiggleing it and it finally pulled out. Thanks for the time and help

 

[Wire Fox]

Good morning. I got around to messing with this humvee some more. So far i have only messed with two glow plugs. The first one unscrewed very easily but it doenst want to come out. Turns easy but just wont pull out. Not sure if theres just alot of soot built up on the tip or the tip is bent over.
The glow plug that i did get to come out ohms at "OL". Thats going from the tip of the plug to the threads just like the manual shows. So i would assume i have a glow plug issue. They "look" new, which kind of worries me. Could there be another issue in the system that is causing premature failure of the plugs?

Also, what are some recommendations on getting plugs out that do not want to come out? The one that did come out had soot built up on it, i just kept wiggleing it and it finally pulled out. Thanks for the time and help

They're probably swollen. This tool, or another similar to it, should take care of you: https://www.real4wd.com/zedSuite/catalog/partdetail.aspx?PartNo=GPRT

 

[1 Patriot-of-many]

http://www.jjandaracing.com/contents/en-us/d9.html Make sure you get 24V glow plugs. I have the Delco 15G's in mine, wellman is another brand lots of people use. If you break a tip off the glow plug pulling them, prepare for some fun........ Look new doesn't mean a **** thing Yes some boxes have been known to keep the glow plugs on when the box failed. 15G's are supposed to be self regulating from what I've heard. Good luck, hopefully they all come out without breaking a tip off. I broke a tip pulling my last one out, didn't realize it when the plug fell under the truck. Didn't look at it till I p[ut the new plug in and started the engine.....Talk about a racket!!!!!! The tip fell down into the cylinder. Luckily after a few seconds of running I could tell the tip hung up the exhaust valve and went through luckily into the exhaust pipe. I don't recommend that approach to removing the broken tips.....

 

[Jtbaker1989]

Thanks alot. I kept messing with that one and it finally came out. Looks like it was just sooted up enough to cause a issue. Still have 6 to go tho lol. Looking at the one of the plugs the numbers that are on it are: 19207-12338771 and MRF-3HCM3. On the hex head part there is 174. No clue what they mean or if you can tell anything by them. I will start with a set of plugs and go from there. Thanks everyone for the help. Yall are making my life alittle easier!

Is there a certain website or certain company that i can call to get the correct plugs from?

 

[Wire Fox]

Thanks alot. I kept messing with that one and it finally came out. Looks like it was just sooted up enough to cause a issue. Still have 6 to go tho lol. Looking at the one of the plugs the numbers that are on it are: 19207-12338771 and MRF-3HCM3. On the hex head part there is 174. No clue what they mean or if you can tell anything by them. I will start with a set of plugs and go from there. Thanks everyone for the help. Yall are making my life alittle easier!

Is there a certain website or certain company that i can call to get the correct plugs from?

Price is just a little bit high here, but they would be the right part for sure: http://www.hummerpartsguy.com/GLOW-PLUG-24V-SET-OF-8-HMMWV_p_14724.html Just make sure that you're buying a 24V plug, NOT a 12V plug. Amazon, eBay, Kascar, Erick's Military Surplus, Adventure 4x4, NAPA, and most part stores should be able to find these. Wellman is the commonly-used brand that I've seen.

 

[Jtbaker1989]

Hey everyone. Finally got around to messing with this humvee and it hasnt turned out good at all.
I got 7 of the old glow plugs out and ohm checked each one. all 7 were showing OL. The 8th one i could not get out and was afraid i was going to break it.
I ordered a set of plugs from hummerpartsguy and double checked they were 24v plugs. Got 7 of them installed yesterday(16th) truck started great. Engine didnt even turn over twice before it started. Today(17th) i come in and try to start it. Now its back to its old ways. Taking about 15-20 seconds to start.
WTS light comes on as well. So i decided to pull a plug out and test it to see if it was okay. I can NOT get any of these plugs out now. They are extremely tight even after all the threads are out of the head. I ohm tested them again from tip to threads and so far two of them show OL again.
It looks like this thing is burning up plugs and i have no clue why and now im not sure how im going to get these out without breaking them.

 

[fllaw1]

You need to clarify what box you have under the dash. Just because it looks new it can be an original and not a smart start converted one. So many posts on cooking the plugs. The line you referred to is the fuel vent line next to the coolant resovoir.

 

[BLK HMMWV]

You most likely have a bad control box.
You will most likely need to buy or borrow the tool to remove the swollen glow plugs.
Hopefully you don't break the tip off inside the head other wise you will have some real fun.
Have you ready through all of the sticky's listed on the top of the HMMWV section.
The 4th one down may help you out .
It is the one titled LEO /FD check list.
Read down it and you will come to some good info regarding control box's.

Hope that helps
BH

 

[NormB]

You may want to apply a little bit of Hi-temp anti seize to them when you re install them or new ones

You DEFINITELY need to apply some high-temp anti-seize on those things.

This is good: https://smile.amazon.com/dp/B0002UE...F8&qid=1484699076&sr=sr-1&keywords=anti-seize