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Ok, so I'm rolling along in my baby Duramax Colorado doing between 35-45 in fairly heavy traffic and I smell this horrible smell like I'm following a poorly running public bus or quad axle dump truck. Then, as I travel along basking in the essence of that foul smell from the nether regions of perdition, I realize some 10-15 minutes later that this may be the regen I hear spoken of. Oddly enough, it was running fine and had good power. By the time I was on the home stretch just a few minutes hence, the smell was gone. Weird.
 

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When the truck is going through a regen, it will probably operate better than. You are tuned so it may be harder to tell than a stock truck, but during regen the EGR closes so if you go to accelerate, it will feel more responsive.
 

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Good to know. I kept looking around for a large Semi truck or some such thing and going, "that can't be me", "must be some other guy".
 

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One thing that I have had happen and heard others discuss happening with their trucks, is white smoke during regens. It does not happen every time, but it seems more likely to happen in cool weather.

The explanation I heard from tuner GDE that makes sense is that the 5th injector starts injecting diesel into the system a little early and before the system is fully up to temp and ready to burn it off. This is a programming issue from the factory and not really a big deal, except a little embarrassing if you happen to be smoking out traffic behind you for a minute or so. Pehaps GM fixed the issue with recent ECM programming updates.
 

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One thing that I have had happen and heard others discuss happening with their trucks, is white smoke during regens. It does not happen every time, but it seems more likely to happen in cool weather.

The explanation I heard from tuner GDE that makes sense is that the 5th injector starts injecting diesel into the system a little early and before the system is fully up to temp and ready to burn it off. This is a programming issue from the factory and not really a big deal, except a little embarrassing if you happen to be smoking out traffic behind you for a minute or so. Pehaps GM fixed the issue with recent ECM programming updates.
I'm not sure there's such a thing as a 5th injector on the 2.8. The way I understand the regen to work is they use more fuel and stop using EGR which raises EGT to burn off the soot in the DPF. I've even heard that they use a secondary injection to intentionally dump raw fuel into the exhaust stream so it can be catalyzed by the SCR to raise EGT regardless of how the actual engine is running.

One side effect is that it needs to use more DEF to reduce NOx created by the high combustion temps. Given that DEF is 1/3 water, most of the white "smoke" you see is actually steam. Otherwise, white smoke is usually either a sign of a blow head gasket and coolant running through the engine cresting steam, or vaporized and completely unburned fuel, which with diesel usually means a cylinder has zero combustion taking place (because partial diesel combustion produces soot, which as we know is black/dark brown).

I believe the "big trucks" use a 9th injector (or 7th in the case of a Cummins?) because unless you're towing, moving the vehicle down the road is such a light load on those big engines it has a really hard time raising EGT to what it needs to be to clean the DPF. And also because raising combustion temps in the cylinder would create so much NOx, they'd use an unreasonable amount of DEF to bring it down to levels acceptable by the EPA.

The 2.8 doesn't have this issue because it's working decently hard to move our 4600 lb trucks down the road.

Of course, this is all based on 3rd hand info I've read on the Internet and the basic principles of diesel combustion as I understand it from my schooling, so I could be wrong about a lot of this.
 

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I'm not sure there's such a thing as a 5th injector on the 2.8.... One side effect is that it needs to use more DEF to reduce NOx created by the high combustion temps. Given that DEF is 1/3 water, most of the white "smoke" you see is actually steam.
Glad you posted, it caused me to have a realization I think is helpful. My truck has a GDE tune and the past setup had DEF injection turned completely off. The final tune, which I manged to snag just before the EPA storm troops moved in, reactivates DEF injection. I like having DEF injection turned on as this negates having to drain stale DEF from the tank, and I suppose it reduces NOx at least some. I was also concerned about the DEF injector itself, as mechanical items that are not used tend to fail after awhile, which would generate a code, even with the tune.

The realization occurred as my truck never had white smoke before during regen, as there was no DEF injection to cause it due to the tune. Now, with DEF turned back on, one time on a cool day it did billow out a bunch of white steam like you described. I suspect extra DEF being injected during regen is indeed the cause of the smoke, and while annoying if it happens, it is completely harmless. Have monitored other regens via OBD fusion and not seen any visible steam or smoke at all, so it seems a bit random when it happens.

Our trucks have a fuel dosing injector ahead of the DPF for adding fuel during regen like the big boys do, and that is awesome and much better than post combustion injection of fuel into the engine itself, which can cause oil dilution problems. They call the part an "indirect injector". The part is the same one used in the big Duramaxes per the compatibility table.

https://www.ebay.com/itm/Indirect-Fuel-Injector-ACDelco-GM-Original-Equipment-12641278-/152871262296
 
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Glad you posted, it caused me to have a realization I think is helpful. My truck has a GDE tune and the past setup had DEF injection turned completely off. The final tune, which I manged to snag just before the EPA storm troops moved in, reactivates DEF injection. I like having DEF injection turned on as this negates having to drain stale DEF from the tank, and I suppose it reduces NOx at least some. I was also concerned about the DEF injector itself, as mechanical items that are not used tend to fail after awhile, which would generate a code, even with the tune.

The realization occurred as my truck never had white smoke before during regen, as there was no DEF injection to cause it due to the tune. Now, with DEF turned back on, one time on a cool day it did billow out a bunch of white steam like you described. I suspect extra DEF being injected during regen is indeed the cause of the smoke, and while annoying if it happens, it is completely harmless. Have monitored other regens via OBD fusion and not seen any visible steam or smoke at all, so it seems a bit random when it happens.

Our trucks have a fuel dosing injector ahead of the DPF for adding fuel during regen like the big boys do, and that is awesome and much better than post combustion injection of fuel into the engine itself, which can cause oil dilution problems. They call the part an "indirect injector". The part is the same one used in the big Duramaxes per the compatibility table.

https://www.ebay.com/itm/Indirect-Fuel-Injector-ACDelco-GM-Original-Equipment-12641278-/152871262296
That makes sense, because that's originally how I understood regen to work, even in these little engines, but I was never able to find a component diagram that shows it. Now that I have a Quickjack, next time I have it up in the air I'll see if I can put eyes on it on my own truck.
 

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That makes sense, because that's originally how I understood regen to work, even in these little engines, but I was never able to find a component diagram that shows it. Now that I have a Quickjack, next time I have it up in the air I'll see if I can put eyes on it on my own truck.
96[/QUOTE]

I'll save you a crawl on your cold garage floor. Scroll to 7:40 in this video to see the indirect fuel injector. The video starts going over the after treatment system at 7:00, and it does a nice job.


I do accept virtual cold beers :D
 
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"I would never tell you to delete your truck." Nodding yes through entire sentence.
 
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