What causes the 9th injector to clog and affect the regen cycle?

[DieselDaily]

I’ve noticed my 2014 LML is going into regen much more frequently lately, and my fuel economy is tanking. A buddy mentioned the "9th injector" (hydrocarbon injector) in the exhaust might be leaking or clogged. If it’s not spraying correctly, WHAT happens to the DPF during the cleaning cycle? Is this something I can pull and clean with some carb cleaner, or is it a "replace only" part once it gets sooted up?

 

[SteelAndSteam]

The main cause of the 9th injector clogging is its location and the nature of diesel exhaust. Since it’s mounted directly in the exhaust pipe before the DPF, it’s constantly exposed to extreme heat and soot. Over time, a "carbon crust" forms over the tiny nozzle. If you do a lot of city driving or short trips where the exhaust doesn't get hot enough to naturally burn off that soot, the tip eventually gets completely blocked. When it clogs, it can't mist the fuel properly, so it either drips or doesn't spray at all, which is why your truck is struggling to complete a successful regen.

 

[DuramaxKid92]

When the 9th injector gets clogged with carbon, it can’t atomize the diesel fuel, or it stops spraying entirely. During a regen cycle, the ECM expects the exhaust temp to skyrocket to burn off the soot. If the HCI is clogged, the exhaust never gets hot enough to clean the filter. The truck will prolong the regen cycle, continuously pumping fuel down the exhaust in a desperate attempt to reach temp. This is exactly why your MPG is tanking—the truck is stuck in a 'lazy' or perpetual regen loop, and the DPF is slowly choking to death on soot because it’s never getting baked.