Post Injection of fuel (not during regen)?

[muddyboots]

Hi all

I have a 2021 CXEC 199ps 4motion, recently bought.

As with most of my cars I've been nerding around with VAG-DPF just to get a feel for what's normal.

I noticed that I'm nearly always seeing Post Injection 3 quantity at around 5mg/str. Only drops to zero on no throttle or full throttle. This is not during a regen, and exhaust temps are normal (e.g. circa 250° on a motorway cruise).

Previous cars have only ever had Post Injection 3 qty above zero when cold, or during a regen.

Also noticed mpg barely exceeds ~33mpg on steady legal motorway cruise, and also the calculated and measured soot values rise almost continously so I get maybe 200-250km between regens.

Wondered if anyone else has ever observed Post Injection 3 above zero during normal driving conditions?
Seems odd to me and presumably could explain rubbish economy...

 

[manfrotto]

Interesting question.
I doubt anyone on the forum would be looking that closely at parametres like that (with the exception of maybe @mmi )

My last blockmap (single snapshot at idle) was showing 0 mg/stroke if that is of any help

 

[manfrotto]

I just remembered that VAG DPF (Lots on here have this app) reports on post Injection 3 quantity, so maybe someone can report what there app shows.

 

[Dellmassive]

 

[Dellmassive]

More pics over here...

Thread 'DPF Regen, Yellow Light & Adblue - Whats It All About? -'

16 Mar 2019

DPF Regen, Yellow light & AdBlue - Whats it all about? -

The DFP light is becoming a more apparent issue with modern diesel vans, unfortunately, it’s a fact of modern diesel life.




what is a DPF?

Diesel particulate filters (DPF) are very effective in cutting emissions, trapping even the finest soot particles produced as the engine burns diesel fuel.
Their lifespan is dependent on factors such as fuel quality, driving style, use and oil consumption. The filter uses a catalytic coating containing precious metals. Passive regeneration converts the particulate matter...

• Dellmassive
• adblue dpf euro 6 regen
• Replies: 78
• Forum: Engine, Gearbox, Exhaust, Drivetrain

• 

 

[DXX]

If it’s working it doesn’t need fixing.

 

[mmi]

Previous cars have only ever had Post Injection 3 qty above zero when cold, or during a regen.

Did they have the same Delphi ECU?

I noticed that I'm nearly always seeing Post Injection 3 quantity at around 5mg/str. Only drops to zero on no throttle or full throttle. This is not during a regen, and exhaust temps are normal (e.g. circa 250° on a motorway cruise).

I believe the CXEC is in this respect identical to CXEB engine (as well as with all T6 EU6 engines). So perfectly normal throughout.
Below a graph of the "Post 3 quantity" both outside DPF regen and inside DPF regen (at falling soot level).

 

[muddyboots]

Thanks - really useful, so it appears to be normal behaviour then.

I still remain curious as to what post-injection of fuel is being used for. All my previous VAG diesels have only ever used it to raise exhaust/DPF temps for regen, or to quickly warmup from cold start.
Here, it's happening outside of regen when everything is fully up to temperature, and when the engine is under some load and therefore chucking out hot exhaust gas, so I assume it can't be to do with raising temperatures.
I guess it's something emission related, but would love to know more detail if anyone knows, perhaps there's an SSP that explains it.