I have a skoda superb 2.0 tdi CFFB.

 

Here in denmark, A LOT ogf people have A LOT of different meanings about closing egr with the CR engine.

 

Is here an expert that can really tell me what is happening ?

 

Lot of tuners say, that EGR must not be closed, as the regen will be disturbed. Why ?

 

Another bunch - the more experienced tuners i think, say it can easily be done, it just has to be done correctly. True ?

 

I also no a lot of drivers, which had had their cars optimized and also egr off, then they drive 3 weeks, and the dpf lamp comes on. It has never before turned on.

 

Will closing of the egr leads to more or less soot in the dpf ? I have always thought that egr off would lead to more soot particles in the dpf, end there fore more frequent regen ?

 

Now one of my friend showed me his dpf app from his car, a 2.0 tdi 170 CR, and the claculated soot rises as i drives, but the measured soot stays around zero!! So he is claiming, that because he has done egr off, no soot ends in the filter, and the filter just goes through regen when calculated soot hits 18 grams, but in reality there is no soot to burn off ???

He also showed me this graph, which he considered kind of proof that it works, because soot and nox is opposite dependant on eachother. And the egr valve in function is to reduce nox, and therefore creates more soot - and when you then make egr off you will raise the nox, but lower the soot. Im really relly confused. If my dpf behaves like normal with 400 miles between regen, i will do the egr off, but if it gets the dpf to act up, i will not do it.

My CFFB runs on standard engine software, and not the noxfix.

 

Soot and CO2 are not the same thing, but it is true that EGR valves are there to reduce NOx, and in doing so they will increase particulates/soot creation.

 

The trouble with trying to change the system on recent engines is that it's all tightly controlled to work together, so removing one system (like EGR) will probably upset other parts (like the DPF). It's usually also illegal to change any part of the emissions systems.

I'm no expert but my understanding is that the EGR should be left in place if you have a DPF which is inline with Darksides (a well regarded UK tuner) view: https://www.darksidedevelopments.co.uk/diesel-particulate-filter-dpf-fap/

 

Quote

The EGR Valve CANNOT be removed on vehicles that still have the DPF Filter present, doing so would soon block the DPF.

 

I agree that the EGR can be used to balance NOx vs soot production as it's one of the tweaks used by the 'emissions fix'. By increasing EGR use, combustion temperatures are lowered (less oxygen) which produces less NOx but extra soot. This is why post-fix cars have had both EGR and extra regen issues.

 

Closing or blanking the EGR should increase NOx but reduce soot production. However, it will still produce soot and the soot can only end up in the DPF. If your friends car is reporting zero soot measured, it suggests it's had more than just an EGR delete. Just think about how much soot an older diesel without a DPF throws out on full throttle - it has to go somewhere...

 

The ECU is constantly adjusting the EGR but during a regen I'd expect it to be mostly shut to help raise exhaust temperatures. It's certainly plausible that the EGR could be used to fine tune the exhaust gases/temperatures to make the DPF regeneration more efficient or quicker.

 

Why are you considering having the EGR blanked?

Rather than write it all out again, I discussed EGR functionality and NOx formation here in reasonable depth:

The graph in the OP's post shows the relationship between injection timing and formation of CO2 and NOx (relative to fuel consumption). Earlier injection means more complete combustion of the fuel, lowering CO2 production per litre of fuel used. The more extreme temperatures and pressures reached during this complete combustion increases NOx. It has nothing to do with EGR or DPF functionality.

I had a few posts in this thread that got theory heavy too if you're interested: