I have a Focus Mk3 2014 1.6Tdci with 75k miles on the clock. It just failed the MOT emissions test - exhaust gas opacity too high.

I'd already put 400ml of Forte DPF cleaner in about a week before. On the advice of the MOT mechanic, I took it for a drive up the motorway in 3rd - 3500/4000 rpm and it just scraped through the retest. 

I still don't think it's right though - the exhaust pipe is sooty and if you watch the exhaust while someone else blips the throttle you can see a bit of black smoke. I had the same problem at the last MOT, but the one before that was fine.

We don't normally do many long runs - just a daily 2 x 8 miles ride and the mechanics think that this is the problem. But surely the whole point of the DPF is that it is meant to stop ANY black smoke particles getting through? I could understand if the problem was the DPF getting blocked up, but that does not seem to be the case. Could it be that there is a crack in the DPF?

I've had a look with Forscan and no relevant DTCs are showing up. I've also looked at what I think are relevant PIDs when stopped, idling and at 3000rpm (parked up).

 

 

 

 

Any help appreciated.

So I checked with Forscan one week later and DPF_SOOT_LD had gone up to 54%:

 

 

I'm just wondering if this is normal and once that PID value reaches a certain higher figure then a regeneration will occur? Though I have seen other posts referring to DPF_LOAD as the PID that increases in the short term.

I've still got the fundamental problem of high smoke levels though - the exhaust still looks sooty.

I did hope we had some DPF experts on here who might be able to help.....

I seem to have become an absolute expert in the art of creating posts that get no replys!

And all without any formal training!

Lance

I think your Mechanic is correct, if you do mostly short trips then your DPF will soot up. 

Just for info, the Inferred Soot Load is exactly what is says, it is an inferred value not a measured one. Open  Loop is before the engine reaches its full operating temperature, so the high readings for this would suggest that the car spends a lot of its time doing short journeys.

The Differential Pressure is a measured value and is the one to keep an eye on. I noticed that it went up from 0.2 to 0.4 in your second screenshot. 0.4 is fairly high but not drastically so. 

The only other reading that is a bit strange is the MAF value of 10.26, but the engine was stone cold then so that may explain it. The 6.6 with a slightly warmer engine looks to be what I would expect.  

OK - many thanks! It seems that the DPF doesn't work the way I thought it would - given that it is a filter, I imagined it wouldn't allow any soot particles to get through.

It mustn't work as a true absolute filter.