Technical Smokey Joe!!

[Paulk1979]

Hi, recently acquired a 58 plate 1.3 multijet doblo, and while it's great for getting three kids and three dogs in, it's let down by one very annoying fault. Dreaded dpf light!!

I really don't get it. I can drive for an hour at around 50-60 and then start it for my return journey and the light is on. Or it will just come on on a long journey.

When the light is on, it smokes like nothing else, choking and gassing out everyone in the vicinity with evil scowls from passer bys and anyone unlucky enough to have to breathe the filth in.

I've had the dpf cleaned out and an oil change done but this is still happening and driving me crazy, any suggestions anyone?

Paul

 

[Goudrons]

DPF's traps the soot produced by the engine, then as they fill with soot it regenerates.

This regeneration is a bit misleading, what actually happens is it ignites the thick particules of soot and burns it further so it becomes finer ash particules.
This reduces it's mass in the filter.
Eventually the filter will become full of ash and need replacing/cleaning.

To do this regeneration, it will inject extra fuel with a second injection of fuel late in the cycle (post injection) that passes through and is ignited in the exhaust by mixing with hot oxygen (raw air from the compression cycle) to raise the exhaust temps above 600 C.

This regen cycle can cause a certain amount of smoke from the exhaust, but it shouldn't cause anything like you describe.

Trouble is if it's not igniting this extra fuel, it washes past the piston rings and dilutes the engine oil, often to catastrophic levels.
Those that regularly check their engine oil level will notice it raise, those that don't usually notice the engine screaming away uncontrollably until it goes bang as a diesel will happily run on it's own engine oil if it finds it's way into combustion.

As you can imagine, the process is quite complicated and many things can happen to cause it to fail.

Owners tend to start/blame the filter it's self, but injector issues (leaking/injecting too much fuel), exhaust/manifold leaks (leaking hot oxygen out of the exhaust) and failed EGR operation (staving the engine/exhaust of oxygen) can also cause the process to screw up.

Modern diesels are very hard to diy these days, I would suggest finding a diesel specialist, a little spent on diagnosis can save you a lot of money in the long run, swapping parts in hope can be very expensive on a modern diesel.