DPF differential pressures. What is reasonable for a 2.0HDi?

[Wolds407]

Does anybody know how to judge the pressure differences across a Diesel Particulate Filter? I appreciate the cars computers will try to initiate regenerations to keep the DPF working as best as it can, but I was wondering if anybody had any sort of chart that would indicate limits or zones so I could plot the differential pressures I get during diagnostics and see if my DPF is healthy or ailing...

A long time ago I did find the chart attached but, judging by the flow rates, it must be for some kind of huge engine. I also found a set of maximum figures for a BMW but I would think limits are specific to each engine. I'd like to find some figures for my 2.0HDi so I can keep an eye on the DPF condition each time I service it.

When I run diagnostics on my 2.0HDi I record the differential pressures at a range of engine speeds. When I plot these they're well below the maximum figures I found for the BMW engine but are they respectable? I suppose no warnings on the dashboard suggests they're not bad and I'm concerning myself quite unnecessarily, but my cunning plan is to plot figures at each service so I can see if there's been any deterioration and hopefully nip any issues in the bud.

[GiveMeABreak]

The differential pressure sensors on this engine operate within these parameters:

Key

"C": Sensor output voltage In volts.
"D": Pressure in Bars.

They only operate from 0.5 to 5 Volts:

Voltage supplied for a differential pressure of 0 bar: + 0.5 Volts (engine off).
Voltage supplied for a differential pressure of 0.9 bar: + 4.1 Volts (particle filter clogged).

You also need to be aware that the differential pressure sensors are not solely used to determine the state of the DPF. The amount of particle filter additive that is injected into the fuel system and ultimately the actual particle filter is also recorded in weight (grammes). At some point, according to a pre-determined weight, the engine ECU will flag a warning as to when it estimates the particle filter has reached end of life and needs replacing (or cleaning) based on the amount of additive injected. There are components like Cerine in the additive, engine deposits and ash that cannot be burned off, so these all play a factor in the calculations.

[Wolds407]

Thanks Marc. That adds to my understanding.

The 900mbar for a clogged filter seems a high threshold (certainly compared to the BMW figures) but, as you say, there are plenty of other things being measured in parallel and it perhaps wouldn't be differential pressure at that level by itself that would tip it over the edge to light an undesirable light.

I do look at all of the figures to try to understand which way things are going. I'm not entirely sure what I would do if I saw change for the worse in the DPF. I keep a close eye on the fuelling and additive parameters each time I do a service but assuming all is well there, perhaps I'd try a few tankfuls of premium fuel or one of those special snake oils or something to see if any real improvement can be made...

Expensive and irritating DPF problems that I have read about put me off diesels to some extent but I like the economy and pulling power... I like to try and make things last. My 406 had the original DPF working all of its 20 years so I'm hoping the 407 will, properly looked after, keep going without problems too.

I'll look at the pressures again next service and update the chart out of curiosity.

Any other data out there that can be offered here would be appreciated

[GiveMeABreak]

I always use a premium diesel every 3-4 tank fills. They do have advanced properties in to help the fuel system. Used regularly, they omit the need for any other fuel system cleaners. I would not put anything else into the tank either to be honest.

Regeneration will occur naturally of course if the exhaust temperature reaches 550 °C, or at 450 °C with assisted regeneration when necessary. Obviously regeneration cycles and the mileage in between each, will depend on the journey type. Smaller journeys with stop and start traffic are the worst, and these will cause regeneration to occur more frequently.

DPFs are designed to last around 120k miles (depending on model year and type fitted) but some have seen longer mileage out of these. They can be cleaned to remove some of the ash these days in situ for a reasonable price, but the prices are a lot less for replacements than we saw 20 years ago. They should be seen as an operating cost for the benefit of having a diesel and for reducing the particulate matter by 99.9% in the case of the systems fitted by PSA. That and the addition on later engines of the Selective Catalytic Reduction system make these far more environmentally friendly than a lot of the eco warriors would have you believe....

I've never had any issues with any of the DPF systems on any of my cars to date. Just respect the maintenance periods and use good quality engine oils that are to PSA standards (which are often higher than the minimum standards).

[Wolds407]

I always used premium but now I'm giving regular a go for a while - partly looking after the pennies, partly looking to see if it actually makes a difference. Time will tell. I'm with you on the fuel tank being for fuel. Only once was I coerced to put a diesel treatment in - to pass an MoT. To be frank the tester was abusing his equipment (unwittingly or perhaps for extortion) by testing the car cold, without purging and not following the great big instructions on the screen in front of him when revving... So, he got a visit from DVSA although I won't be going back personally to find out if it did any good!

I'm sure well maintained diesel cars driven sensibly contribute relatively little to our pollution problems. Interfering with the good that has been done by the engineers is a step backwards - that's a little dig at the EGR blankers and their ilk

The 406 2.2HDi was a 2001, so quite early for a DPF. It did well over 150k, the DPF checks were fine and it always sailed through emissions tests. The additive dosing system failed about 5 years before rust finally took her from within but, by (carefully) adding by hand a shot of the genuine additive with each fill up, that side of it all kept working very well. The right oil too - definitely makes a difference