DPF defeat by removing insides.

TheBoyConor

I was wondering about DPF defeat strategies. In my case I have the opportunity to take on a 151 1.6TDI passat for a song due to crash damage.
Is it the case for most DPF control systems that there are exhaust gas pressure sensors pre-and post DPF and that a regen cycle is triggered when the difference in reported pressure exceeds a threshold value? Is that the only egen instigator or is there a periodic cycle also triggered based on certain intervals of engine run-time possibly factoring in the nature of the engine's duty cycle/driving style over a preceding period of time.


I have seen some basic defeats that involve removing the exhaust pipe and then repeatedly hammering a length of pipe or bar up through the filter to disintegrate the filter matrix and effectively make it straight through. More complicated defeats involve cutting open the filter case and physically cutting out the inner parts.


If the innards of the DPF were removed so that there was no longer any significant pressure difference across the now empty DPF can, would the regen cycles no longer be activated by the ECU? Or would an excessively low pressure or consistently low pressure trigger a fault and limp mode.

If that is the case could the DPF regen cycle be defeated if the sensors were replaced by suitably fabricated electronics that mimmicked the signal of pressure that was below the regen trigger threshold? Is there any plug in sensor emulators that mimic what the "proper" sensor feedback ought to be so that a straight pipe may be used?

Waterson

There are some unscrupulous businesses who will do exactly what you describe: remove the blocked innards and effectively recode the engine management to ignore the DPF pressure sensor feedbacks. If you were to remove the filter element and not do this, the ECU would recognise a plausibility fault in the feedback from exhaust pressure (the ECU logic is written that it must see some degree of pressure differential between pre and post pressure sensors.
There are also more reputable businesses who will take a blocked DPF, ultrasonically clean it and provide pre and post cleaning flow test results to confirm the work. Depending on labour involved in removing a DPF, ( a couple of hours on a transversely mounted Audi engine) this could be a cheaper option.

TheBoyConor

I imagined that would be the case.

I'm not going to get into ultrasonic cleaning and testing etc. I want a cheap and cheerful fix.

To avoid having to install spurious software I am wondering is there any "dummy" sensors that can be plugged into the wiring harness instead of the real ones that spoof the ECU with a signal that would reflect a normal condition.

Basically regardless of the actual status of the DPF, they would just continuously tell the ECU what it wants to hear so that no faults or EMLs are triggered.

Another low tech idea I came up with is this - if the ECU is expecting pressure gradient to always be above a certain threshold, could the filter be gutted to a more limited extent to produce that value? That is, instead of smashing out all of the filter element, perhaps driving a pipe through it in one or two places might give the desired pressure gradient.

Pkiernan

TheBoyConor wrote: »

I imagined that would be the case.

To avoid having to install spurious software I am wondering is there any "dummy" sensors that can be plugged into the wiring harness instead of the real ones that will feed back the expected data.

Basically regardless of the actual status of the DPF, they would just continuously tell the ECU what it wants to hear so that no faults or EMLs are triggered.

Why are you looking to circumvent pollution controls on a dirty diesel car?

Why not do the right thing?

The sooner they make this an NCT fail the better.

TheBoyConor

Because it is too expensive and this is a car I can get for buttons money and I am not prepared to spend thousands on a dealers or a DPF. I want a quick fix that will get the car driving, NCT passible and more importantly, saleable.

tphase

I know someone who drilled a hole through a blocked dpf, didn't remap it or change sensors, car is running ok apart from excessive smoke. Doubt it will pass the next NCT though

He welded a steel bar to a flat wood bit to make it long enough to go through - very messy job, lots of dust (probably carcinogenic). Not worth it, IMHO

punisher5112

Get it cleaned, it's actually not as expensive as you may think op, get it done while fixing up the car.....

Are you going to be mentioning the crash and repair to the new owner?

Belfast

Do you know what caused the problem in the DPF? The DPF may be a symptom of the a problem in the engine.

The Truth About Diesel Particulate Filter Problems (DPF Problems) | Auto Expert John Cadogan



But DPF blockage is a symptom, not a problem. Like a headache is a symptom, and drinking 14 bottles of tequila last night is the problem. Replacing the DPF usually doesn’t cure the problem - in fact, it could mean you’ll be back for another replacement in a few weeks-to-months if they don’t actually cure the problem.

The problem could be as simple as: you didn’t go for regular highway drives you were supposed to. City driving is generally inadequate to allow a filter-regenerating burn.

But many people who experience DPF problems are actually doing more than enough requisite highway driving - so it’s often not that. It could be a problem with the inlet air plumbing - lots of DPFs fail this way. See, a modern diesel is turbocharged, and that means the inlet air plumbing is pressurised between the turbo and the engine inlet. And there’s a lot of plumbing: hoses connect the turbo outlet to the intercooler inlet and then there’s a dirty big plastic elephant trunk thing in the case of Subaru - so there’s a lot of potential for inlet air leaks. The problem here is: the mass air flow sensor. The MAF sensor measures the mass of air going into the engine, in real time. That’s important because the computer uses that information to determine how much fuel to inject.

Only two things go into your engine - air and fuel. And the ratio of the two needs to be bang-on. Measuring the mass of air makes sense because it self-corrects for pressure and density and the generally squishy properties of air. The mass is all that matters.

But if there’s a leak in the inlet air, downstream of the MAF sensor, because a hose gets a tiny crack in it over time, some of that air that the MAF sensor measures is not actually going into the engine.

And that means the engine will be over-fuelling, continuously, under boost, and that’s going to produce a whole bunch of additional carbon that will be like opening the Book of Revelation inside your DPF. That’s bad. Four tiny horsemen in there, wreaking carbon-based, end times havoc.

Induction leaks are real killers of DPFs - so if you are buying a used diesel car or SUV, it could be an entirely prudent idea to replace all the induction plumbing hoses as a pre-emptive strike against early DPF failure. Especially on the wrong side of 50-60,000km.

Over-fuelling is sometimes also caused by leaky fuel injectors - so I’d be getting a diesel specialist involved in the proposed purchase of any used diesel with a DPF - and not handing over the cash until there’s a clean bill of health from an expert.

It’s also very bad to use the wrong engine oil. DPFs require a special low-ash oil - and there’s more than one grade of that, so make sure you get the oil selection exactly right for your car. Another way to kill your DPF with oil is via a leaky turbo oil seal. So I would absolutely not be letting those service intervals slide.

Sticky EGR valves are another DPF killer - pumping excess crankcase vapour into the exhaust. Faulty glow-plugs - also DPF-deadly - because they cause the engine to run too rich on start-up.

And then there’s the differential pressure sensor across the DPF - all that does is measure the pressure drop across the filter. That tells the control computer there’s enough soot built up to trigger a regeneration.

But if the plumbing to that pressure sensor gets clogged, the computer presumes no regeneration is necessary - even if the filter is in fact choking to death.

I hope you can see that this is a complex system that, at times, to me, seems almost doomed to fail. And the failure is hardly ever intrinsically due to some deficiency in the DPF itself. In general, just replacing the DPF will lead to just replacing the DPF again - in a few weeks to months. And nobody wants that - even though plenty of people do it. Often the dealership will be ill-equipped to solve your DPF problem. They are generally fairly crap at diagnosis

Were I you, on the dreaded DPF merry-go-round - I would look for an independent diesel specialist with runs on the board with DPF diagnosis. It’s not rocket science ‘down there’ - but it is a bit complex for your average dealership Muppets who think taking orders from a scan tool is the same thing as being a mechanic.

My DPF light has come on: What do I do? | Auto Expert John Cadogan