Diesel particulate Filter trouble

Following another successful and involving DPF training course at ADS I promised the delegates I would do a write up and case study of the BMW 325d we had in the workshop for diagnostics and repair.

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The said vehicle we were presented with was an E92 BMW 325d 2007 which was presented into our workshop on Wednesday by what can only be described as a very nervous owner who has been given such a huge and varying array of advice and trawling the internet !! We all know where that can lead.
I invited the customer into the workshop for a spot of counselling and guidance and quickly convinced the gentleman that we were the company to trust in swiftly diagnosing and repairing his issue related to DPF and managed to also borrow his car for use with the training course in exchange for a free diagnostic health assessment of the DPF system.

I spent at least 30 minutes with the customer over a coffee on fri night to build up a profile of not only how the vehicle is driven but what fuel he uses, extensive service history, average journey time and distance to really build up a very detailed and accurate profile which is the key to unlocking successful DPF diagnosis.
I promise all my readers that if you follow these simple steps then diagnosing DPF systems will become very efficient and a huge profitable asset in your diagnostic arsenal.
There are no magic wands or silver bullets when effectively diagnosing DPF systems only rigorous and strict procedure which involve, customer profiling and gathering key drivability and service information, and correct interpretation of data which arguably is the corner stone of all solid diagnostic protocols.
It amazed me to the variety of advice he had been given and I must admit the best advice he was given was by his regular service garage he had used for ages who turned to him and said “this is way beyond us I suggest you take it to a specialist “

Awesome advice, bravo chaps, it’s both refreshing and miles easier getting first bite at the cherry before anyone else gets a go at contaminating the crime scene  and wasting hundreds and in some cases thousands of pounds needlessly.

This honest and upfront approach gained respect from myself and the customer.

I say DPF is my favourite subject because it’s challenging and almost infinitely variable in its degree of complexity due to the many factors involved in correct and nominal function.
It’s paramount before diagnosing and tackling any problem to have a firm grasp on how the systems work and fully understanding all the ingredients in the mix.

So here are the basic rules.

For successful and continued passive regeneration to take place the key factor is optimum exhaust gas temperature (EGT) of around 250 degrees for close/thermo coupled systems.

This is often achieved on highway driving at approx 60 MPH where the platinum coating converts carbon molecules into carbon dioxide naturally and without producing ash. Sadly this sort if driving is not always achieved and the DPF filter acts as a trap and the silicone carbide substrate acts like a spiders web causing any passing carbon molecules or particulate matter to stick for safe keeping protecting the air we breathe. Great !!

A simple and pre determined pressure value programed into the DDE module which can vary from system to system but in this case normally a sustained reading of 500 m/b whilst driving or 3.8 v from the sensor would indicate a blockage which would normally trigger active regeneration to take
place.
Now this is where it gets interesting and often leads to incorrect diagnosis and repair procedures in majority of cases destined to fail carrying a heavy burden in the shape of an unnecessary hefty repair bill.

Again if we really simplify active/forced regeneration it’s just a targeted increase in EGT designed to oxidise particulate matter trapped in the substrate into carbon dioxide causing a slow and inevitable build-up of ash and gradual breakdown in the precious metal coating of platinum which is absolutely vital in the passive regeneration phase.
So it’s very important we fully understand and separate both passive and active regen phase and I will explain and go into detail later on.
We initially investigated DTC’s in the DDE 6 control module which presented fault codes relating to glow plug circuit 2,3,5,6 and DPF system.
See pic 1.

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It’s worth adding at this stage the vehicle has been subject to long life servicing via CBS command or
I will say lack of servicing.
See picture.

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Glow plugs play a huge and vital role in the Active/forced regeneration phase and if faults are stored in the DDE relating to glow plugs then active regen temperatures cannot be achieved !
Thus meaning unless the vehicle is driven on the highway at optimum passive regen temps then all attempts to actively regeneration will ultimately fail !!
The majority of thermo coupled systems require a number of actions to be taken by the DDE control unit to achieve active regeneration temperatures on 650 degrees c.
1. Extra fuel at 35 degrees after TDC
2. EGR shut down
3. Swirl flap operation
4. Glow plugs fired
5. Increase of turbo boost pressure
All of which allow a targeted and carefully controlled increase of EGT or as we call it, active
regeneration.
Now if you understand what it takes for these conditions to be met you will also appreciate that any malfunction on the above components would cause a drop in EGT. So any DTC’s relating to any of the above would prevent the self cleaning process of the DPF causing quick and inevitable blockage during limited drive cycles.
This is the very reason we put huge effort into cleaning and choosing the correct flush treatment in order to maintain a clean EGR and inlet system.

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The same can be said of clean oil into a clean engine which the BG 109 product excels at maintaining.
On this vehicle I quoted the customer for a thorough engine/oil flush, EGR removed cleaned, BG Induction system clean and good service including replacing the faulty glow plugs.
Once I had carried out the work I was in apposition to accurately evaluate the severity of the
blockage.

An initial reading was taken at idle of 58m/b, and another reading at wide open throttle which produced a reading of 520m/b. These reading were way too high but by no means the highest I’ve seen.

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I decided to clean the DPF in situ by removing the Lambda sensor and applying a chemical cleaning solution using compressed air via a lance covering the face of the DPF and following off with a rinse solution.
I then ran the vehicle after replacing the lambda sensor at 1500 rpm for exactly 30 mins until all the dog vomit and steam from the exhaust had dissipated. I noted the pressure reading taken at 1500rpm dropped to 135 m/b.

DPF pressure reading immediately post clean @ 1500rpm

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Once completed a quick blip of the throttle would show an acceptable peak reading of 150 m/b ! Confident I had identified the initial cause of Blockage and carried out a sound repair including flush treatment I was now in a position to qualify my repair.

Using Autologic, I Firstly a reset DPF Ash adaptation and test drove the vehicle whilst monitoring the EGT at a steady speed and noted pressure build up to ensure natural passive regeneration was able to take place.
See results.

After and extensive test drive to confirm proper DPF functionality The vehicle was fully reassembled steam cleaned under the bonnet and fully valeted and shall be presented back to the customer later today.

For training courses and further info click www.autoinform .co.uk

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