Here we go Again
Here we go again everything is about the blasted STAR machine! Just go and pay someone with a STAR Machine to tell you what you already know! It's the biggest con ever just a money making scheme. I've yet to find a Merc Specialist with the STAR machine who will put his money where his STAR Machine is!
Any half decent fault code reader will help you because it will give a code the code which will tell you in which direction your problem is. No code reader tells you what the fault is for example if you if you unplug your cars MAP sensor any code reader will tell you there's no reading from the MAP sensor so when you go and look you will find the plug is off, this does not mean that the MAP sensor is faulty but it does tell you that the problem is in that direction go and investigate.
In your case you already know it the DPF.
How the DPF works is it catches soot in the filter component of it, then the pressure builds up as the exhaust gases can't escape because of the soot so the pressure sensor on the DPF will tell the ECU it’s time to regenerate which in layman’s terms means time to flush out the soot.
Your car will do this by itself you will notice a increase in fuel consumption for a little while because the EGR will close more fuel will be pumped into the cylinder more air will be pumped by the turbo increasing the working temperature of the exhaust from between 150-250 degrees Celsius (round town temp) to 650 degrees Celsius DPF flush out temp. This process is done automatically and you don’t need to pay anyone with a STAR computer to do it.
Now the Problem
If your car has been poorly serviced for example poor oil, poor fuel, irregular service intervals and just sheer neglect then the ECU will do its best to flush the DPF but with poor results, this will cause excessive Caking of the Filter so even at 650 degrees Celsius it won’t budge the soot. So your car will go into a cycle of flushing the DPF which will cause really poor fuel economy.
So what I suggest is a full engine service with a really good engine flush and really high quality oil which dislodges sludge from inside the engine. Then try using high quality fuel (after changing the fuel filter) replace the Oxygen sensor and if need be replace the DFP sensor so they can give an accurate reading to your cars ECU.
Then remove the DPF soak it in Thinner just any standard thinner from a motor factor make sure that the filter is totally submerged weigh it down if need be so that the filter gets soaked and leave it over night so it soaks well (Be Very Careful Thinner is Very Flammable)
The next day drain it out you will see the thinner will have gone black with the soot, Keep flushing it and till you think most of the soot has gone, then pressure wash it using a high pressure car washer then using a high pressure line blow air through it.
Once you are convinced it’s clean as you can get it, refit it to the car.
After I had done this to my car I could not believe the difference I didn’t even have to reset the fault codes they all went off and the car was driving smooth turbo cutting in and out MPG averaging 37 local and 55 on the motorway.
Star Machine MY **** just good regular maintenance and a bit of common sence.
Good Luck with yours