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2012 SH Manual Diesel
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Discussion Starter #1
Thought it’s about time to share my experience cleaning my own DPF.

Have been driving with the cleaned DPF for over 30,000 kms with no problems. I hadn’t had any DPF problems, but failing to find a cheap used DPF to trial, I figured mine had to be the test subject.

After scouring the Internet for information on DPF’s, types, potential problems, cleaning methods, and products, I found a Military study on engine damage caused by back pressure from a clogged DPF. It pointed the finger at ‘Ash’ plugs.

I spent a bit of time thinking about Ash, what is it, what is it used for etc. So, we know that ash can be incorporated into concrete as it has some binding properties like Portland cement. What is used to break down cement or concrete?

Look up an Alpha Hydroxy Acid (AHA), called Glycolic Acid. It’s made from Sugar Cane, and has the smallest structure of the AHA’s. It’s used in food production and also cosmetics. Since it has a small structure it has the ability to pass through the pores of skin (cosmetics), and concrete. However it is not highly corrosive like Sulphuric or Hydrochloric Acid so is less likely to attack the DPF or its precious metals.

Another chemical that could be used is a non-ionic surfactant. However my trial used Glycolic Acid.

I pulled the DPF off the car, taped up the holes the best I could (which was not great). Placed it in a bucket, and poured the Glycolic Acid into the rear end (backwards flush). I let it sit for half an hour, then flushed it with water. Once pretty much all the crap that was going to come out, had come out, I drained it and flowed air through it (back flush). When I put the DPF back on and took it for a drive, it so happened that I did a regen (which was good as it would have aided in clearing any residual moisture).

I was originally up to about 370 regens, and 40% Ash. After the clean I could feel the engine was a bit more responsive. No engine lights have come on, and no drive-ability issues either. I eventually reset the ECU with a Scantool. Now at about 40 regens, with 7% Ash.

Monitoring ODB data, the DPF is still doing passive regeneration. It will passively regen from 250-280 Deg C. I have a Dawes Valve and Needle Valve for boost control, and have it set, so I’m getting some passive regen at 60 in 3rd, 80 in 4th. Aiming for 100-110 in 5th as well, but finding the sweet spot with the boost control takes a bit of trialing, especially when adjusting for improved boost over factory but with good economy (6.0L/100).

Other things I’ve done in attempt to reduce potential DPF issues:
1) fuel catalyst for more complete burn
2) use an oil with a low NOACK value.
3) Catch Can
4) monitor ODB data to adjust boost settings, but also driving style
5) use premium diesel

The engine oil seems to be considered the larger contributor to ash build up, hence the C3 Spec. Possibly looking at HTHS and NOACK, especially if your engine sees high ambient temps can reduce the amount of oil ending up going through the engine and into the DPF. Also since C3 oils have less anti wear additives, looking for the highest quality base oil, might aid the longevity of the engine. As might a injector cleaner/lubricant, since new fuels have less sulphur.

If I was to do it again, I’d have a set up like a parts washer, where the cleaning fluid is filtered and cycled through the DPF continually. I’d consider using a surfactant first to clean out the soot, then the AHA for the Ash. I’d also have high volume (low pressure) air to blow through the DPF and do it in the heat of summer to aid moisture removal.

So if anyone is game enough, or desperate for a solution... this might be food for thought.
 

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2012 Forester 2.0D 6MT
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Very very interesting. Nice work.

Where did you find the glycolic acid, and what strength/dilution did you use?
 

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2014 Forester 6 M/T
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Hmmm interesting but how the passive regeneration can start at 250-280 Deg. C? Do you use some special fuel additive? I observed that passive regeneration starting at around 400 Deg. C.
 

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2010 Forester Diesel 6MT
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Hi Dogs,

great work and a great outcome. You've obviously put some research into the issue.

A few comments:
  • As the nitrogen oxides can form nitrous/nitric acids in water and this can go through the DPF I suspect the use of a weak acid may not be entirely necessary?
  • If the ash has vitrified on through a high temp event, it may not come off that easily, if at all.
  • Did you consider also perhaps using an ultrasonic probe in the bath to assist with the dissolution and/or ash delamination from the filter matrix? This may assist particularly in getting material out of the channel structures. I have used ultrasonic cleaning on materials including ceramics before, and generally ultrasonic cleaning only damages already damaged materials. To that end you'll probably want deionised water (at the very least for the rise) and a good ultrasonic-specific cleaner- I used to use Brulin 815 GD, designed for aerospace applications.
  • Engine oil is considered the largest contributor so long as the fuel isn't itself 'dirty'. The ash can be considered the leftover 'unburnable' contaminants (even though they may be oxidised) composed of inorganic chemicals. So remember by putting any additives in the fuel that contain non-organics (e.g. metallic catalyst components) you might reduce the soot load but you're actually adding to the ash load as these catalysts will be depositied (oxidesed or not) as ash.
  • The oil will mostly be being derated, I suspect, by oil dilution from diesel leakage past the rings from post-injection during regens. So if you can passively regen with any thing else- great. In the meantime, these Subaru engines actually seem quite mechanically robust- ours has (I think) ~260k km of DPF issues, abuse and unsuitable city driving and the engine mechanicals are fine. You just need to keep the oil changes up with the appropriate oil spec and change it early if it gets diluted.
  • The C3 spec is only mid-SAPS (Sulfated Ash, Phosphoruous and Sulfur). C4 and C1 are low-SAPS. It's interesting they stuck with mid-SAPS, I can only assume for the additives being required for engine longevity.
  • Could be worse, you could also have a Mazda 3 diesel like me which requires JASO DL-1 spec (similar I think to the C1 and C4 specs in terms of SAPS). Having said that, it's over 200k km without any issues at all (apart from 1 forced regen due to too much town driving). Interestingly too, the Mazda 3's a EURO4 spec vehicle.
 

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2012 SH Manual Diesel
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Discussion Starter #5
Very very interesting. Nice work.

Where did you find the glycolic acid, and what strength/dilution did you use?
Is was at a local Spare Parts store, sold as Concrete Remover. I just used the product as is. Since there's no guidance for this application, I just took a guess as a starting point. Unfortunately I only had one DPF to clean, so I wasn't able to try different combinations or products.

Most of what I could find being used was high pressure cleaning. One person tried hot water, another burning in some sort of furnace. Wynn's in the UK have a off car DPF cleaning solution, which I think is a tetrapotassium pyrophosphate. I was going to try it but couldnt get my hands on it. There is one other company with a similar product, but also couldnt get it either.

There are some fuel addititves, that also claim to have the precious metals in them, which are meant to end up in the DPF.
 

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Discussion Starter #6
Hmmm interesting but how the passive regeneration can start at 250-280 Deg. C? Do you use some special fuel additive? I observed that passive regeneration starting at around 400 Deg. C.
I'm just going off what I see in the ODB data, where I have seen the soot % drop at those temperatures.

I don't think it's just a case of high temps, it's also got to be at the right AFR. If there isn't enough excess O2, then not much passive Regen will occur, even at 400 Deg C. It's possibly another reason why the EGR closes during a DPF burn, to ensure higher O2 conc.

I have also watched the ODB data, where the DPF Temp was between 300-450 Deb C, and was just getting soot accumulation. This was whilst trialling different boost settings.

I have been using a fuel catalyst, which is said to lower the burn temp of the fuel to aid a better combustion. But I haven't had it in the tank for a few months (as my bottle pourer broke), and I still see the same temps for passive Regen.
 

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2012 SH Manual Diesel
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Discussion Starter #7
Hi Dogs,

great work and a great outcome. You've obviously put some research into the issue.

A few comments:
  • As the nitrogen oxides can form nitrous/nitric acids in water and this can go through the DPF I suspect the use of a weak acid may not be entirely necessary?
  • If the ash has vitrified on through a high temp event, it may not come off that easily, if at all.
  • Did you consider also perhaps using an ultrasonic probe in the bath to assist with the dissolution and/or ash delamination from the filter matrix? This may assist particularly in getting material out of the channel structures. I have used ultrasonic cleaning on materials including ceramics before, and generally ultrasonic cleaning only damages already damaged materials. To that end you'll probably want deionised water (at the very least for the rise) and a good ultrasonic-specific cleaner- I used to use Brulin 815 GD, designed for aerospace applications.
  • Engine oil is considered the largest contributor so long as the fuel isn't itself 'dirty'. The ash can be considered the leftover 'unburnable' contaminants (even though they may be oxidised) composed of inorganic chemicals. So remember by putting any additives in the fuel that contain non-organics (e.g. metallic catalyst components) you might reduce the soot load but you're actually adding to the ash load as these catalysts will be depositied (oxidesed or not) as ash.
  • The oil will mostly be being derated, I suspect, by oil dilution from diesel leakage past the rings from post-injection during regens. So if you can passively regen with any thing else- great. In the meantime, these Subaru engines actually seem quite mechanically robust- ours has (I think) ~260k km of DPF issues, abuse and unsuitable city driving and the engine mechanicals are fine. You just need to keep the oil changes up with the appropriate oil spec and change it early if it gets diluted.
  • The C3 spec is only mid-SAPS (Sulfated Ash, Phosphoruous and Sulfur). C4 and C1 are low-SAPS. It's interesting they stuck with mid-SAPS, I can only assume for the additives being required for engine longevity.
  • Could be worse, you could also have a Mazda 3 diesel like me which requires JASO DL-1 spec (similar I think to the C1 and C4 specs in terms of SAPS). Having said that, it's over 200k km without any issues at all (apart from 1 forced regen due to too much town driving). Interestingly too, the Mazda 3's a EURO4 spec vehicle.
Hmmm ultrasonics sounds interesting.

Well my trial was a very crude attempt, especially not having a great set up, and resources.

However, my thought was that if there was a suitable way to clean the DPF, owners could clean them prior to them failing or being completely clogged up. If A regular or precautionary maintenance was carried out whilst the ash content is low and less compacted, the cleaning efforts maybe more successful.

Another thought, is that Diesel Tuners, could tune for a balance of economy, power, and passive regeneration. If a certain speed and gear, along with a certain road condition, RPM, and driving style gave rise to passive Regen, then the driver knows what to do after any heavy acceleration, to avoid a DPF Burn.
 

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2010 Forester Diesel 6sp Manual
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Hi! Very interesting and useful information.
I had mine dpf removed long time ago since I tought 100km between regens in summer are way too often and something is wrong, but turns out it is normal... in winter I got ~500km between regens. the car had ~140k km and ~300 regens in total. I actually managed to find a cheap dpf (200eur), but have not installed it. not long ago I flushed it backwards with a garden hose and still got lots of black stuff coming out. My old removed DPF core is still in my garage and by blowing each individual cell you can see ash plugs come out of the other end.

as for Tuners - first thing would be adjusting EGR maps. When I still had my DPF i tried blocking EGR and that doubled distance between regens in summer, but will trigger CEL eventually. I now have my EGR set to close at 1800rpm (stock is 2600 or 2800 rpm), so it still works normal but when on speeds above 95 km/h in 6th EGR stays closed so that should help on highway soot accumulation. I am slowly testing things out before I replace my DPF.

as for AFR - I dont think there is much you can do, since diesel will use all the air it can suck and fuel is the element that regulates the power. Diesel is running lean all the time and when rich - black smoke is produced. Visible exhaust smoke is most noticeable when you are going on low revs and floor it and if you are in 3rd gear for instance it will take a second or two to take off and that will puff a smoke cloud in your DPF, so you would want to avoid sudden hard throttle dips in low revs. full throttle should not be a problem because stock fuel map is pretty lean on high air mass all across rev range. And very rich in low air mass, low rpm area, thats why you want to avoid throttle dips.
 

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Discussion Starter #9
Hi! Very interesting and useful information.
I had mine dpf removed long time ago since I tought 100km between regens in summer are way too often and something is wrong, but turns out it is normal... in winter I got ~500km between regens. the car had ~140k km and ~300 regens in total. I actually managed to find a cheap dpf (200eur), but have not installed it. not long ago I flushed it backwards with a garden hose and still got lots of black stuff coming out. My old removed DPF core is still in my garage and by blowing each individual cell you can see ash plugs come out of the other end.

as for Tuners - first thing would be adjusting EGR maps. When I still had my DPF i tried blocking EGR and that doubled distance between regens in summer, but will trigger CEL eventually. I now have my EGR set to close at 1800rpm (stock is 2600 or 2800 rpm), so it still works normal but when on speeds above 95 km/h in 6th EGR stays closed so that should help on highway soot accumulation. I am slowly testing things out before I replace my DPF.

as for AFR - I dont think there is much you can do, since diesel will use all the air it can suck and fuel is the element that regulates the power. Diesel is running lean all the time and when rich - black smoke is produced. Visible exhaust smoke is most noticeable when you are going on low revs and floor it and if you are in 3rd gear for instance it will take a second or two to take off and that will puff a smoke cloud in your DPF, so you would want to avoid sudden hard throttle dips in low revs. full throttle should not be a problem because stock fuel map is pretty lean on high air mass all across rev range. And very rich in low air mass, low rpm area, thats why you want to avoid throttle dips.

I tried to find a “Racing” DPF. I found a hint of one existing on a Euro website, but was unsuccessful in getting my hands on it. It’s either larger, or somehow less restrictive.

Another option I thought of, is trying to find a DPF off a larger capacity vehicle, so it might also provide less restriction, and therefore improve the power out of the motor. That idea kind of floated away, when I thought about Intercoolers....

Adjusting turbo actuation to some extent can, change the AFR or how cool or hot the burn is. Using a needle valve on the VNT actuator can adjust when the Turbo starts to produce boost, and how quickly it comes on. But this could also be programmed into a tune, or by using an electronic boost controller and solenoid (possibly coupled with either EGT, or AFR like with Innovate and GFB products).
 

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2014 Forester 6 M/T
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It looks that I have to clean my DPF after 5 years and 6 months. As you can see today I had active regen and it finished at 5% soot. Then I stopped car at the office. On the way home it dropped to 3% but then rapidly rises to 35% at only 7 km... Not sure if there is anything I can try other than DPF cleaning. I already tried additives for DPF, injector cleaner, ... but nothing helped. Any suggestions?

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If your engine running normally? Jumping from 3% to 35% soot seems unlikely. Maybe issue with the sensor?

Take it out for a nice motorway drive, 30min at least between 2500 and 3000rpm, 6th gear. Then see how it's doing.
 

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I take a ride on motorway as you suggested, hopefully I didn't get a fine because of speeding ;-) unfortunately till I get to motorway soot increased from 35% to 51% and even if temperature at DPF was arround 400-450 Celsius soot didn't drop much. And when I slow down in the city it start growing quite fast. Engine is running fine and I didn't notice any problem.

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Sorry to hear that. You can also try the same in 3rd or 4th gear. Basically minimal requirement is 60km/h, and at least 2000rpm for regen to work. And you have to sustain that for at least 10-15min.

I wouldn't go above 3000rpm because it becomes counter productive. Try it a few more times if you can and see if it helps.

Also, you might have an air leak, which would cause fast soot buildup. Inspect the intercooler hose and other intake components for any cracks.
 

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Also, you might have an air leak, which would cause fast soot buildup. Inspect the intercooler hose and other intake components for any cracks.
I second that. Happened to us. Also make sure the intake air hose clamps are tight.
 

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I tried to burn soot 2 more times on motorway and I looked at DPF temperature and I try to keep throttle as minimum as I can to keep DPF at 400 Celsius. Result wasn't great and soot burn out pretty slowly, after half an hour it lowered only by 10% and when I get back to the city after few km's I get rapid increase to the same value as before. At Monday I have appointment at Subaru service for checking DPF system and related stuff also for DPF diagnostic and cleaning. Will let you know the result. They can check the real airflow of DPF and back pressure. It will be interesting to see the result ;-)

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Did the DPF light on your dashboard turn on? Or maybe flashed intermittently? If you don't see the DPF light then your Subaru is doing a passive regen. If you see the light then you should not shut down the engine and go for a drive as described. If it's not convenient at that time you can shut it down and next time you turn it on, it will still be on and do the drive then. Don't shut down for too many times. Active regen will burn the DPF much harder than passive. But, if it's not successful then the DPF light will start to blink and at that time you don't have any choice but to go to the Subaru dealer so they can try to fix it by doing the active regen over the OBD2 connection.

Anyway good luck and let us know what you find out.
 

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Over the weekend things changed and I can't go to another city for DPF cleaning as I plan. It looks like some intake hose broke and I can clearly hear hissing sound from engine on increasing turbo boost. Tomorrow I going to my local dealer for checking and fixing this. Will see if it also fix the DPF issue.

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So just an update, short elbow hose from intercooler to engine, right side, has been broken and actually changed with new one. Will see how the DPF behavior change.

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Check my post #13. It's a very common failure. Should be better with the DPF if there are no air leaks.
 

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So it looks like fixing the broken pipe from intercooler didn't helped. I took a ride of 17km (mix of city & country roads) at speed 50-90km/h and result was soot increase from 11%-46%. Interesting thing is that DPF differential pressure almost didn't change. There was variation only 0-1kpa. It looks like DPF isn't that full and it didn't create a resistance at exhaust. So I don't understand why soot value increasing that fast... Any ideas? Obviously there should be something additional taken into account in the calculation formula for soot accumulation...


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