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The great DPF myth

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  • The great DPF myth

    having spent a lot of time reading and monitoring the Fortuna I believe I have worked out what is really happening with Toyota’s 2.8
    The hardest thing is working out which DPF protocol regen happens. There is several different ways regen is accomplished.

    - passive regen that can include oxygen or nitrogen dioxide (produced by cat) to work as a catalyst with soot.
    - another passive way is getting the DPF up to 600 deg by extended highway driving. I believe the cat which is situated just before DPF helps greatly with this, there could also be a catalyst thing going on too.
    - active regen by dumping extra fuel into exhaust to raise temps and burn soot into ash. This is triggered by the DPF sensor once it reaches a certain value. I am guessing approximately 2.5v here.
    - forced regen where active regen is forced by a scan tool.
    - Isuzu light trucks would active regen every 300km no matter what other truck manufacturers just replace or clean when full.

    what I have noticed with my tuna and it’s got over 80000km on it is this
    - it hardly ever does a active regen by using 5th injector, coming off Fraser Island it did and it was pretty harsh. But Fraser is 4wd low speed and lots of load which means high soot output and no condition for passive regen.
    - most of my driving is highway for 20 mins up to an hour most days every week. After monitoring the DPF sensor it didn’t go over 2v under full load and sat mainly around 1v under all other driving conditions. No active regen even after well over 500kms. The voltage reading tells me DPF is clean.
    - with a scanguage 2 I have monitored both exhaust gas temps and DPF temps. Outcome of this is around town and highway exhaust temps sit around 250 up to 400 deg tops depending on load.
    - what is very interesting is the DPF temps around town compared to highway driving. Around town its 400 to around 500 deg tops. Highway driving it’s a minimum of 580 up to about 610 deg which is the temps needed to burn soot.
    - so under extended highway driving vehicle is pretty much always in passive regen mode this means a clean DPF.
    - around town, short trips on highway, 4wd, heavy loads passive regen will not happen. Vehicle will rely on active regen after filter is getting pretty sooted up, which is harder to get clean. This can cause as I have read on here “regen anxiety” and will get worse as DPF gets harder to clean.

    - solution for the long term will be difficult for these vehicles. The local Toyota dealer does 1 to 3 DPF replacement every week. Imagine the expense when they are out of warranty. Toyota really should have a petrol option available and salespeople should inform customers about driving conditions needed for DPF health.

    hope this helps shed some light on a subject that has lots of myths and is hard to work out cause Toyota engineers don’t release that type of info.

    Cheers, Spook

  • #2
    Just found the scangauge 2 code for DPF pressure sensor, DaveC put it up a while ago. This code is the digital data from the analog voltage I mentioned above when I referred to DPF sensor sitting around 1v and 2v under full load.
    so thanks DaveC👍

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    • #3
      I agree with with youre saying , but i suspect the 5th injector works more often than we think. Would adding an LED across the 5th confirm the active regens ? I suspect the 5th is partially opened ( by a PWM signal ) to achieve partial burns where full burns are not required . its only my theory at this stage.
      i think if the 5th blocks up then active regens cannot happen , leading to a DPF failure.
      2016 GX , in White

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      • #4
        Hi Guys,

        My observations (using SG2) are a little different. I've *never* seen this so-called passive regen condition, i.e. where the EGT naturally reaches 600+ degrees. My EGT is typically between 300-450, except when an active regen occurs, which is approximately every 300klms when the DPF% (as per my guide) reaches 100%, then the temps jump to 600-700deg while the burn takes place, and quickly drop back to 400ish afterwards. I assume this active regen is initiated by operation of the 5th injector, but I can't be sure, perhaps the ECU can do other tricks to raise the EGT temp. In any case, it is a very deliberate action by the ECU. Also, it may be the case that the 5th injector is only required to kick things off, then once the temp is right, the burn continues on its own.

        My friend with a 2.8 prado has had the same experience as me. He has also mentioned reports of DPF replacements documented on pradopoint (at as low as 30,000ks) . I'd love to know the official diagnosis/cause of these failures from Toyota, but I'm not holding my breath.

        I follow this topic with interest as I want to understand how it works and what failure cases may exist, and how I might prevent or recover from them in the middle of nowhere! However, I must also stress that I've personally *never* had any problem with my DPF system (at 30,000ks now), nor do I advocate removing the DPF as it is illegal and is a human health issue.

        Dave

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        • #5
          If the fifth injector blocks from soot you are in trouble hey!
          It possibly could work more for shorter periods but I believe will only trigger on higher DPF sensor values. (Just my opinion and could be wrong)
          driving conditions will determine how often this will occur so every one will be different.

          But certainly worth investigating cause often when I think I have something worked out it goes sideways due to learning something new.
          But how good would it be if people on this site really understood what’s happening with their DPF.


          a mini hand held scope would be best for me anyhow, the LED would be connected in parallel but considering the injector pulls about 1.5 amps (8.7 ohms resistance across injector) and the back EMF I would expect to be similar to petrol injector so looking at about 70v there as solenoid winding collapses. So if you can protect it from that then it will work. It has a constant 14v supply and earth switched. If you can work out the wiring of LED around that would be a cool project anyone can fit on their car. The LED from positive wire to neg wire on injector would work, just need the correct resistor. Wiring it up any other way LED will be on all the time.

          ill put a little scope on it and monitor exhaust temps with any pulse width from it. I would expect exhaust temps to maintain a high value rather than the fluctuations you see on scangauge under load / RPM changes.

          i love doing this stuff 👍

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          • #6
            we also own a new MQ Triton , and they do a burn by increasing the fuel mix into each cylinder ,thereby increasing EGT temps. I dont know if that is the best way of doing it but it works , no smoke or failure issues on them to my knowledge , and that car cost us $22k less than the Tuna.
            2016 GX , in White

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            • #7
              Hi DaveC
              the exhaust temp is the same as you say but the Third temp gauge in the DPF is what I’m reading off scangauge. I got the code for it from a post whiteOne put up.
              So driving today I found that driving on highway the DPF temp climbed up to 200deg higher than the exhaust temp ever went.
              This I believe is the passive regen

              Comment


              • #8
                maybe there is a wide difference in meaning between the two terms , active and passive , and how they are achieved. I often see DPF temps of 500deg , so ive been calling that a passive , and when i see temps of 760 i call that an active???
                I have assumed ( maybe falsely ) that when i see the 500s it means the 5th injector is being opened by PWM and only a small amount is squirted in ??? i dunno.
                2016 GX , in White

                Comment


                • #9
                  This is active regen-
                  The Triton is same as with older technology where rather than a 5th injector putting fuel into the exhaust the actual cyl injector has a Post Post injection phase where upon active regen / forced active regen it sprays fuel after the combustion event (so second squirt of fuel after main injection). This raises exhaust temps and DPF temps to 600 - 800 deg to burn soot.

                  This is is passive regen -
                  DPF temps reach high temps (600 deg) through extended highway driving. The cat I believe will have a lot to do with this as they are hotter on the outlet than the inlet. Passive regen can also be a catalyst action through either oxygen (coating in DPF) or hydrogen dioxide (made from cat)
                  no fitfh injector or post post injection phase is used.




                  Comment


                  • #10
                    I found DPF temps of the 300 (cruising) to 500 (acceleration) range when driving around town.

                    DPF temps of 580 to 610 on highway. 200 deg hotter on average than exhaust temps ever were.

                    this indicates a passive regen due to exhaust temps never increased which would if active regen (5th injector) occurred.

                    i hope this is starting to make sense, so much easier to explain face to face with a vehicle / pico scope and whiteboard with whiteboard markers.
                    my writing skills are not the best when it comes to writing articles/ information.

                    maybe one day we can get together for a tuna weekend

                    Comment


                    • #11
                      I’ll keep monitoring the tuna to see how it operates under my driving conditions with the SG2 data. I’ll hook up the 5th injector to scope too.
                      DaveC can you share the driving conditions that your tuna normally operates please mate... like how much highway driving would you do between each regen?
                      Our vehicles appear to have different things going on with regen. Yours is obviously going in active regen mode with your exhaust temps and is great data to have especially with the driving conditions to match it.

                      cheers

                      Comment


                      • #12
                        I'm with DaveC on this one.

                        I have all 3 EGT on screen at any point in time, I've never seen passive regen.

                        I've only seen an active regen initiated and maintained by the 5th injector. I'm also monitoring fuel flow, this increases significantly when an active regen occurs.

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                        • #13
                          This is well written and worth a read.
                          http://blog.toyota.co.uk/toyota-dpf-...iculate-filter

                          cheers

                          Comment


                          • #14
                            Also good stuff
                            https://practicalmotoring.com.au/car...youre-offroad/

                            The hardest thing is trying to work out exactly what out Toyota’s are doing. It really seems by the input (thanks guys👍) that cars are responding differently and seeing we have the same vehicles it’s got to come down to driving conditions.

                            Here I am thinking these cars hardly ever go active regen and it’s not the case for other people.

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                            • #15
                              I got some pics of what I notice
                              ATF -trans temp
                              EGT -exhaust gas temperature
                              DPF -particulate filter temperature
                              DPP -particulate filter % (you guys have noticed a forced regen when this hits 100)

                              Pic 1 after car warms up EGT 240 deg, DPF 366,
                              DPP 18% blocked.

                              Pic 2 after bit of a drive but still actually around town (yeah this is weird) EGT 297 (didn’t go much higher than this on drive at all) DPF 632 deg (way above EGT) DPP drop to 12%

                              Could you guys do something similar and if someone could capture a regen that would be awesome.
                              I really appreciate everyone’s input to see what the hell this car does.
                              Cheers, Luke

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