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Mitsubishi 2.4L 4N15 DPF troubles

Oh dear! DPF SYSTEM SERVICE REQUIRED, WHY?


The most common causes of this issue:

  • Turbo intercooler and boost system leaks.

  • Oil dilution (Diesel in the oil)

  • Malfunctioning sensors.

  • Running rich.

  • Faulty diesel particulate filter.


So, we have a lot to unpack here!


Turbo intercooler and boost system leaks


Image: split intercooler hose.


Boost charge air line leaks can lead to DPF problems, and here’s whats going on:


1. Turbo Boost Pressure Loss:

The boost charge air lines carry pressurised air from the turbo to the engine. If these lines spring a leak, the engine isn’t getting as much air as it needs. Since the engine relies on the right air-fuel mix to run properly, a boost leak throws that balance off.


2. (Too Much Fuel, Not Enough Air):

When there’s less air coming through due to a leak, the engine burns more fuel than it should (a rich fuel mixture). This causes incomplete combustion, producing more soot and incorrectly burnt fuel.


3. Soot Overload in the DPF:

The extra soot created from poor combustion has to go somewhere – and much of it gets trapped in the DPF. Over time, the DPF gets overloaded with soot, making it harder for the system to burn it off during normal driving.


4. Frequent or Failed DPF Regenerations:

The DPF is designed to clean itself by burning off the trapped soot, a process called regeneration. However, if the engine is pumping out more soot than the DPF can handle (because of the boost leak), the filter might not regenerate properly. This can cause DPF warning lights or even a fully blocked DPF that may need to be cleaned or replaced.


5. Limp Mode Risk:

If the DPF gets too clogged with soot, the vehicle may go into limp home mode to protect the engine. When this happens, your power is limited until the problem is fixed and the fault has been cleared.


Signs of a Boost Leak:

  • Whistling or Hissing Sound: You might hear a hissing noise when the turbo kicks in, which could mean a leak.

  • Loss of Power: The car may feel sluggish, especially when trying to accelerate, because it’s not getting enough turbo boost.

  • Black Smoke: Dark smoke coming from the exhaust can be a sign that too much fuel is being burnt without enough air..

  • Poor Fuel Economy You might notice you’re burning through more fuel than usual.

  • Leaking intercooler, intercooler hoses or intercooler seals, seen as an oily black residue forming at the seal flange joints.


What Can You Do?

There are aftermarket intercooler hoses and intercooler seals available, we have a stock of these at the shop for sale. Or see a Mitsubishi dealer for replacement. Easy DIY fitment, or see your trusted mechanic.


Oil dilution (Diesel in the oil)


The rising oil level in Mitsubishi Triton 4N15 engines and Pajero Sports is something many owners have come across, and it's usually caused by diesel fuel getting into the engine oil. This can happen when extra fuel finds its way into the oil system, causing the oil level to increase. Consequently, thinner oil can cause excessive blow-by past the piston rings, heavily contaminating the DPF.


Check the engine oil dipstick! You'll see an X marked above the fill line. This marks the oil over diluted level.


Here are some common reasons why this might happen:


1. DPF Regeneration:

During DPF regeneration, extra fuel is injected to burn off the soot in the filter. If the regeneration doesn’t finish properly, like if you’re only driving short trips or turn the engine off while it's regenerating, some of that unburnt fuel can end up in the oil, making the oil level rise.


2. Lots of Short Drives:

If you're mainly doing short trips, the engine might not get hot enough to complete the DPF regeneration process. As a result, unburnt fuel can make its way into the oil and cause the level to go up.


3. Fuel Injector Problems:

If a fuel injector is faulty, it can allow fuel to leak into the cylinder, and from there it can mix with the oil, raising the oil level.


4. Issues with the EGR (Exhaust Gas Recirculation) System:

If the EGR system isn’t working properly, the engine might not burn the fuel efficiently, and excess fuel could end up mixing with the oil.


What You Can Do About It:

  • Check Your Oil Levels Regularly: Make it a habit to check your oil level to ensure it’s not getting too high.


  • Let the DPF Regeneration Finish: Every now and then, take your vehicle for a longer drive at highway speeds so the DPF can fully regenerate.


  • More Frequent Oil Changes: If this happens a lot, you might want to change the oil more often to keep it clean and avoid any damage.


Note: When the oil has been changed, the oil dilution meter will need to be reset correctly via scan tool, or through dash control settings.


Malfunctioning sensors and running rich.


3 common sensor issues

  • Mass air flow sensor (MAF)

  • Diesel particulate pressure sensor

  • Exhaust gas temperature sensors (EGT)

  • Battery faulty or loose connections


Image: MAF sensor


Image: MAF sensor elements


Image: MAF sensor elements


These vehicles are very sensitive to MAF sensor readings. If they become soiled or damaged, this will cause your vehicle all sorts of running issues, mostly running rich.

The DPF pressure sensor need to operate correctly to calculate the amount of particulate soot loading, to correctly achieve regeneration burns. We have seen these read faulty. These are located next to the DPF.


The EGT sensors also work in harmony with your engine to ensure safe running and work together with regeneration burn calculations. These are located with the DPF filter.


Another point to note would be your electrical system. As we have seen, loose battery terminals or a dud battery may wreak havoc on sensors and the ECM not operating correctly from incorrect voltages. Consequently, incorrect running and DPF soot loading.


Faulty DPF


Image: Faulty Pajero DPF


Over time, with excessive regeneration burns, poor fuel, poor running, excessive additives, poor vehicle operation and maintenance, DPF filters can fail, adding more insult to injury.


A replacement DPF will cost you heavily in time and money. The best approach is always prevention. Prevention in most cases, does not mean just "delete" these from your vehicle prematurely. Unless in your case, you have a dedicated offroad or farm vehicle, and can legally do so.



Summary


Based on our extensive experience, we’ve identified common issues with vehicles like the Pajero Sport, especially related to DPF problems. The most frequent causes include turbo intercooler and boost system leaks, oil dilution (diesel in the oil), malfunctioning sensors, running rich, and faulty diesel particulate filters. If you encounter any of these issues, we recommend getting professional help to avoid further complications.


I hope this information has been helpful for you legends out there with Tritons or Pajero sports. It’s been personally drawn from our experience at the shop with these vehicles, and having owned an MR Triton myself. This knowledge may transfer to similar vehicles. However, if you're stuck and need professional assistance, come and see us, or your local trusted independent mechanic.


Maia



Disclaimer:

The information provided in this blog is based on our experience with common DPF system issues in vehicles like the Pajero Sport and Triton. It is intended for general informational purposes only and should not be considered as professional advice for your specific vehicle. While we strive to offer accurate insights, we recommend consulting with a professional for any specific problems you may encounter. Vehicle systems can be complex, and proper diagnosis and repair by a qualified technician are essential to avoid further complications.






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