Buying Advice MT342

[cowboypride]

I'm about to pull the trigger on an MT342 but am concerned about the issues I've read about the DPF and limp mode.

Does the community agree these have been generally resolved?

 

[blitzn00]

Pull the trigger. Here's a quick DPF primer as these things are actually quite simple.

Diesel engines produce soot. The DPF traps the soot. To clean the DPF (called a regen - short for regeneration), the exhaust temp needs to get high enough to burn off the trapped soot (about 500-700 C dependent on oxygen concentration in the exhaust).

There are two types of DPF - Active and Passive. My LS342 has an active DPF - "Active" simply means a heat source (injected fuel in this case) is used to increase the exhaust temp to 500 C+ during regen. All active DPF's are also passive DPF's. Meaning the DPF can regen passively if the exhaust is hot enough for a long enough period during normal operation. That likely explains the different regen times people experience.

A backpressure sensor is used in active DPF systems to keep track of the soot loading. In smart systems the "rate of rise" of pressure over time is what is measured, and regens are pre-emptively initiated. If someone runs the machine in a way that allows for a passive regen(s), then there is almost always a time based regen coded into the ECU. So, for example, if no pressure based regen occurs in xx hrs, then a regen is initiated no matter what. That explains these 50 hour intervals you see reported.

I hope that helps and doesn't try to oversimplify or sound condescending.

 

[Roadworthy]

The explanation was clear and concise. I appreciate you taking the time to write it. I now better understand active and passive regeneration. Given your initial statement that diesel engines produce soot I suppose it's only a matter of time before the EPA decides ALL diesel engines shall have the particulate filters.

 

[blitzn00]

It's absolutely only a matter of time. Interestingly, the EU and the US use different methods. The EU limits particle count (engines can only produce xx number of particles - usually measured in particles per bhp -hr), but the EPA uses a gravimetric measurement (mass) so grams per brake horse power per hr, or g/bhp-hr.

Probably TMI .....

 

[Avenger]

Pull the trigger. Here's a quick DPF primer as these things are actually quite simple.

Diesel engines produce soot. The DPF traps the soot. To clean the DPF (called a regen - short for regeneration), the exhaust temp needs to get high enough to burn off the trapped soot (about 500-700 C dependent on oxygen concentration in the exhaust).

There are two types of DPF - Active and Passive. My LS342 has an active DPF - "Active" simply means a heat source (injected fuel in this case) is used to increase the exhaust temp to 500 C+ during regen. All active DPF's are also passive DPF's. Meaning the DPF can regen passively if the exhaust is hot enough for a long enough period during normal operation. That likely explains the different regen times people experience.

A backpressure sensor is used in active DPF systems to keep track of the soot loading. In smart systems the "rate of rise" of pressure over time is what is measured, and regens are pre-emptively initiated. If someone runs the machine in a way that allows for a passive regen(s), then there is almost always a time based regen coded into the ECU. So, for example, if no pressure based regen occurs in xx hrs, then a regen is initiated no matter what. That explains these 50 hour intervals you see reported.

I hope that helps and doesn't try to oversimplify or sound condescending.

That has got to be one of the best explanations of a DPF and regen I've seen. Good work! :thumbsup:

As to the OP, pull the trigger. If you spend all your time worrying about things that will not likely happen, you will never get anything done. Just, when your tractor starts to regen, unless you have a very real concern for starting a fire (tractor sitting in a dry wheat field for example), dont delay it. My tractor regens on a constant cycle, never had a single issue, and your MT342 has the same engine as mine. Just "idle" it at 1500 rpm.

 

[PCABE5]

There are four different diesel emissions, Oxides of Nitrogen (NOx), Oxides of sulfur (SOx), Particulate Matter (soot) and Hydrocarbons (in the form of unburned fuel). The DPF controls spot but also has to deal with some sulfur oxides due to some sulfur content in diesel fuel. The system on the LS engine is consists of a Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) and is sometimes referred to as a close coupled system.

Regeneration is the process where soot particles trapped by the DPF (Diesel Particulate Filter) are burned into ash (De-soot) and oxides of sulfur are burnt (De-SOx). This process involves a lot of different components as well as a program in the ECM triggered by the pressure differential sensor or by an internal counter.

First, there are three types of regeneration ‐ Passive, Active and Manual:

• Passive regeneration can occur when the engine is operating under load conditions that generate high enough exhaust temperatures to oxidize the soot particles trapped in the DPF.* Most will never see this as temperatures in the DPF will not get hot enough.

• Active regeneration occurs when the exhaust temperature is insufficient to achieve passive regeneration. Under certain conditions the ECM can automatically activate the fuel injectors to raise the exhaust temperature to achieve a successful regeneration. The ECM activates the injectors post‐combustion when the exhaust value would be open.

• Manual regeneration can be performed with a service software or button on the dash.

The ECM will start the regeneration process of the DPF if the soot load exceeds a calibrated value. The ECM determines the soot load of the DPF based on the voltage output of the pressure differential sensor. Or the ECM has an internal counter that runs anytime the engine is running. This counter is engine RPM and exhaust temperature dependent, so the more RPM the engine is turning, the faster the counter runs (think using more fuel). When this counter reaches it's value, or the DPF reaches a soot load of XX grams, the ECM will try to activate the regeneration process. This is the active part of the regeneration process. I haven't looked through the software enough to view the counter but it appears 50 hours is the magic number that the ECM will not exceed.

The two processes that are involved in a regeneration event are, De‐soot and De‐SOx.

The oxidation of diesel particulate matter (soot) begins at 1025 degrees Fahrenheit, oxides of sulfur (SOx) oxidation begins at 1185 degrees Fahrenheit. Since a lot of tractors never get worked hard enough to raise the exhaust temperature high enough to reach the threshold, a passive regeneration will never be achieved. These tractors will have to depend on the active regeneration process.* The active regeneration process on the LS XR/MT tractors runs at about 1200+ degrees Fahrenheit there by burning both soot and sulfur.