The ECM/PCM depends on the data coming from this dual sensor (AKA MAP Sensor but refered to as Boost Pressure Sensor in FSM) - both intake air temperature and air pressure are measured with this sensor. The ECM/PCM in turn uses this information to calculate how much fuel to inject into the cylinders - so this sensor has a direct relationship to the power, efficiency, fuel economy and soot output of the engine. The egr design is going to be an ongoing maintenance issue with this and any other egr equipped diesel. This soot will cause degraded sensor performance problems due to carbon buildup in the intake system and anything in its path negatively affected by soot and carbon buildup. It will also affect ring wear and engine longevity. I use chlorine free disk brake cleaner from the auto parts store to clean the sensor. That said I not sure if any cleaner we could buy at the parts store would harm the sensor seeing how "tuff" this thing has to be to work where it is located.
Ranger1's thinking is (I agree) with all that soot buildup, the ECM was using stored values, as temperature and boost couldn't possibly be measured correctly with that clogging. I'm deducing that on the temperature, the soot acted as an insulator, keeping the cold readings for too long on warmup, causing overfueling, and kept heat on the sensor once the engine was up to temperature, causing underfueling on longer trips.
This looks to be a 5000 mile/7500 kilometers cleaning job to have a proper running engine with current fuel. We can only hope ULSD may drastically change this for us.
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1. This is the sensor after removal, it requires a 4 mm allen wrench and I left the wiring attached in case I dropped the thing while removing. There is a tension washer under the screw and will require a magnet most likely to remove it from the manifold. Just lift the tab and pull the sensor off the warring harness. I didn't disconnect the battery before doing the cleaning, but I had no problem. However it might be wise to disconnect the cables to prevent any problems. One thing I did was remove the three holding nuts for the wiring harness to ease removal, but it is probably not necessary for most people.
2. This is where it pluggs into on the manifold.
3. This is a members sensor and it is solid crud.
4. This is the sensor from my CRD at 21,700 miles, and it was packed solid.
5. This is mine after cleaning.
Maybe it's time for a Provent.
