???? Is the MAP sensor the same as the boost pressure sensor?
The process of making the diesel engine run isn't complicated. The induction stroke pulls in a gut full of air and then at the ignition stroke fuel is injected into this air at very high pressure.
On older diesels the turbo effectively increased the displacement of the cylinders by introducing more air into the system at higher than atmospheric pressure. Add more fuel to this extra air and you've got a bigger bang, so more power.
In modern diesels the turbos role has changed. The green lobby don't like over fueling as this leads to nasties in the exhaust so the turbos role is to always ensure there is more than enough air for the fuel load that is injected to burn completely.
So in the TD4 design the turbo actively adapts to prove useful boost from idle speed upwards. This means plenty of capture of these exhaust gases to keep the turbine speed high enough to have an effect. However, when the revs are up and the power is really on then this arrangement will cause an overboost. Therefore an actuator operates vanes which steer the exhaust gases off the turbine blades to reduce the turbine speed and limit the boost pressure level. The turbos job is to make the engibne burn clean rather than for outright performance.
This change in design is clearly seen by the fact that the boost pressure is so low. Where the TD4 operates at 1 bar, the L series operates at 1.7 bar. Howver, without the turbo the L series will still run at low power levels. I had to limp home with a blown induction hose fitting. There was no boost at all and the engine was running effectively naturally asperated. It ran but I could do little more than about 40 MPH.
The Manifold absolute pressure sensor relays the air pressure that is entering the cylinders back to the ECU. This information will be used to determine 'Green' fueling levels. The Turbo boost sensor will monitor the pressure at the turbo discharge port and is more likely to control the boost limiting vane position. Between these two is the intercooler which will effect a pressure difference between the two sensors. Again the L series only has the boost sensor so to be able to determine the additional fueling demand as the turbo spools up.
If you are experiencing misfire then the fuel system is the only place to be. Either the ECU is miscalculating injection timing because of duff asperation data, which seems unlikely after all this work, or the injector are opening but there is too low a fuel pressure behind them to cause a good enough spray pattern or deliver enough fuel.
By all means elliminate the MAF sensor, my money is still on the fuel pumps myself.
Good luck.
