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Q: why can't the MPS be repaired? Can it be re-engineered?

The D-Jet MPS is, at this age, now prone to failure. The usual failure is the diaphram breaks, and the device no longer senses pressure changes. This would be no problem, if there were a source of replacement diaphrams. However, the original units were made of some exotic material like beryllium-copper alloy, which is not readily available to produce replacements. Attempts to duplicate the part in other materials have met with generally negative results. The only reliable source for the parts are other used MPSes. The MPSes are not all the same, but the diaphrams are, and interchange.

There are modern pressure sensors available that are solid-state, very reliable, readily available, and not expensive ($20-50). However, these generate a variable resistance based on absolute pressure. The D-Jet MPS does NOT use variable resistance, but instead uses the variable inductance of a coil with a movable armature to phase shift a square wave generated by the trigger points. The MPS used with the Type IV has TWO coils, and feeds back the output of the first coil into the second along with a voltage provided by the air temp sensor. This makes the MPS a genuine air-density sensor (pressure and temp determine density), not just a pressure sensor.

Duplicating the effect of the MPS using a MAP sensor, a temp sensor, and some electronics would be possible. However, the complexity of these electronics would approach that of a full fuel-only ECU. You'd need some way of reading the variable resistance MAP and air temp sensors and the trigger point's square wave, and output a square wave calculated from the sum of these inputs. This would really require a microcontroller (I'm sure it could be done using all analog parts, but probably only with a large parts count), which would have, using the simplest approach, a 3D map of rpm (read from the square wave in) and air pressure, with a 2D correction map for air temp. This is, essentially, all most fuel-only ECUs do. No cold-start or warm-up enrichment system would be required (provided separately on D-Jet), nor would you need the injector driver circuitry. Still, the jump from this to a full replacement ECU that uses a normal tach input (no trigger points, so any distributor could be used) and an off-the-shelf MAP sensor is fairly small, and you could also remove the aging (and sometimes troublesome) cold start system from the D-Jet as well as the MPS with a full replacement ECU.