940 fuel problem

my 940 gl sometimes stops running with about 1/4 tank of fuel.sometimes the emission light will come on with the code fuel 1-2-1(maf signal absent or faulty) and ignition code 1-4-4(load signal from fuel injection system absent).i was told on a previous post that the bellows on the intank pump could be split.i have just got the pump out of the tank and it is a sealed unit.i have just read about the fuel pump relay and about the main fuel pump.can i check these with the other pump out of the tank?and if so how.and any other ideas would be welcome.