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I can help you out.
However, let me ask you the vehicle's symptoms.
Obviously it cranks but it won't start.
Do you have spark?
Do you have fuel pressure?
Do you have injector pulse?
The fuel regulator works off engine vacuum. The less vacuum, the regulator closes(wide open throttle and starting conditions). When there is engine vacuum, the regulator opens (idle and stable driving). So, if it is stuck open... remove the return line and see if fuel comes out of the regulator. There should be none when the engine is not producing vacuum.
Yes if you have no fuel pressure, you must verify power at the pump. Then check for any line restrictions such as a plugged filter and kinked lines. If that is ok, look for a stuck open regulator. However, you must check fuel pressure with a gage for most accurate readings.
Checking for spark will also let you know if that is actually the problem. So, start there.
If you have good spark, good fuel pump power, no line restrictions, the regulator would be the next thing to investigate.
The MAF sensor only tells the computer how long the injectors must stay open in millisecond time. (injector pulse width)
Fuel tank pressure sensor is used for Evaporative Emissions and is not used for drivability purposes.
The Intake sensor is used in combination with the MAF to determine injector pulse width.
The chassis acceleration sensor is used for injector pulse width.
Engine coolant temperature sensor is used for injector pulse width.
The throttle position sensor is used for injector pulse width.
The knock sensor is used to detect detonation.
These are all computer inputs and fine tune the engine management system. They work in no particular order. The computer is what turns on the fuel pump using the main relay and the fuel pump relay. The fuel pump turns on for about one second when the ignition switch is turned to the on position. The fuel pump also turns on when the ignition switch is turned to the crank position. Once computer notices the vehicle is running through the crank sensor, the fuel pump does not shut off until one second after the engine is stopped.
Plese let me know if any part of your question went unanswered.
2003 Jetta left rear window blue plastic part of the