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It is internal under the upper intake manifold.
Here's what it looks like after the upper intake is removed.
No, that doesn't sound like a regulator problem but it is possible. You will need to run some tests to determine what the problem is.
The first thing yoiu need to do is use a fuel pressure gage to determine the exact fuel pressure. This is a high pressure system and a loss of merely a couple pounds and it won't start.
You need a minimum of 55 PSI to run. If you don't have that, then try pinching off the return line and see if that makes the pressure spike. If it does, then you could start to blame the regulator. If not, it's likely the pump.
2003 Jetta left rear window blue plastic part of the