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  #11  
Old 03-26-2020, 04:49 PM
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Wow that’s just “crazy talk” I’ve only seen it sold in conjunction with the filter. Since the filter really is literally a “million mile” filter being on the order of 200-400x the size of inline filters I’ve changed in my life, it is promising that it could be possible to just change the regulator.

I have to squash a bug on wife’s car that acted like fuel pump failure but the pump was still running. could be the fpr.
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  #12  
Old 03-26-2020, 06:37 PM
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Petrol models don't have sensor for fuel pressure. Fuel pressure is regulated with intake manifold vacuum connected to regulator.

Older M57 diesels have supply pressure sensor on top of fuel filter in engine bay. Newer facelift M57N engines have fuel filter under car and no sensor for supply pressure.
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  #13  
Old 03-26-2020, 07:39 PM
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Quote:
Originally Posted by Clavurion View Post
Petrol models don't have sensor for fuel pressure. Fuel pressure is regulated with intake manifold vacuum connected to regulator.
...
But, for example on my 2001 3.0i's M54B30 gasoline engine, that vacuum hose from the fuel pressure regulator that is built into the fuel filter connects to the intake boot, which is upstream of the throttle plate, so it is not at manifold pressure. It's pretty much atmospheric pressure there, varying hardly at all with velocity or ambient atmospheric pressure.

My understanding, from reading stuff and thinking about what makes sense (i.e., I don't definitively know this) is that it is for venting a tiny amount of gasoline vapor into the intake rather than to the atmosphere, for emissions reasons.

I've also seen it said that it is in case there is a failure at the regulator that causes gasoline to leak it goes into the intake. That to me sounds like the opposite of what you'd want.

Have also seen it said that it provides an atmospheric pressure reference for the spring regulator, and taking it from the intake boot means it is filtered. Seems like a lot of work to me to get clean air back there.
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Old 03-26-2020, 08:50 PM
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@clavurion: the vacuum tube to the fpr is not for regulation. I think it’s to suck in the 6 molecules per year of gas that somehow eek out of the fpr and make sure they don’t kill the whole world.

Oldskewl is correct the fpr is a mechanical FPR.
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  #15  
Old 03-26-2020, 09:10 PM
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Now that you say it there's not much that vacuum line could do on M54 when it's connected before throttle valve.
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Old 03-26-2020, 09:15 PM
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Yes, the fuel pressure regulator is just vented to the intake boot because the line was already there and blocking it isn't an option. The actual engine running rail pressure is determined by the relief valve on the end of the siphon-jet assembly in the tank.
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