Aftermarket Fuel Pressure Regulator?

[james12lucy]

Hey all.

So, as you may know, I’m upgrading one of my B7s. As part of the upgrade path, I’ve been reconstructing the fuel system to do away with the OEM tank and LPFP setup.

To this point, I’ve put together a trunk mounted, 17 gallon fuel cell, twin Walbro 485 pumps, AEM 7 micron fuel filter, and Torqbyte CM5-LT and PM3 to control it. It’ll retain OEM control over both pumps, and will prime when the door opens, etc.

The issue I’m struggling with, is if I’ll really need an inline fuel pressure regulator? I know the OEM filter has an inbuilt 6BAR regulator, but I’ve done away with the OEM filter. Since the HPFP has a fuel pressure regulator to sort out anything over 165BAR, the injectors will never see pulses associated with port injectors. My question is this; will possible low pressure pulses adversely effect my HPFP? I know it’ll sort out the fuel and return it, but I’m worried about the fuel between the LPFP and HPFP.

Please feel free to chime in. Thanks AZ.




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[aluthman]

The stock lpfp is controlled via PWM to regulate pressure. The regulator in the fuel filter is more of a backup overpressure relief. You should be fine if your walbros retain PWM control, but if you wanted to put in a FPR inline, it wouldn't hurt anything.

[StatusQuo]

In my opinion I don't think we even need a fuel pressure regulator on the low side. As you said, the HPFP system regulates it itself and the low side will never get above 50bar anyways. I think it's more of a safety thing by the factory. As above said, if you got PWM, you should be fine.

*Ninja edit* I wouldn't tune to 10bar. Might throw codes

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[aluthman]

I gather from your OP that you're adding port injection? If so, the low side for the port injection and hpfp should be maintained separate. The large pressure changes in the low side will make it a nightmare to try to tune the port injectors. You just need to run one pump for each half.

[james12lucy]

I gather from your OP that you're adding port injection? If so, the low side for the port injection and hpfp should be maintained separate. The large pressure changes in the low side will make it a nightmare to try to tune the port injectors. You just need to run one pump for each half.

Thanks for the heads up, fellas. I will be retaining PWM control with the PM3, so I’ll pass on the fuel pressure regulator.

Adam, not going port injection this year, but didn’t want to rule it out. I’m running both pumps to ensure there is zero starvation issues. Both of those fuel baskets have ball valves and will be connected via a -8 line to share fuel when pulling G’s. It was a cheaper and simpler solution to adding a secondary or cell mounted surge tank. Also, it keeps the pumps submerged, which will keep them running more efficiently.

If I decide to add port, I’ll add a fuel pressure regulator, but I doubt that’ll be this year. I’ve already sourced a 034 Motorsports EFI controller, but am not sure if I should pull the trigger. Ultimately, I think dual fueling is a great idea, but the car is an endurance car, so efficiency is also a premium. Also, building the head makes more sense before I add a third fuel source (I’ll be spraying meth).

Thanks again, fellas.


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[aluthman]

In that case, run it without an FPR unless it starts to give you issues.My only question I guess is why so much low pressure fueling when you are severely limited by output of S3 injectors?

[james12lucy]

In that case, run it without an FPR unless it starts to give you issues.My only question I guess is why so much low pressure fueling when you are severely limited by output of S3 injectors?

That’s a solid question. Redundancy. I’m okay with Over fueling and not starving for fuel in a high G corners. And I’m totally OK if I drop one pump well racing.


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[aluthman]

Fair enough.

[derrek]

You’re going to throw codes for the low pressure side exceeding the pressure range it’s setup for. You can change the range with winols, not sure if maestro gives you that option though.


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[james12lucy]

You’re going to throw codes for the low pressure side exceeding the pressure range it’s setup for. You can change the range with winols, not sure if maestro gives you that option though.


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Thanks, I hadn’t actually thought about that. I will look into changing it. But if it was a cold and doesn’t go into limp mode, I really don’t care. It’s not like the car is without 1 million codes anyways, I have eradicated it most of the CANBUS system.


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[derrek]

Thanks, I hadn’t actually thought about that. I will look into changing it. But if it was a cold and doesn’t go into limp mode, I really don’t care. It’s not like the car is without 1 million codes anyways, I have eradicated it most of the CANBUS system.


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It messes something up, don’t remember right now as I haven’t done very much b7 stuff this year. It was a problem though.


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[aluthman]

You’re going to throw codes for the low pressure side exceeding the pressure range it’s setup for. You can change the range with winols, not sure if maestro gives you that option though.


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IIRC, you can change that in maestro.

[james12lucy]

IIRC, you can change that in maestro.

Awesome. So what do I do? Just log at WOT and set min/max?


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[Joshlc1988]

I don't think your going to get by without a regulator. I would think you would have to modify every map that sees a pwm change.correct me if I'm wrong but my understanding is the pwm signal grounds the pump, in turn giving it 100% power for that pulse. Those walbros have around a 120 psi max each. So their gonna try to push over 8 bar every time the signal is sent.
Example: say 30% duty is 30 pulses every 60 seconds. So the pumps are gonna go wide open 30 times every 60 seconds. That's over 8 bar pulsing up to the hpfp. I would think that it would be hard to tune for that.


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