Fuel pressure, how much is too much

[tomtietjen]

I put a pressure gage on the feed line to the pressure regulator today and it's reading about 55 psi. Bike is a 2004 r1150GS.
I see in the shop manual that it should be 43.5 psi. but I'm wondering that if there are no fuel line leaks would the extra pressure really hurt anything?
The bike runs fine and gets the same fuel mileage it allways has. There is no restriction in the return line and the pressure is the same if the line is connected to the tank or free flowing into an gas can. I hate to lift the frame again ( just did last winter to grease splines ) but I would like to relocate the regulator so its exposed somewhere.

 

[AntonLargiader]

Do you trust that pressure gauge? The regulators are pretty accurate.

 

[tomtietjen]

Good point, maybe before I tear into it I'll try another gage.

 

[scott.lambert]

I put a pressure gage on the feed line to the pressure regulator today and it's reading about 55 psi. Bike is a 2004 r1150GS.
I see in the shop manual that it should be 43.5 psi. but I'm wondering that if there are no fuel line leaks would the extra pressure really hurt anything?
The bike runs fine and gets the same fuel mileage it allways has. There is no restriction in the return line and the pressure is the same if the line is connected to the tank or free flowing into an gas can. I hate to lift the frame again ( just did last winter to grease splines ) but I would like to relocate the regulator so its exposed somewhere.

Sorry if this is a dumb question. You say you are measuring on the feed line "to the regulator" ?
Shouldn't you be measuring on the output side of the regulator?
I would expect the input side to fluctuate a bit.

 

[roger 04 rt]

Do you trust that pressure gauge? The regulators are pretty accurate.

Anton's right about that. It's a spring and diaphram. Not much to go wrong.

If the pressure were 55 psi your injectors would deliver about 12% more fuel than the Motroniic expects. After time though, the Motronic would adapt to it.

There is a 3.5 bar regulator from the K1200RS that fits the R1150. If someone installed it the approximate pressure would be 51 psi.

If you had that regulator and added a BMW-AF-XIED set to AFR 13.8:1 you'd have a pretty sweet running bike.

 

[JamesInCA]

Is there a problem you're trying to fix?

"If it ain't broke...."

 

[JamesInCA]

Sorry if this is a dumb question. You say you are measuring on the feed line "to the regulator" ?
Shouldn't you be measuring on the output side of the regulator?
I would expect the input side to fluctuate a bit.

You measure fuel pressure on the supply line (from the fuel tank/pump output to the FPR & injectors).

The FPR sits after the injectors in the fuel plumbing. As Roger notes, it consists of a spring pressing a diaphragm against the return line to the tank, closing off the return line and preventing fuel from exiting to the tank. The fuel pump pumps fuel into the system. When the pressure of the pumped fuel exceeds the force of the spring, the diaphragm opens and fuel passes through into the return line. The pressure at the supply line and the fuel injectors will be the same, as they're all effectively a single tube.

You also wouldn't expect to see a difference in pressure (on the supply line) with the return line free vs. connected to the tank -- unless there were some sort of obstruction in the tank return plumbing, in which case the pressure would be higher everywhere in the system.

 

[scott.lambert]

You measure fuel pressure on the supply line (from the fuel tank/pump output to the FPR & injectors).

The FPR sits after the injectors in the fuel plumbing. As Roger notes, it consists of a spring pressing a diaphragm against the return line to the tank, closing off the return line and preventing fuel from exiting to the tank. The fuel pump pumps fuel into the system. When the pressure of the pumped fuel exceeds the force of the spring, the diaphragm opens and fuel passes through into the return line. The pressure at the supply line and the fuel injectors will be the same, as they're all effectively a single tube.

You also wouldn't expect to see a difference in pressure (on the supply line) with the return line free vs. connected to the tank -- unless there were some sort of obstruction in the tank return plumbing, in which case the pressure would be higher everywhere in the system.

Thank you. I was imagining a setup more like my gas grill. I'm going to try to acquire some metal QDs in preparation for the next time I have to take the plastic off.

 

[R100RTurbo]

As to the effects of higher pressure, at a certain point high Z injectors will not want to open due to the fuel pressure being too high. I ran a set of Delphi 45lbers (Bosch EV1 style) at 100psi inadvertently and they were still operational.