Where should a fuel pressure gauge and regulator be placed?

[4gfun]

I'd like to add a fuel pressure gauge and a fuel pressure regulator. It is a Galant VR4, so where would the best place to put these items be on a 1g?

Thanks

 

[4gfun]

Thanks...that is where most of my gauges started off but moved them up above the radio (GVR4 style).

I think it is back to the glove box for me honestly.

Glowshift makes pretty decent gauges. I've used their mechanical boost gauge before but I can't really vouch for the quality of the electronic gauges/senders. Prosport is another brand you may want to look into that doesn't cost an arm and a leg. I will be changing my fuel setup soon and will be mounting my fuel pressure gauge inside. Have a glovebox setup I'll be trying to whip up for secondary gauges that I won't need to keep an eye on consistently but will be good to have

 

[project98dsm]

I may be wrong but I'm pretty sure the fuel pressure doesn't necessarily drop after the injectors. Think of fluid dynamics. Regardless of where your regulator is mounted...it will control the fuel pressure of what is BEFORE the regulator. If mounted at the end of the rail, the injectors are feeding off of 43psi (for example) of fuel pressure. If mounted on the firewall after the rail, the injectors are still feeding off 43psi of fuel pressure. If you mount the regulator before the injectors, the fuel pressure before the regulator will be at 43psi and the fuel pressure AFTER the regulator will be (y)psi, which will basically be what's bypassing the regulator's mechanism to maintain constant pressure and will not be supplying the injectors with the required fuel pressure to feed from.

 

[4gfun]

Thanks for taking the time to explain this. I can't see any reason why you would not be correct

If someone wants to come in and advise why that is incorrect then I guess we can take a listen....but if no one else cares to rebut then I'll just put the gauge back there!

I may be wrong but I'm pretty sure the fuel pressure doesn't necessarily drop after the injectors. Think of fluid dynamics. Regardless of where your regulator is mounted...it will control the fuel pressure of what is BEFORE the regulator. If mounted at the end of the rail, the injectors are feeding off of 43psi (for example) of fuel pressure. If mounted on the firewall after the rail, the injectors are still feeding off 43psi of fuel pressure. If you mount the regulator before the injectors, the fuel pressure before the regulator will be at 43psi and the fuel pressure AFTER the regulator will be (y)psi, which will basically be what's bypassing the regulator's mechanism to maintain constant pressure and will not be supplying the injectors with the required fuel pressure to feed from.

 

[Afizzle]

proper way imo is to remove emissions and mount the fpr in an attractive spot anywhere on your now cleaned up firewall

 

[WES_393]

If you mount the regulator before the injectors, the fuel pressure before the regulator will be at 43psi and the fuel pressure AFTER the regulator will be (y)psi, which will basically be what's bypassing the regulator's mechanism to maintain constant pressure and will not be supplying the injectors with the required fuel pressure to feed from.

Yes, you are correct. The FPR regulates pressure within the fuel rail by bleeding off excess fuel, which then runs back to the fuel tank through the return line. If the FPR was regulating pressure before the fuel rail, then the injectors would only receive the excess fuel shed by the FPR.

If that is the case, and I go with this setup, could I run some fuel line temporarily and extend the gauge to my windshield via duct tape just to see what the fuel pressure is at WOT?

I think that this is overkill if I am trying to rule out fuel issues but not sure.

A pressure gauge or sending unit tapped into the fuel system would work. It's easiest to adapt the gauge/sender right at the filter like Project98 mentioned. I'd highly suggest using an electronic gauge instead of extending a mechanical one. If you must, be sure to use fuel injection safe hose, bard fittings, and clamps.

However, a high quality (Aeromotive, Fuelab, etc) Adjustable FPR is never wasted money. They can be found new with install kit for a little over $200, but usually go for around $100 used.

 

[NHerron]

The common FPR that us DSM people have is either the Aeromotive 13101 or 13109. It is a bypass regulator designed for electronic fuel injection with fuel return.

Fluid pressure is equal in all directions between it's flow origin and it's flow restriction. In our case the only restriction would be as designed, the fuel regulator. Things like line ID size, bends and kinks don't cause a restriction until you're flowing a ton of fluid (bigger injectors @ high injector duty cycles [IDC]) so don't worry about that stuff.

In all technicality, you can place these Aeromotive FPR's anywhere you want. After the rail, before the rail, after the pump, right before the tank etc. As long as it bypasses enough fuel to only let the injectors see 43psi base pressure, it's all good.

I think the most confusing part is understanding how the bypass regulator actually works. Regulator is just a general term, it does not specify the way one actually regulates. Now think about the word BYPASS. That is the key, the subcategory of regulators. When people think of restrict they think of a bottleneck between two points. That's not how this works. In fact it doesn't directly restrict flow to the injectors at all. Imagine taking a pump and capping the oulet off. Plug it in and see what happens first. Either the pump goes up in smoke (if it's unfused) or the cap flys off. The cap restricts the flow from the pump so positive pressure builds rapidly at the outlet until something gives.
Now this time before the pump burns up drill a small hole in the cap and pressure will be relieved but there's still alot there. The pump is trying to move a certain volume but can't -the hole isn't big enough so the pressure only declines slightly. But keep drilling until you see 43psi at the cap. It is now bypassing enough fluid for the cap to see 43psi. Vice versa, plug the pump in with no cap, no restriction. There is no pressure there because it's flow is not restricted.

Imagine the cap as an injector in the same scenarios above. Would it matter where this relief hole is drilled? As long as it's keeping the 43psi maintained it doesn't right? Now imagine a small pipe and enough room to hold 4 injectors at the end of the pump. Still no difference. If there was no relief hole, the pump would burn up or something else would give. Too big a hole and all fuel bypasses injectors AKA no pressure seen by injectors.

Most companies will recommend after the rail. But that is for reasons unrelated to the above and how they work foundationally. If the FPR was before the rail, the rail would need be plugged so the only way out is the FPR discharge port.

 

[4gfun]

Thanks for all of the help!

 

[NHerron]

No problem pimpin

 

[project98dsm]

I have never seen a return setup with a regulator before the injectors. Sounds like a lot of unnecessary work to get the desired fuel pressure "post regulator/pre injectors". Our cars came from the factory with the regulator after the rail, so why go through all of the trouble to change it? I'm not saying it won't work. I'm saying I've never seen the setup nor heard of it.

 

[NHerron]

I agree, just run it after the rail it's easier. 90% people here run after the rail for that reason. But the OP seemed curious so I do what I can to explain in a way that makes sense.

Alot of late model cars use a bypass regulator right after the pump, that way it's simply all in the tank.
Some aeromotive info:
Aeromotive |  FAQ – EFI Regulators

 

[Rsawd95dsm]

So after the fuel enters the fuel rail where does it go? The fuel rail is the last place fuel goes before it hit's the injectors and enters the combustion chamber. So the AFPR has to be installed before the fuel rail not after.

WES put up a picture right before you posted. You coulda looked at that pic and took advise from a well experience guy and seen his is run the correct way.

 

[NHerron]

I might be reading this thread wrong lately but...
Don't get all excited and think I'm arguing about where to put the regulator. Just giving the OP a good explanation on regulators. Simple enough I thought, didn't think it would cause grief.

I run it after the rail BTW.

Good luck in that box.