B_Swapped93

I've got 2 -8AN feed/return lines sitting on my bay ready to be fitted/connected to the FPR/rail. Before I put the fittings on, i'd like to check this routing is correct. I've included a picture of someone else's set up, this is how I plan to rout me. My only question is I see ppl run 3 lines off the FPR, but i'm assuming they're running the stock hardline or a show car with a returnless set. My plan is, inline filter than feed directly into the rail w/ U-joint, then return directly into the FPR then going back to the tank.

My set up is
ID2000s
walbro 450lph

JRCivic1

For a return style fuel system, what you have described (and pictured) is absolutely correct. Routing can be accomplished many different ways, however, the general order must be followed: Fuel pump -> Fuel filter -> Fuel rail -> Fuel Pressure Regulator -> Fuel return to tank. In the photo that you posted, the unused horizontal fitting with the sealing cap installed would normally be used with a second fuel rail... either in a V6 or V8 application OR a twin fuel railed 8 injector 4-cylinder application, in which case, you would "Y" or split the feed line between the fuel filter and both fuel rails and then the pair of lines exiting each of the two fuel rails would go to both horizontal fittings on the fuel pressure regulator. The bottom fitting on the FPR is the return to the tank.

B_Swapped93

Thanks for clearing that up, confirming.

B_Swapped93

So, instead of making a new thread. I've got 2 questions. 1: is there any harm in having the FPR mounted right after(on) the rail, as in attached to the rail it's self via the correct fitting. Next, this little vac port-nipple, I don't see anyone using it really, can I just cap it off? I'm running the ktuned intake manifold and my 3 ports are spoken for with the my brake booster, waste-gate and BOV.

B_Swapped93

BUMP, fuel set up coming Friday, need to know these questions.

mk378

I'd be concerned about vibration breaking the fitting with a direct mount on the end of the fuel rail like that. For sure, don't use a brass nipple.

The vacuum compensator is used to make the fuel pressure follow the manifold pressure so the drop across the injectors stays constant. The stock ECU software requires that. Many other systems do the compensation in software.

B_Swapped93

Should state the specs: All fittings are high quality K-tuned fittings I've seen lots of high hp cars run it on the rail, i'm curious if it would affect the reading being so close. ID 2000s and running K-pro v3. I don't see many(any) turbo K guys using that nipple, that's why I'm asking, hoping someone with a kswap will respond.


Remember, on the B/D/H engines the FPR HAS to sit on the rail, and that's with some tiny m8 bolts from the factory... i'm running -8 AN fittings/lines.

CX-Adam

TL:DR: This is a good question and it's making me wonder a few things, too. Based on my ramblings at the end of this post, you might want to consider installing a T in one of the lines you mentioned. Also, I know with my supercharger I'm supposed to have my FPR vacuum line attached to my manifold downstream of the blower. But, I'm running the stock FPR so that may be a factor.

Whether or not they're K-tuned parts or even if it's a K or B series shouldn't matter if we're talking general system functions.

Hopefully someone like JRCivic jumps in with some experience.

Everything that follows is me talking to myself trying to figure out how the fuel system works.
I don't completely understand how the FPR is supposed to operate when the engine is under load. In an NA car, there's still some vacuum in the manifold so the FPR might be open a little. There's obviously boost in a boosted car and, if the FPR is connected to the manifold, that'll definitely keep the FPR closed which might cause some fuel pressure spikes and may affect injector operation. (key words: "might" and "may")

Our fuel rails have a low pass and high pass filter on them (signal noise filters). The high frequency spikes cause by a constant fuel pump pressure source but only periodic openings that aren't perfect square waves by the injectors are filtered by the damper on one end of the rail. The low frequency (slower moving) pulses are filtered by the FPR. My understanding is that the FPR keeps the fuel pressure in the rail below the set points of the injectors. It opens when the dP across the internal diaphragm exceeds the spring pressure keeping it closed. On one side of the diaphragm you have the fuel pressure trying to open the valve. On the other side of the diaphragm, you've manifold vacuum (on an NA car) ALSO trying to open the valve.

When going from WOT to idle the FPR keeps the pressure in the rail below the maximum pressure that the injectors can open against with some margin. This is where setting your injector dead times in the tune comes into play because they're fuel pressure dependent. At idle, the intake manifold is in vacuum in both boosted and NA setups. However, I don't know if the increased closing pressure on the FPR is a bad thing once the engine is loaded. Basically, I don't know if it should be slightly open at low loads.

mk378

The fuel pump pumps faster than engine will ever use it. The fuel pressure regulator is always partway open and letting the excess fuel return to the tank.

The pressure at which the regulator runs open is determined by a spring and the manifold vacuum. With the vacuum port left open, only the spring is at work and it sets the pressure to about 40 psi on a stock regulator. The vacuum pulls against the spring on the non-fuel side of the diaphraghm and causes the valve to open at a lower pressure with more vacuum applied. Thus more manifold vacuum - lower fuel rail pressure. Boost pressure does the opposite. Boost pressure in the manifold - higher fuel rail pressure.

CX-Adam

Thanks. That clarifies a few things for me and reinforces the remainder of what I said. I haven't had much chance to drive my car so I haven't been able to watch my fuel pressure under load.

So, he should set his injector dead times based his fuel pump rating and not run a vacuum line?

B_Swapped93

So a VAC line is a must pretty well? if need be I can T the WG or BOV but I only have 2 ports left that's why i'm worried. So, we all agree it's ok for me to have it on the end of the rail? I don't think it'll break a -8an fitting. Thanks for the responses, maybe it's a show car thing. The posts I am referring to are the guys with huge followings on IG.

CX-Adam

If you're concerned about vibrations causing a failure, don't be.