I picked up a M-Tuned fuel rail with K-Tuned AFPR off Facebook a few months back and after doing some research I was wondering if you guys could help me figure this one out.

When I got the stuff in the mail the AFPR had fittings on both sides with hoses attached to them and a fitting on the bottom with a hose. It also came with this T fitting.






After some research it seems the way to install the AFPR would be to run one return line from the rail to the AFPR and then plumb it into the stock return line next to intake manifold.

So HOW did this guy have this thing set up?! Any ideas how this would have been plumbed?

 

Most likely, he was using the T to make it a dual feed rail.

 

Unless I’m wrong, if this rail was dual feed then there wouldn’t be a place for the return line, unless that plugged hole on top is where the return line would have been. I’m thinking it was turned into dual return lines into the AFPR, and then a single line going to the factory line. But that doesn’t really make any sense to do it that way. I’m mostly trying to figure out how they were able to use both inlet ports on the AFPR, because every setup I’ve seen on miata only uses one inlet and plugs the other.

 

One side is feed to the fpr, the lower port is return to the tank, the other side is feed to the T, which T’s to both sides of the rail.

 

This fuel rail looks like it doesn’t have a lower port. You’re talking about on the underside of the rail, there’s like a flange machined into it with 2 bolt holes and a bigger hole in the center of those 2 but the hole leads to nowhere. It looks like it does nothing

 

C’mon Curly, draw a picture.

 

 

Red, you’re killin me. See pic below:

 

Okay, my understanding is that you were supposed to interrupt the supply line with the AFPR, that the supply line ran straight to the rail and then the return line tan through the AFPR.

 

I’m making no recommendations. I’m only showing what I understand Curly is trying to convey to you. That answers your question as to what the Tee was for; and why there were 3 hoses connected to the AFPR.

It it is up to you to decide why you bought this and how you wish to use it. I presume it was to be able to run higher fuel pressures.

See this Here it is recommend to use a damper by drilling out that middle boss and mounting it there, if 99 or up. Possibly for all that are dual fed? IDK. Maybe best to get a recommendation from the company.

DNM

 

DNM thanks for your input. Initially I only bought this setup for the injectors which I have since sold in favor of some brand new DW 700cc injectors. I will not need this AFPR unless I one day decide to upgrade my entire drivetrain in search of 400+whp on E85. For now the rail and the injectors should get me where I want to be for some time.

Right around the time when you posted this I saw somewhere else a diagram of someone running the AFPR this way. That doesn’t really make sense to me to put the AFPR in the feed line, but it is apparently one way to set it up. Weird.

One more question. I am running a standalone ECU and considering upgrading my fuel pump to Walbro 255 I’ve read reports of this pump overloading the stock FPR causing a rich condition at idle. Is this a condition that is consistent and therefore would be easily managed with a standalone, or is this something that is sporadic and unpredictable in which case I would remove the stock FPR and install this one

 

If you think about it, this is how the factory does it.

The FRP is mounted to the fuel rail, which is a metal extension of the feed line. It holds until the set 43.5psi, dumping excess in the return line. This setup simply moves the aftermarket FPR off the rail with a rubber hose.

I've tuned cars with the 255 for a decent idle without issue, but I don't like it. An AFPR adds a lot of hoses and complication in the engine bay, so if it isn't absolutely necessary, I wouldn't use it. The best thing the AFPR can do is give you the ability to go from 3 bar to 4 bar, increasing headroom if your injectors are slightly undersized.