After months of flip-flopping on the idea of going "return" on my 99, I have decided not only to attempt the conversion, but do a step by step how to of my failures along the way.

Anyway, I have a build thread in 'media' but basically I have a '99 with a built engine with most of the supporting mods and an EMB controlling yellow rx8 injectors, pushing stock NB fuel pressures with a walbro 190hp in the tank and a stock nb rail. I've been running 14-15psi for the last year or so and I've basically been maxing out the DC of the injectors and still running kinda lean at that psi.

I went out to the dragway a few weeks ago and ran IMO, shitty times for what I have into the car. Not to mention my clutch slipping pretty badly. So, like most trips out to the dragway or the dyno, I felt the need to spend a bunch of money to make the car even faster.

I know, I know, why don't I just buy some 1000cc injectors and a standalone and be done with it? Because **** it, that's why!

And now without further ado...
This is the stock location of the fuel filter, pressure/return lines, and evap return line. I previously removed the charcoal canister and protective cover
I did most of this work last night in my garage after numerous bud lights, so unfortunately I forgot to take pics of certain things(like pulling the sending unit and removing the in tank FPR.) but that is pretty self-explanatory and if you can't handle doing that, you probably shouldn't attempt this DIY.

Next step is to remove the stock pressure/return line from after the filter. You want to disconnect the exit side of the fuel filter and the part that connects to the 5/16in pressure line that goes up to the fuel rail. After you do that, go back up top to the sending unit and disconnect the return side. This hard plastic line is all one piece and has 3-4 brackets holding it in place between the front of the fuel tank and the body. You need to pop the line from the brackets on the top side and the bottom side, then carefully pull it free of the car from the bottom. It looks like this once it's removed.



Next, I used some 5/16 hi-pressure fuel hose and a 90 degree quick disconnect to attach to the return side of the sending unit and ran the hose along the same path as the hard line I just removed.

You can kinda see the hose running across and down the tank in this pic


Now back under the car, you can see I attached the other end of the 5/16 hose to an aluminum 5/16in to 1/4in adapter and then used an additional couple inches of hose to attach that to the stock 1/4in evap line that runs up to the engine compartment next to the 1st pulsation dampener. If you notice from the before/after, I had to carefully twist the evap line upward.
You'll also notice I created another line between the filter outlet and the pressure feed hardline that leads up to the rail. Once it looks like this, you can move on to the engine compartment.



More to come...

 

Here are the regulators. left NB, right NA.


Above the BOV you'll notice a 1/4in evap line pointing straight up. That's the new return line.

Now pull the upper manifold to gain access to the fuel rail and pulsation dampener. You'll need to pull the rail away from the head a bit to access the dampener bolt on the vc side.


Pulse dampener

 

While you have all this opened up you should consider a separate relay off the battery to power the fuel pump.

 

This is on my to do list..... subbed.

 

Mount the NA fpr upside down and reattach the fuel rail being careful to properly seat the injectors.


The vacuum source I used was directly below the fpr, it's shared with the vics vacuum source. Just remove the vac cap and run about 3" of 1/4" vacuum hose to the fpr then re-install the upper plenum.



Once everything is back together run a 5/16" fuel hose off the top of it and toward your afpr.


I'm still waiting for my afpr to come in the mail. It was supposed to be here Saturday, so I'm hoping it''ll show up tomorrow. Until then, I decided to temporally use another 5/16" to 1/4" adapter and tap directly into the return line so I can at least fire it up and do some pressure testing.



It fired right up and surprisingly, once warm, it held pretty much the same afr's as before on 60psi on fuel pressure. You can definitely hear the fuel rushing through the hoses, it sounds badass. I'll probably have some pics up late tomorrow night if the part arrives.

 

Subbed.....doing this this week I believe......Thanks for the pics!

 

Awesome, I'm glad someone is documenting this.

I'm on a bunch of painkillers at the moment... but does using the vapor tap on top of the tank for the return make a bunch of fuel splashing noise?

Edit: Wait, am I stupid? Is that round gold thing with the hose coming out of it the vapor tap? On my 2000 the fuel return after the in-tank regulator was inside the tank. I'm having a hard time figuring out what that second fitting is on top of the sending unit/pump mounting plate.

 

The NB actually does have a return line stock, and its already ran back into the sending unit and flows fuel through the in tank fpr. That's why the hard plastic line has three ends. Basically all your doing with this mod is creating a dedicated pressure line fom the filter exit to the hard feed line and using the existing evap line to create a dedicated return to the sending unit.

The only part of the new system that sees pressures higher than 10-15psi is the the 8in of hose between filter and the feed line. If I have any leakage issues once the afpr is installed and the pressures are higher, I'll probably custom bend some steel line to replace the hose.

I should also mention that I removed the convertible top years ago, so accessing the sending unit was painless. Your results may vary. I also removed the vapor filter that attaches to the evap hard line in the engine bay long ago. That must also be deleted to do this mod if you don't want to run an additional return line.

 

Ok, that makes more sense... I guess. Silly Mazda, now that I'm thinking about it, it seems like it would have been a lot easier to just put a legit return in the car

Unfortunately I need to keep the evap system intact for emissions. A good friend of mine has gutted the entire fuel system out of his NB and now as a "spare" main line in his pile o parts. O lucky day for me

 

Fedex is taking their sweet f'ing time delivering this thing. Now tracking shows delivery by thursday, which kind of puts a hold on my clutch install too.

I'll update by the weekend.

 

Part arrived yesterday, I did a test fit/hookup on it last night and mounted it this evening. No test drive yet.
The hose coming off the rail runs along the intake manifold and into the side of the afpr, the 1/4" hose on the bottom is the return and runs to the evap line. Adjust base pressure on top and depending on if you want a 1:1 increase with boost, attach a vac hose and find a tap on the manifold.




Well, that's about it for this one, I'm out of pictures. I'll update again once I get the tune fixed and then the fm2 goes in.

 

So I got in a good few hours of tuning today, and it's getting much better already. First time out, I set the base pressure to 60 on the afpr, which is pretty close to stock and had the na fpr hooked to vacuum and the afpr detached from vacuum. I'm not sure if the old fpr is a 1:1 or not, but but it ran rich in cruise (11.5-12:1) and boost onset was 10.5:1. I messed with the emb injector correction chart and got it a little better, but still had the flat spot entering boost.

Then I tried running vacuum to the afpr and the fpr, this should give me a max pressure of 70psi@10lbs boost and after tweaking the inj. correction on the emb it seemed to run even better, and I was seeing a bit leaner in cruise 13:1 and 11:1 in boost at 10psi where before I was tuned for 12:1. The dead spot was still there on the onset so I made my first adjustments to the fuel map and pulled some fuel in vac/cruise and right at 0 psi. That seemed to help with the bogging in boost onset.

Then I upped the boost to 14 psi and before I would see the AF climb to 12.5:1 by redline I was seeing 11.5-12:1

I need to add additional cells to my timing and fuel maps because I'm tuned for 15 psi max. Once I get around to making a new map, I'm going to try for 18 psi.

Believe it or not, my clutch that was fried at the dragstrip was actually holding the power ok all day. I think the 1st gear launches are what kill it. Oh well, the new one will be in soon enough.

 

I wonder if its possible to reuse the factory plastic fittings and fuel line? It looks like the fittings are just pressed into the lines, might make it easier if you could scavenge them off something.

Of course, I would hate to take chances with something like the fuel system.

 

I got mine from oriellys dorman part #800-081.5. It was a pack of 5 for 13$.
I like to keep OEM parts reuse able just in case.

 

I need to find a stock looking 1:1 vacuum referenced regulator that'll do 60+psi, or I need ti figure out where to stash an aftermarket one out of sight in the engine compartment. Humm...

 

You know, I was tempted to try bolting the stock 60psi reg onto the rail in place of the pulse dampener instead of using the NA one. It would bolt right on but I don't think it would fit once the plenum was back on, plus its not vac referenced.

From what I understand, even though the na is a 3 bar, as long as the afpr is after it and set to a higher base pressure, the na will basically stay full open the whole time.


I got my afpr off of eBay and only paid $25 for it. So far so good.

 

I had the same thought, though I'm not sure I want to deal with 2 regulators in series like that. Someone had posted a link to some sort of aluminum adapter block that you could bolt a stock FPR to and then have NPT or AN fittings attached, but now I can't find the damn post. I need the stock regulator for the stock injectors and ECU, but I don't mind swapping out regulators if I'm already swapping out injectors at the same time. My deal is that it just needs to look like it belongs there so purple anodized regulators with gauges need not apply

My 650cc FIC injectors @ 3bar are going to flow more fuel than I'll ever use with my little BP. It would be super convenient to be able to swap in a NA FPR when the EV14s are installed.

 

At I.L. motorsport you can buy the European 1.9 return style fuel pressure regulators:

Quite pricey but they fit the correct way round...

Kraftstoff Druckregler Original

Btw. I.L. also has an English site.

 

Bitchin, thanks for the link. Here it is in English because my German is ****: Fuel Pressure Regulator Genuine.

I do have a square top, I'm wondering if I could get that to fit on a M-Tuned rail, or even better, an OEM euto rail. Any way you can confirm that the EUDM 98-00 NB is actually 60psi?

 

Ok, that's $116.19 USD with the current exchange rate, $138.44 if I get boned with VAT. This of course does not include shipping from Deutschland.

Any of you euro-bros want to find me a rail and regulator from a 98-00 1.8 (1.9 lol?) NB in a wrecking yard? I'd be more than happy to give this a try if I can get some help finding parts.