Inconsistent fuel pressure & Radium pulse damper
 

OK, so as documented in my build thread (https://www.miataturbo.net/build-thr...5/), I've recently converted my 99 from the stock NB pressure regulator setup to use an FM "BFK". AEM regulator mounted where the filter normally goes, -6 AN lines, deleting the fender-mounted pulse damper. Walbro pump, older FM dual-port rail, ID1000s, MS3.

With the stock regulator & pulse damper, the Walbro was overwhelming the FPR at idle, but under boost the injectors leaked enough that it worked well. Logging the fuel pressure, the stock system kept it between 60 and 61 psi.

With the AEM, I now have a reasonable idle fuel pressure (plus I can vacuum reference it), but it's giving me very noisy fuel under boost, wavering by 15 psi at 270 kpa MAP (white trace in graph #3):

https://www.miataturbo.net/attachmen...ine=1435618104

So I'm thinking I need a pulse damper again. I've still got the rail mounted one, but the fender mounted one would need a bunch of fittings and adapters to go into the AN lines, plus it's 5/16 rather than the -6 AN lines. So poking around on the net I found this:

https://www.radiumauto.com/Blog/Post...lse-Dampers-90

Anyone know anything about it?

--Ian

Question: When you logged the stock system, was your wiring and fuel pressure sensor the same? Just to rule out noise affecting the readings.

Same sensor, same sensor wiring. Different plumbing, obviously. :)

--Ian

Hmmm. Now I'm gonna go look, I don't remember seeing a damper on my fuel rail, it's a 2003 fuel rail though, let me check. I know I had a fender one and it's gone now.

Also given the fact that you're running 1,000 cc injectors, I'm sure some pressure drop is going to be unavoidable but I guess the damper would still help.

Are you using the dual port functionality of the rail? I run a stock rail and it's single feed. I wonder if your experience would change by feeding it only from one end? I dunno how easy or difficult that would be for your to test.

IIRC, the rationale for using double-ended fuel rails is that by supplying both ends it cuts down on pressure inconsistencies going down the length of the rail. Speculating at random, I would think a single-ended rail would increase the communication time between a rear-mounted regulator and the furthest point of the fuel system, thus making it less consistent.

I'm "using" the dual port functionality in the sense that it's hooked up at both ends. There's a -6 AN line coming forward from the tank, and in the vicinity of the intake manifold it goes into a tee with a line that feeds the pressure sensor. The other outlet of the tee is attached to a second tee that then has lines feeding each end of the rail.

The rail looks like this:

https://www.miataturbo.net/attachmen...ine=1435620255

The elbows on each end are the two feed lines. The pulse damper is mounted underneath, in the center, and isn't visible.

The tee fittings look like this:

https://www.miataturbo.net/attachmen...ine=1435620255

The feed line is the one with the straight, blue hose end and the the plastic ribbing covering up the braided line. The right-angle fitting at the top of the photo goes to the sensor. The silver tee at the bottom goes to the two feed lines which branch off right and left.

--Ian

<p></p><p>On the 2003 fuel rail the damper is where the regulator is on NA cars.</p>

The AEM regulator has known issues in the Honda community, I'm sure the form and function of your regulator is similar. I have never owned an AEM regulator so I cannot comment on the quality or issues.

In an idealsystem you would have the regulator plumbed AFTER the fuel rail, I believe the dual feed rails is a step down and still acts as a dead end rather than a true regulated system.

Do you know what the issues that the Honda community encounters are?

--Ian

Imagine the carb is your fuel rail


https://www.miataturbo.net/attachmen...ine=1435622441

The AEM universal regulator is a 3-port regulator, it is designed to be used in the fashion labelled as "incorrect" in that diagram.

--Ian

From what I have been told the diaphrams can fail prematurely and the springs have been known to lose tension and not operate in a linear fashion.

Cap one end, it's universal so it's made to fit a dual rail engine as well. Think about how a regulator works and it will make sense.

Neither of these is likely to be the cause of the noisy fuel pressure that I graphed.

As for the routing, yes, the FPR could be used as a 2-port regulator if desired, but it is specifically designed to be capable of being used as a 3-port regulator as well.

--Ian

If your fine regulating the pressure at the line and not the rail expect problems. Your not using the regulator properly, I don't care how many ports it has.... Or how many dampers your using.

He does have a point- the regulator that regulates pressure WOULD work better the closer you can get it to the fuel injectors. I'm not saying it's the cause of your spikes, it's probably not, but it would regulate and dampen better being closer. I never liked where FM put the regulator in their fuel kit. I guess it makes for an easy install but not ideal.

Mazda puts it there and the pressure stays within 1 psi of the set point.

--Ian

Here's a datalog of the factory regulator, with the range on the fuel pressure forced to the same delimiters as the ones in the previous image. Once again it's the white line in the 3rd graph, look at the part where it's in boost, in the center under the plateau of the duty cycle.

https://www.miataturbo.net/attachmen...ine=1435643893

Yes, it's moving around outside of that range, that's because the Walbro pump is overwhelming the factory regulator, which is the whole reason I put in the AEM.

--Ian

I would at least try moving the regulator to the correct spot. That's absolutely not how that's supposed to be used, and that's definitely not how the Mazda return systems works. :)

I don't use a pulsation damper on the MX6 and don't have these problems. My regulator is mounted "after" the rail, though. I do run upwards of 80psi rail pressure at full boost.

The factory system is a well engineered SYSTEM designed to work well within its parameters, not various off the shelf parts thrown together and expected to work.

Mazda put the fuel regulator where they did to meet EPA standards, it was not a performance minded change.

It looks to me that the difference between the 2 is that the "incorrect" version will regulate pressure at the outlet of the FPR; the pressure at the rail will be the pressure at the FPR minus the pressure drop in the line from the FPR to the rail.

This pressure drop will be proportional to flow (power) and inversely with the size of the line. If the line is big, then the pressure drop will be small. This pressure drop characteristic will be consistent for a given line, and will be baked into the fuel table during tuning.

I don't see how the "correct" version will reduce pressure spikes in the line, unless the FPR can absorb them (i.e. act like a damper), and is mounted close to the fuel rail (in either the "correct" or "incorrect" version).

I always wondered if rubber lines would damp pulses better than SS braided teflon lines like the above.

BTW so the factory setup uses a 2nd damper near the fuel tank?

Interesting that pulse dampers have an operating pressure range. Looks like they bottom out at some pressure.

Ian, how hard would it be to put a factory fuel rail back in? I wonder if the small damper on the end of the rail is enough.

<p>He already ordered the Radium unit. I assume he will update here when he gets it</p><p>&nbsp;</p>

The AEM is "supposed" to be used this way, that's why AEM built it with three holes. They sell a two hole version as well, if they didn't intend for you to use it to regulate a dead-end setup like this then they wouldn't bother to make it.

Moving the regulator to the "correct" spot would require buying about $200 in new AN hoses and fittings. The FM-supplied hoses are pre-made lines with non-rebuildable hose ends on them, so I'd have to throw out every line I already have. It's not a cheap experiment. EPA requirement or not, pretty much every non-DI car on the market for the last decade does the fuel pressure regulation this way, and they all made it work.

Jason: The theory is that mounting the regulator on the rail should reduce the pressure spikes because there's less lag between the regulator and the injectors. The -6 AN hose is intended for fuel, and is rubber inside. Teflon lines are usually -3 or -4 and used for brake fluid, I think.

concealer: Have you actually datalogged your fuel pressure?

Savington: I don't have the factory rail any more, but the small factory pulse damper is present, mounted on the underside of the FM fuel rail (not visible in the photo). The one that's missing is the one that mounts on the fender, next to the intake manifold. Radium's blog entry comments that pulse dampers are tuned for specific pressures, and since I'm now using a manifold-referenced regulator instead of the factory 60 psi, that may be why it's inadequate. The Radium dampers are vacuum-referenced as well, presumably to try to address this.

The Radium blog entry about their pulse dampers describes pretty much exactly the problem I'm having, so I decided to go ahead and order one to give it a try. We'll see what happens.

--Ian

It has three holes to be used with 2 rails, at least that's what i've always done if using both sides. Maybe i've been operating under the wrong information my entire "career." Single rail, i've only ever used one on the side, and the bottom return. Plugged the other. Two rails, use both ports.


I haven't datalogged my fuel pressure, i don't have that capability, the car doesn't even have a standalone. You're talking about big swings, though, i'd see some weirdness on the gauge or wideband, and i'm not.

Admittedly, i don't mess with newer cars much, but i've never seen an OEM feed through an FPR.

Anyways, i hope this damper solves your problems. We could all maybe learn something. :)

Yes, the amplitude of the pulses is high, but so is the frequency and I wouldn't be surprised if an analog gauge has enough damping in it to not show them. The cheap analog gauge that I have attached to my AEM underneath the car doesn't show the pulses at idle (I dunno if it does under boost -- I haven't tried riding underneath the car to check! :) ).

The wideband isn't going to tell you if an individual cylinder is lean unless you have individual sensors per cylinder and even then I'm not sure if it's got enough resolution to pick out the results of a single cycle.

--Ian

It's an electric sender, but you may be right.

<p>I've not used the Radium damper, but have used their other products.&nbsp; Everything Radium branded I've touched or seen has been very high quality.&nbsp; However...I agree with the newb.&nbsp; Plug the 3rd port and run a return from the rail to the regulator.&nbsp; This will make the FPR regulatre pressure in the rail instead of pressure at the FPR outlet.&nbsp;&nbsp;</p>

<p>Stock NB fuel pressure target is 60 psi. I'm running an Aeromotive 340 at 60 psi, stock NB fuel system otherwise.</p><p>Sounds a little extreme.&nbsp; Disconnect the FPR and join the inlet and outlet hoses with a union. Remvoe the 2nd tee fitting, single feed the rail, extend the other feed back to the regulator. If you want to get fancy, you might be able to leave the dual feed and pull your return from where the damper currently resides.&nbsp;</p><p>I've seen this problem before, fixed it before in the same manner (not in a Miata, however).<br />&nbsp;</p>

In theory they would as they reduce fluid hammer by their springyness.

Come to think of it, a device that has a rubber diaphram (hose) and a spring (nylon braiding) where one side has fuel on it, the other doesn't, could be used to dampen vibrations??? Would just need to install it inline with between the injectors and the regulator. Hmm....

The spec is 57-61, with the Walbro and the stock FPR mine ran about 68 at idle, 61 when under boost.

I have one 84" line, 2 24" lines, and 2 18" lines. Converting to a return system with the regulator mounted up by the rail requires 2 lines of about 100 inches each. I could buy 5 -6 AN male-male unions and make a long hose out of all the short ones, but I'd still be about 3 feet short of the total length of hose I'd need, plus most of those hoses have a right-angle on one end, so stringing them together is going to be really awkward.

The damper mount is probably too small in diameter to serve as a return line.

And yes, rubber hoses act as mild dampers. Braided stainless lines are rubber hoses with stainless armor over them, they stretch the same small amount as non-braided rubber lines do.

--Ian

Interested to see if the pulse damper fixes your problems. Where are you going to install it.
<br />
<br />If the damper mount is the same as the fpr mount there are adapters that mate to an6.

Yeah, there are adapters, but would still be a restriction compared to a -6 line because it's smaller than 3/8. I'm also not sure if there's room underneath the center of the rail, the line would have to feed out between the fuel injectors and the intake runners.

For my initial test, I'll stick the Radium damper between the tee and one of the feed lines. It's an easy place to put it because I can just unscrew a couple lines and put it in the middle, and it's roughly in the location where the factory fender-mounted damper went. I'll get fancier if it's necessary.

--Ian

I don't think so. Isn't braided stainless stiffer than the air around a rubber hose? It has to be! That is how they can withstand several thousand PSI without bursting.

Anyways good luck, I do hope you get this fixed. It's an odd problem for sure. From an engineering standpoint the system is underdamped, and I think regular rubber hose would help dampen, thus reduce the spikes. But honestly moving the regulator or doing what Ben said with the lines are two other possible solutions, or adding another damper somewhere else. Any of those should help.

One thought, the OEM system (with its two dampers) has very rigid lines from the factory, they're steel tubing and plastic hoses that don't seem to flex much.

Hm. I was once told that the steel braiding on AN lines doesn't actually make them stronger, just more resistant to damage. OTOH, you may be right about the higher pressure rating, I don't know.

The Radium FPD should be here tomorrow, we'll see how it goes.

--Ian

Yeah from what I've seen, fuel hose for say a carborator is just rubber or rubber with 1 layer of nylon braiding. As you step up to say fuel injection hose, it has a few layers of nylon braiding for added strength, and the rated pressure/burst pressure goes up. Hydraulic hoses have braided steel in the hose, either inside or external or even both, but they all have it from what I've seen as the rated pressure and burst pressure has to be pretty high for hydraulics since fluid hammer is a real thing. If you've ever used any hydraulic machine with manual controls, if you quickly actuate and then shut a control, you'll see the hydraulic hoses "jump" from the energy/pressure spike.

I worked around high powered hydraulic machines at my previous job, saw a lot of this...

Cool looking forward to see how the new damper works! I actually have a fuel pressure sensor for my car I need to install. After seeing your data I'm curious what my own car is doing now!

But it has a 2nd damper near the fender, which Ian removed.

I guess swapping fittings around sucks. But it is funny that you would remove the factory damper, and then install an aftermarket damper.

I have 6AN lines too. I guess to hook up the factory damper, you'd have to have two of those 5/16 Hardline to 6AN adapters. Hmm... But I saw mentioned here they're tuned for a certain PSI, and mine has a 1:1 reference so maybe the factory damper wouldn't do much at 90 PSI fuel pressure.

The Radium blog post in which they announce their pulse dampers claims that dampers need to be tuned to a specific fuel pressure. Granted, that's part of the story they're telling to convince you to buy their awesome new pulse dampers, but it sounds reasonable.

https://www.radiumauto.com/Blog/Post...lse-Dampers-90

Aluminum AN fittings are expensive. Using the factory regulator in the factory mounting location would need a pair of the push-lock-to-dash-6-AN fittings, which are around $25 apiece. Then to get the hoses onto the mounted-pointing-straight-up inlet and outlet I'd need a couple of 180 degree hose ends (another $20 each). By the time you add all that up, it's only $30 off the price of the Radium unit that's designed to be mounted inline and includes the AN fittings. Assuming it does what it's advertised to do, that $30 is worth to remove the restriction, gain the manifold reference, and have a cleaner overall installation in the end.

--Ian

I would agree, especially if it proves to work as good, or better, than the OEM damper.

I'd say they operate properly within a spec'd operating range, not "tuned". My guess is some kind of expansion chamber bottoms out above that range.

I'm still new to the whole Miata world, But FWIW over in the Evo X world we were facing some fuel pressure abnormalities a little while ago with after market fuel rails and AFPR's, which was exacerbated with larger injectors. around 2000-2200 RPMS, we would dangerously lean out with no real explanation despite having pleanty of pump to support high HP numbers (some guys were running twin 450 pumps and still having the issue). Turns out our OEM FPR's had dampers in them internally and when switching to AFPR's we were unintentionally removing them causing a weird resonance in the fuel rail that couldn't be tuned around. Some guys experimented with the Radium FPD and found it solved all tuning issues related to that 2000-2200 lean spot. The X platform is obviously highly different, as is the fuel system in that it uses a more tradition performance oriented Pump->Rail->FPR->Return setup, but we did have great success with the Radium FPD. We also found a solution to running big pumps at idle/no boost cruising but would still provide full power to the pumps when getting into boost, basically for the same reasons as stated earlier, over whelming the FPR for those running very large pumps (wally 450's in single and twin configurations, twin 320's, etc). It might be worth the little extra expense to swap your regulator to the return side and do the required plumbing, it might make tuning easier as well.

Radium Engineering has added a fuel rail that can use their proprietary products including the better fuel pulse dampers to help smooth fuel delivery.

https://cimg7.ibsrv.net/gimg/www.mia...176e853309.jpg

For what it is worth, I use the FPD-XR matched to manifold pressure with my FM BFFK at 60psi (matched to manifold) with the damper up at the end of the line right before the T for the two rail inlets. I haven't had any issues though I haven't been logging my fuel pressure. Interesting that there's a fuel rail available now though.

Here is a direct link to the fuel rail: Fuel Rail, Mazda MX-5
Looks like a nice piece and price is pretty reasonable at 140 dollars.
Unfortunately if I add the 4 ORB-8 fittings, import tax and shipping it ends up at 300 dollars at my doorstep, but that is still below the price of the Flyin' Miata one.

One thing I do not get: why is the thing not compatible with the '99-'00 USDM VICS manifold? As far as I know the VICS manifold is identical across all markets between '99-'00. We did not get the flattop either until '01.
I guess Radium does not know the rest of the world also had the VICS between '99-'00 or am I missing something here?

My guess would be that they designed the rail for a specific car that had a specific manifold on it and didn't really think about other manifolds until too late. The 99 ViCS manifold has the least clearance of any of the NB manifolds, I think.

For those who might be reading this thread and wondering about the results, I did install the Radium damper and it did work. Results got posted in my build thread, but not cross-posted here. Link:

https://www.miataturbo.net/build-thr...5/#post1250082

--Ian