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