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Discussion Starter · #1 ·
Hello, I am wondering if anyone has experience with fuel pressure pulse dampers. From my understanding, its purpose is to help maintain a more consistent fuel pressure by absorbing the rapid fluctuations created by the injectors opening and closing and rapid changes in load. I never thought this was a huge deal until put a fuel pressure gauge on my K24A2 swapped 04 Civic a few days ago and discovered that the fuel pressure is so bouncy at times that I can't even really read the gauge. It drops quite drastically when snapping the throttle open too or suddenly loading the engine, I'd guess possibly by somewhere around 5-10 PSI but I can't really tell because the gauge is so darn unstable.

Initially I thought the bouncing was just caused by engine vibration, but then I noticed the gauge is almost steady when in decel fuel cutoff (injectors not firing). Although understandably not perfectly steady, the difference in the pressure readings between the injectors firing or not is very obvious. I then started searching for a way to add an OEM pulse damper to hopefully stabilize the pressure a bit and I think I found a way.

For some reason, the K24 used in the Accord and TSX doesn't have a pulse damper on the fuel rail while the K20 in the RSX and the K24 in the CRV does. Doesn't this seem backwards since higher RPM and larger injectors are said to make a pulse damper more necessary? Honda didn't put the pulse damper on the high performance K24A2 which revs to 7200 RPM and has 310 CC injectors, instead they put it on the not particularly high performance CRV engine which revs to only 6500 RPM and has 270 CC injectors. Any ideas why the pulse damper was deemed necessary for some of the K series engines and not others?

Anyways, I found that the 05-06 K24A1 fuel rail looks absolutely identical to my K24A2 fuel rail other than having a pulse damper, so I decided to buy one and do some testing to see how much it actually stabilizes my fuel pressure and report back. I'm pretty sure it will fit, although not yet certain since it hasn't arrived yet and the lower intake manifolds are different. But since worst case scenario I'm only out $30 and a few minutes of my time, it's worth a try. Whether it works out or not, everyone gets to learn something cool and hopefully useful and that's what this site is all about.

Here's the rail used on the CRV K24A1. Note the pulse damper between
injectors 2 and 3 (the round thing).
Automotive exterior Gas Rectangle Auto part Font



Here's the rail used on the K24A2 and K24A4. Note that there is no pulse
damper between injectors 2 and 3 even though it has the half circle looking
spot for it.
Underwater Water Fin Aviation Wood
 

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Lotus Elise K20A2
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High rpm and load is where the pulse damper does the least.
Pulsing happens the most at more like low and medium rpm and decent load. The pulses come in slow, but big. A dead end system has a rather low resonance frequency. If both coincide, you get wild fluctuations. At high rpm everything smooths out. At very low loads or idle, the fuel demand from the short duty cycle is very small and covered by the fuel systems elasticity (from the mostly polymer fuel lines), the damper volume and static pressure.

One of the main drivers of such fuel systems is cost/space savings from running only one fuel line into the engine bay and being able to integrate FPR and pump into one unit.
There can be a small advantage of less fuel heating from a lot of it making a loop through the engine bay.

For most high performance applications, this arrangement is skipped in favor of a proper flow through fuel rail. The 2x line length adds some extra damping and the pressure drop across the fuel rail is smaller. Flow is way less variable across the fuel rail leading to these more uniform pressures.
Once you bigger on injectors, the dead end systems become to non-uniform for good emissions and performance.
 

· Arouse the DAMPFHAMMER!
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On my DAMPFHAMMER engine, which has an highly efficient alternation of load process, I wasn't able to tune it as there were MAP amplitudes of up to 12 kPa, which got transferred into the fuel system. This resulted, recognition thanks to the fastest wideband controller system on the aftermarket (AEM X-series), to lambda oscillation of up to 0.06 points. So the issue was real at intake, at fuel and at the energy transfer system. The whole engine was affected and not tuneable, as the effects lead to a stable but quite annoying responding oscillation in addition: the MAP peak was transferred to the fuel injection timing, which added or cut the amount of fuel injected around an average value, which increased the actual oscillation of fuel pressure in addition. A real mess.

To solve this I had to take measures on hard- and software of every system, to gain both, the ability to keep the efficiency of alternation of load and to improve the tune-ability of the engine. At the fuel system the location of the pulse damper brought an improvement as well as the damping on the SW-side.

Light Font Rectangle Slope Line

  • frequency of around 3.7 Hz
  • MAP oscillation 12 kPa peak to peak, mechanically dampened (stage 1) measured
  • VE oscillation 13 points peak to peak
  • lambda oscillation about 0.07 peak to peak
  • fuel pressure oscillation about 20 kPa peak to peak, factor of 1.72 of FP/MAP caused by fuel injection duration oscillation
The improvements are actually on the level, where the tune-ability is on almost a level of a typical bolts-on engine setup 🥰.
 

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Discussion Starter · #5 ·
High rpm and load is where the pulse damper does the least.
Pulsing happens the most at more like low and medium rpm and decent load. The pulses come in slow, but big. A dead end system has a rather low resonance frequency. If both coincide, you get wild fluctuations. At high rpm everything smooths out. At very low loads or idle, the fuel demand from the short duty cycle is very small and covered by the fuel systems elasticity (from the mostly polymer fuel lines), the damper volume and static pressure.

One of the main drivers of such fuel systems is cost/space savings from running only one fuel line into the engine bay and being able to integrate FPR and pump into one unit.
There can be a small advantage of less fuel heating from a lot of it making a loop through the engine bay.

For most high performance applications, this arrangement is skipped in favor of a proper flow through fuel rail. The 2x line length adds some extra damping and the pressure drop across the fuel rail is smaller. Flow is way less variable across the fuel rail leading to these more uniform pressures.
Once you bigger on injectors, the dead end systems become to non-uniform for good emissions and performance.
Interesting, I didn't know that. It seems like the fuel pressure is pretty stable at full throttle in 5th gear around 2500 rpm, so that makes sense. But at full throttle and higher rpms, the fuel pressure starts getting bouncy again to the point of not being able to accurately read the gauge.

I may end up getting a flow through fuel rail and return line with a regulator at the rail sometime in the future depending on how well the pulse damper, new fuel filter, and larger fuel supply line works out, I'm annoyed by the bouncing fuel pressure and the pressure dropping under load.

My understanding was the main reason returnless fuel systems are used (other than cost of course) was because having one less fuel line and less fuel outside the tank makes complying with accident fuel leakage standards easier, but I could be wrong. I have also read that the reason was because heating the fuel in the tank less results in less evaporation emissions, which would have sense 30+ years ago, but I'm not sure how relevant that reason is today with modern EVAP systems and sealed fuel systems.

How much would a properly implemented flow through fuel rail actually heat the fuel in the tank by? 10 degrees or less? The fuel rail is pretty isolated from the engine heat on the K series, even sitting on little plastic spacers. Running the fuel return through a small transmission oil cooler or something located somewhere protected would probably dissipate much of the heat the fuel picked up in the rail anyways.
 

· Arouse the DAMPFHAMMER!
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It drops quite drastically when snapping the throttle open too or suddenly loading the engine, I'd guess possibly by somewhere around 5-10 PSI but I can't really tell because the gauge is so darn unstable.
What fuel damper is for are pressure oscillations I've showed in the graph of my aboves post. All what the pressure regulator can't compensate, because its valve is to slow. If you lift the throttle quick, we speak about single event, which causes a flow induced pressure lift, which is not as fast as oscillation, induced by a sonic pressure wave. It's pressure gradient is caused by the fuel flow, which is controlled by the pressure regulator. If that reduced to slow the impulse by the still faster flowing fuel mass can gradually increase. A 5-10 psi peak need some time to be build up, for the eye still fast, but in damper times scale maybe slow. I would say the observed issue is related to both, the fuel pressure regulator and the damper, but more on the regulator.

Could you please draw a scheme of your fuel system concepts and the parts you use for it?
 

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Discussion Starter · #7 ·
I am really curious to see if adding a damper will make a difference. If so, I may add one. Please keep us updated on your findings.
Me too. The plan is to upload before and after videos of the fuel pressure (assuming the rail fits of course) to see how much it stabilizes the fuel pressure. I'm hoping the pulse damper in the CRV fuel rail could stabilize the fuel pressure enough to help with tuning and gauge accuracy for future tests I plan to do such as fuel line size.
 

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if your FP fluctuates at high loads in way you can see it in your lambda gauge, it is commonly a sign of insufficient flow/pressure capability of the pump and/or pipes. A few poor flowing fittings is all it might take. It gets even worse if close loop fueling tries to regulate it. It can lead to oscillations from the pump chasing the fuel demand that goes up and down.
Then fuel pumps also age. In many conversations, heck even stock EP3 Type R cars, the fuel pumps are now 20 years old. They lose some of their capability of providing sufficient flow at high pressure.
 

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Discussion Starter · #9 ·
What fuel damper is for are pressure oscillations I've showed in the graph of my aboves post. All what the pressure regulator can't compensate, because its valve is to slow. If you lift the throttle quick, we speak about single event, which causes a flow induced pressure lift, which is not as fast as oscillation, induced by a sonic pressure wave. It's pressure gradient is caused by the fuel flow, which is controlled by the pressure regulator. If that reduced to slow the impulse by the still faster flowing fuel mass can gradually increase. A 5-10 psi peak need some time to be build up, for the eye still fast, but in damper times scale maybe slow. I would say the observed issue is related to both, the fuel pressure regulator and the damper, but more on the regulator.

Could you please draw a scheme of your fuel system concepts and the parts you use for it?
Good to know, makes sense. With the OEM Honda setup having the pressure regulator in the tank, I wouldn't think a momentary drop in pressure when suddenly loading the engine is abnormal since the pressure regulator needs time to react. I'm not happy about the pressure not coming back up to normal under full throttle and higher RPMs and I believe that's why I feel the engine isn't performing quite as well as I should at higher RPMs (which is the whole reason I decided to test the fuel pressure), but of course that has nothing to do with the pulse damper.

At the moment, my plan is simply to install the CRV fuel rail, replace the OEM in tank fuel filter, and replace the heavily rusted stock 1/4 inch fuel pipe under the car with a 3/8 inch stainless steel line and see if the fuel pressure improves.

If fuel pressure is still not satisfactorily, the plan is to possibly get an aftermarket fuel rail with ports on both ends, feed fuel in one end and out the other into an adjustable aftermarket fuel pressure regulator and through a return line back to the tank, and eliminate the pressure regulator in the tank. I'll draw a diagram of the setup I'm thinking of when I get home later tonight.
 

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Discussion Starter · #10 ·
if your FP fluctuates at high loads in way you can see it in your lambda gauge, it is commonly a sign of insufficient flow/pressure capability of the pump and/or pipes. A few poor flowing fittings is all it might take. It gets even worse if close loop fueling tries to regulate it. It can lead to oscillations from the pump chasing the fuel demand that goes up and down.
Then fuel pumps also age. In many conversations, heck even stock EP3 Type R cars, the fuel pumps are now 20 years old. They lose some of their capability of providing sufficient flow at high pressure.
Good points. I think upgrading the stock 1/4 inch fuel feed line to a 3/8 inch will be helpful since the small line was only designed to supply enough fuel to an engine making about 100HP less than my K24A2.

I know the RSX-S fuel pump I'm using was adequate for this engine when it was new since its K20A2 surely doen't have significantly lower fuel demands, but who knows how much of its capacity it lost over time since it's from 2004 and has unknown mileage. Maybe I'd be better off changing the whole unit instead of just the filter, I'm not sure yet.
 

· Arouse the DAMPFHAMMER!
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I'm not happy about the pressure not coming back up to normal under full throttle and higher RPMs and I believe that's why I feel the engine isn't performing quite as well as I should at higher RPMs
Mmmmhhh...you mean the fuel pressure in the fuel line is not constant under different engine speeds and loads? Or to be more precise, you mean the fuel pressure decreases under higher fuel mass flow demand like WOT and higher engine speeds? If so, that would indicate the fuel pump is fitting to fuel flow-pressure requirement your engine has and is too small/weak. What would help for that case is to upgrade the fuel pump for one which has a higher fuel flow flux at rated fuel pressure as the one installed.

Is that pressure regulator referenced to MAP or PA (plenum or atmosphere)?
 

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Discussion Starter · #12 ·
Mmmmhhh...you mean the fuel pressure in the fuel line is not constant under different engine speeds and loads? Or to be more precise, you mean the fuel pressure decreases under higher fuel mass flow demand like WOT and higher engine speeds? If so, that would indicate the fuel pump is fitting to fuel flow-pressure requirement your engine has and is too small/weak. What would help for that case is to upgrade the fuel pump for one which has a higher fuel flow flux at rated fuel pressure as the one installed.

Is that pressure regulator referenced to MAP or PA (plenum or atmosphere)?
Yes, the fuel pressure seems to decrease under heavy load by an average of maybe 5-10 PSI, but I'm not certain about those measurements since the gauge gets so bouncy sometimes. The RSX fuel pump module I used has an integrated regulator which isn't vacuum referenced, it just tries to maintain a constant fuel pressure of around 50 PSI or so. Basically just a stock RSX fuel system except the probably smaller Civic hard line.

Since the pump, filter, and pressure regulator are all in the gas tank, I don't have a way to check pressure at different points such as before the filter, so I'm going to try changing the $60 filter before changing the entire $400+ pump unit. Worst case scenario would be I need to change the whole unit and I end up with an extra filter, which I will need for my other Civic in 20K miles anyways. Even though it's considered a lifetime filter, I change it every 100K miles for piece of mind.
 

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So are you still going to try adding the fuel damper? Can you do that alone so we can see if that really does change anything before you do other things?
 

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Discussion Starter · #14 ·
So are you still going to try adding the fuel damper? Can you do that alone so we can see if that really does change anything before you do other things?
Absolutely, that's the first thing I'm going to do. My new/used damper equipped CRV fuel rail is supposed to be here Monday and the plan is to take a video of the gauge under different conditions (idle, rev, and decel) with the current non damper equipped rail then change to the damper equipped rail and repeat the same tests. If there's any other tests you would like to see, let me know and I'll be happy to try it.

I don't expect to notice any significant differences in how the engine runs either way since it's basically stock and runs great to begin with, but if I do notice any differences I'll be sure to let you know.
 

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Discussion Starter · #15 ·
The results are in. My damper equipped CRV fuel rail has just arrived and as expected it fit perfectly and the cover fits over it fine. The only real difference if the fuel inlet pipe is slightly lower (hence why the gauge is in a slightly different location), but the difference wasn't enough that I had to modify my fuel line setup.

The damper has definitely helped to stabilize the fuel pressure, but the camera didn't pick up the rapid bouncing of the gauge very well, the difference is easier to see in person but still pretty visible in the videos. The gauge is generally much less bouncy with the damper installed and the sudden pressure drop when I tap the gas while cruising or snap the throttle open is less dramatic. I think a lot of the slight bouncing I'm seeing now is simply caused by engine vibration since the gauge obviously isn't completely steady even when in decel fuel cut (injectors not firing).

Here are the videos of the fuel pressure before and after I changed the fuel rail. The first video is the stock TSX fuel rail and the second video is the CRV fuel rail with the damper.

 

· Arouse the DAMPFHAMMER!
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Here are the videos of the fuel pressure before and after I changed the fuel rail. The first video is the stock TSX fuel rail and the second video is the CRV fuel rail with the damper.
Yeap, there is a calm down on the fluctuation of the fuel pressure, that's good. But you still can see the pressure regulator can't follow the tip in transition. To improve that, a bigger one which is nearer located to the fuel line would be needed.
 

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Discussion Starter · #17 ·
Yeap, there is a calm down on the fluctuation of the fuel pressure, that's good. But you still can see the pressure regulator can't follow the tip in transition. To improve that, a bigger one which is nearer located to the fuel line would be needed.
On a returnless fuel system with an in tank pressure regulator, how much of a drop in fuel pressure is expected under load? I wouldn't expect a drop of more than a couple PSI? Now that the gauge isn't so bouncy, I'm seeing that the fuel pressure is dropping from 50-52PSI cruising down to around 40-42 PSI at full throttle in VTEC.

My new in tank fuel filter is supposed to arrive next week, so hopefully that as well as a bigger fuel line helps keep the fuel pressure from dropping so much under load.
 

· Arouse the DAMPFHAMMER!
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I'm seeing that the fuel pressure is dropping from 50-52PSI cruising down to around 40-42 PSI at full throttle in VTEC.
That is likely a chock issue somewhere in the fuel piping (transition) combined with a too weak fuel pump. Solution approach can be found in both, while the upgrade for the later makes more sense for me. Anyway, my first step would be get rid of the intank fuel pressure regulator. The regulator may control pressure at 50 psi at all engine speeds, but the fuel pressure drop can't be seen by the pressure controller if not connected in near of the fuel line location. Increasing the fuel lines makes no real sense if the regulator sits in the tank, mostly the chocking sections are around or in the fuel tank.
 

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Discussion Starter · #19 ·
That is likely a chock issue somewhere in the fuel piping (transition) combined with a too weak fuel pump. Solution approach can be found in both, while the upgrade for the later makes more sense for me. Anyway, my first step would be get rid of the intank fuel pressure regulator. The regulator may control pressure at 50 psi at all engine speeds, but the fuel pressure drop can't be seen by the pressure controller if not connected in near of the fuel line location. Increasing the fuel lines makes no real sense if the regulator sits in the tank, mostly the chocking sections are around or in the fuel tank.
I think the main restriction other than the likely clogged fuel filter is the stock fuel feed line from the tank to the firewall, which is only 1/4 inch outside diameter and very small inside. I would check the pressure at the tank too, but either way it's getting replaced due to rust and I don't have a way to connect a gauge to the OEM style quick connect fittings without buying more fittings, which I don't want to do just for the sake of testing something I will replace anyways. I have had those Civic/RSX fuel sending units apart before and I don't remember seeing anything particularly restrictive looking inside the tank, but I'll definitely look closer when I change the filter shortly.

How significant are the benefits in fuel efficiency, drivability, tuning, etc from upgrading the stock returnless fuel system to a proper flow through fuel rail and return setup with the pressure regulator right after the rail as you suggested? I know the benefits are huge on a boosted engine, but what about on a mostly stock NA engine?
 

· Arouse the DAMPFHAMMER!
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How significant are the benefits in fuel efficiency, drivability, tuning, etc from upgrading the stock returnless fuel system to a proper flow through fuel rail and return setup with the pressure regulator right after the rail as you suggested? I know the benefits are huge on a boosted engine, but what about on a mostly stock NA engine?
Depends on the reference pressure for the FPR, which can be atmoshphere (very significant) or plenum (less significant). But also where your injector duty cycle is actually and maybe with further changes. The less fuel pressure, the higher the duty cycle.
 
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