wopa20

Just pulled my fuel rail and the screw and washer was sitting in the plastic cap for the pulsation Dampener, Can I screw it back in? Car has 15000miles

djSL

iTrader: (5)

No. If your FPD is broken or suspected to be broken, replace it! It's infamous for causing engine fires.

Assuming S4, you can either replace it with OEM or delete it entirely with a banjo bolt. Here's a link to some information on why and how:

FC3S Pro v2.0: FAQ - Pulsation Damper

Rotary Alkymist

Don't delete it, just replace it. Without boring why you should keep it just remember that the 787B was equipped with a pulsation damper and an OMP. It's there for a good reason.

ATexRex

Interesting, I've been out of the game for over a decade, but common advice back then was banjo bolts.

I went with a new PD myself.

gsmithrx7

They only last for a few years at best, and do you want to buy a new one for $150 every couple of years? Running the risk of a diaphragm failure with a possible engine fire? A new one could fail!
The service manual used in Australia for RX-7's stated that the purpose of the pulsation damper was to lessen the noise made by the fuel injectors! Nothing to do with smoothing out the fuel pressure at the injectors made from the pulses of the fuel pump! Do fuel pumps pulsate, I figured they were rotary type pumps? What do I know!

If their purpose is to quite engine noise, yes they will appear on every car. But I would be interested in how they are designed, the engineers would have to know the early designs could leak. Do the newer ones have a safer design?

I have been running a banjo bolt in place of the damper without any issues! Injectors running great, no problems. I thought they were leaking due to a flooding problem but they came back from the rehab shop stating they were not leaking! It was a loss of compression in the engine.

Rotary Alkymist

Mine is 35 years old and it works fine. Do you think the Mazda racing team was worried about fuel injector noise?

Edit: 89 is the year they finally upgraded their design and they are not known to fail often.

gsmithrx7

The race team just went the easy route rather than reinvent the wheel!

If it is there for a real fuel pulsation absorption reason, I would love to hear about it.

Rotary Alkymist

A rotary engine needs twice the delivery speed because injectors are firing every revolution. With the injectors opening that quickly the pulses change the pressure during a fuel delivery event. Keeping it simple the pulsation damper does exactly what its name describes, it dampens this effect and improves fuel delivery, more even and precise.

People say that aftermarket fuel regulators have dampening capabilities. This is an incorrect solution as the damper is located before the injectors.

Fuel delivery at 8000rpm at 15psi calls for precise delivery and those pulses will effect what an injector can deliver for that particular event.

Is it necessary? No. Does is help to delivery fuel more accurately? The answer is yes.

Remember, these events are so close to each other that those pulses effect following events.

gsmithrx7

Again, I need an automotive engineer to weigh in on this subject. To smooth out the fuel deliverery at WOT. For what benefit? The fuel injector cycle is computer controlled, I think the computer will do a better job of delivering the best amount of fuel at a given instance then the pulsation damper can do. The pulsation damper is an analog device, its only purpose is to absorb the fuel injector cycle pulses and quite them! They are on every fuel injected vehicle because of their ability to subdue the clicking of the injectors. Anything to do with engine noise while you are driving the vehicle is very important to it's sale! I have a fiberglass pad on the underside of my hood who's only function is to keep the engine noise down!

I have a 35-year-old pulsation damper that the screw has not backed out of, who out there would install it on their engine? No one, if it fails and sprays gas all over the engine maybe you will notice it. If not, flame on! Not worth the trouble!

Anything that is detrimental to keeping these cars running is not worth it! Ohh... it stock, I must keep it! Yeah, if you don't drive it! If you really want to have a pulsation damper, find one that does not fail!

Rotary Alkymist

You seem to have it all figured out. Did an engineer tell you that? LOL. '89 and up don't have a screw for your information.

Anyway I just explained the function of the PULSATION DAMPER. It's not my fault your don't understand physics. Your ECU cannot compensate for differences in pressure. Where the hell are you coming up with this ****?

Put a banjo on and "you'll" be fine.

Edit: This is where you get mad and write a page.

Rotary Alkymist

Mazda Race Team "I think we should put a catalytic on the exhaust to quieten the noise on the track at 9500 rpm. We might shave a couple of seconds"

Mazda Race Team " I don't know about those injectors, they're pretty loud, I think it's the fuel pulsation causing all that noise, especially now that we have a cat on the exhaust. That clicking is really annoying the driver".

Are you listening to yourself?

gsmithrx7

Let's talk about racing, I am not savey to anything to do with racing! I would like to be a fly on the wall as the racing engineers built these 787 engines. What was the top end doing with the fuel delivery? At racing speeds, with top-of-the-line fuel injection equipment, why put a potential fuel leak problem in the system? What year are we talking about? The updated damper has fixed this problem, if they used this updated version I would be interested as to the overall benefit of absorbing the pulsations of the injectors. Smoother fuel delivery at the tip of the injector, by the time the air/fuel mixture get through the intake manifold into the rotor intake area those bouncy pulsations would be of no consequence. We need to see a dyno run with and without the pulsation damper to really see if there is a real benefit to running with a damper in a race car!

Oh, I listen to myself, I'm the only person who makes sense to me!

Rotary Alkymist

Your logic is inverted. The part is there to eliminate a problem. I don't think you have the capacity to grasp fluid dynamics enough to understand the function of a pulsation damper. This isn't for you and you're too lazy to research things yourself so I guess you're fucked LOL. The fun just ended.

gsmithrx7

Now we are getting somewhere, you are quick to use a broad area of science to vindicate your claims about dampening the fuel injector cycles, you say smoother more even flow from the injector tips. At WOT racing speed, the duty cycle has to be close to 100%, that has to be micro-seconds between pulsation! I can do the lazy *** research, my step-son is a mechanical engineer, let's get his input. Since Pratt &Whitney listens to his fixes for their jet engines, he might know about fluid dynamics.

My reasoning for the existence of pulsation dampers is that they are used to quite the clicking of the fuel injectors. Less noise in the passenger compartment, the better! Your claim about smoother fuel delivery into the air stream based on fluid dynamics is possible but NOT the main reason for them to be on all fuel injection systems today.

What detrimental problems occur when you do not absorb these pulses? Reduction in power output? Lack of response to throttle input? Fuel injector wear? Please weigh in if you can tell me a reasonable reason for them to be used!

I understand that automobile systems are quite complex and that the average dealer mechanic goes to specialized training to be able to repair problems. But they are not experts, so they are given instructions that they go by. We as enthusiasts go to the manuals, then reach out to forums like this to find out what is what. Your replies are ALL appreciated.

I have a 35 year old pulsation damper with the screw still in place, would anyone use this on their RX-7? I don't think so. If your damper is over 4 years old please replace it with a newer design that does not leak fuel ever! Banjo bolt replacment, never have to worry about a fuel leak but .......

WondrousBread

I also used to worry a lot more about the damper, but awhile back I saw this:


This isn't as conclusive as a real study on the topic, but it's good enough for me to accept that the main reason for the damper is noise reduction.

That being said... I would still never delete the damper in a forced-induction application. It's currently deleted on my S4 NA and I have not seen or noticed any difference in operation. However, there is always the possibility of a transient lean-spike being caused by low pressure at the injector because of the pulsation. On an NA engine this would have no serious impact, but it could be a lot more serious if it causes detonation on a Turbo II engine. In that case I would absolutely run a new OEM pulsation damper, or convert to an aftermarket pressure-regulator which incorporates the damper into it's design.

A $150 damper (or $150 regulator) is cheap compared to an engine, and more importantly, peace-of-mind. I like saving money as much as the next guy. Probably more, since at present I can see the driveshaft spinning through the hole where my shifter boots should be. But I don't think any amount of money is worth having the possibility of engine failure in the back of your mind whenever you're driving.

SupraOfDoom

I deleted mine. I'd rather have the car squirt fuel less accurately than an engine fire.

Rotary Alkymist

No my replies aren't appreciated and you won't be getting any more from me. Your questions have been answered adequately... there's a word for guys like you... I just can't remember it right now. Benighted maybe, or willfully ignorant.

You're most likely a troll of sorts. You have a step-son who's an engineer? How convenient. Typical filler. Have fun wasting everyone's time.

gsmithrx7

This page is my vindication, if there is a valid reason other than suppressing fuel injector noise, I want to hear it. Just because you feel it does this, or I think it does that does not make it factual. Even with physical proof of something, I end up coming to the wrong conclusions!

WondrousBread

Well like I said in my post, I don't think it's an open-and-shut case that the FPD is only there to reduce noise. Clearly that's the primary function, or at least the one that Mazda was concerned with, but I think the case that it could cause a lean injection event under certain conditions is credible. And "credible" is enough for me to not go without one on a forced-induction engine.

I'm not out to convert you or anyone else; If someone thinks they should delete their FPD then they should do it. I'm just providing my perspective, having seen 100 of these threads before.

j9fd3s

iTrader: (3)

Further reading, it can be a big problem https://www.rx7club.com/single-turbo...tions-1090373/

professionalpyroman

Masters and Ph.D. Engineer here, been following this thead for a few days trying to figure out how to best describe what's going on.

Short answer: The engine will run with the banjo bolt damper delete. This will come at the cost of fuel delivery consistency from the injectors. Like WondrousBread said, I certainly wouldn't advise it on a Turbo engine either as you increase risk of detonation events.

Long answer: Before I get into the meat and potatoes here, there are some misconceptions that need to be addressed. The first misconception, or rather misunderstanding, is regarding the "sounds" in the fuel system. It's easy to interpret this as it was meant to quiet down the noise the injectors make, however that is incorrect. If it were simply for the audible pleasure of the passengers, that would be like trying to quiet crickets in a railyard. The engine is much louder than the injectors. One of the old-school ways of listening to fuel injectors was to use a long screwdriver between your ear and the injector to hear it clicking. If an injector is loud enough you hear it clacking around, it's time to replace it.

The second misconception is regarding the information in our service manuals. While they are very comprehensive, we have learned a few things that aren't quite consistent. For instance, the vacuum diagram illustration for the S5 TII has some inaccuracies regarding the LIM. We need to look at the information given to us and ensure it makes sense. For the manual citation by WondrousBread, the caption says that the damper quiets pulsation sounds. This gives the impression, same as above, that it's about what you hear. However, sounds travel through different materials at different speeds, and thereby different frequencies, which I will describe next.

Now for some foundational knowledge. Sound travels at different speeds through various materials primarily dependent on the density of the material. As a general rule, the more dense a material is, the faster the speed of sound in that material. For air, the rule of thumb is around 1000ft/s, for liquids, around 4500ft/s, and for solids, a whopping 18000ft/s (ballpark). You will recall from your earth-science classes that seismographs are used to detect sound waves in rock. Humans can't hear or feel the majority of seismic pressure pulses because they typically occur at very high frequencies. However, sometimes these seismic waves stack and produce large vibrations that actually result in movement. We use this knowledge to our advantage in the rock-blasting world to allow us to blast rock without disturbing existing buildings, pipelines, etc. Sound waves in liquids have some similar properties.

Sound waves in liquids are simply pressure pulses that propogate through liquid media. This is the "noise" mentioned in the manual. In keeping with the increase in speed of sound vs air, there is a general increase in frequency for the associated pressure pulses. Yes, you can have longer wavelength events, but that is outside the scope of this discussion. According to Engineering Toolbox, speed of sound in petroleum is around 4360ft/s. This does make these events occur in the lower millisecond to microsecond range. How does this apply to what's going on in our fuel systems?

Practical application
We have two fuel rails filed with fuel, connected with a hose. These rails are pressurized by the fuel pump, and that overall fuel pressure is controlled by the regulator. The next question is why doesn't the fuel pressure regulator control the "noise" in the fuel system? Basic engineering courses can be summed up by "everything is a spring." With this in mind, lets limit our scope of the fuel system now to the distance between the fuel damper and fuel regulator. Fuel enters the primary rail (on my Turbo II at least) next to the fpd and exits the system either through the fpr, or through the injectors. With our spring example, the fpr establishes the length and spring constant of our imaginary spring. If the injectors weren't firing, the spring would remain relatively undisturbed. When an injector fires, there is a tiny initial pressure increase local to the injector from the solenoid moving up to allow fuel to flow, followed by a pressure drop from the fuel flowing from the injector, and then concluded by a pressure spike as the momentum of the flowing fuel is stopped suddenly with the solenoid closing. This energy input is like plucking our spring. Now the spring will start to vibrate, with pressure waves traveling to each end of the spring, reflecting, and returning until that energy has been absorbed. If you look at a spring vibrating in this way, you will find maxima, minima, and zero nodes, similar to a plucked guitar string. Like a guitar string, different frequency inputs cause different locations of these nodes. Every time there is an injector firing event, there is the associated pressure event in the fuel rails. The fuel pulsation damper absorbs these events and limits the amount of reflected sound, noise, pressure. This not only changes the overall maximum and minimum pressures encountered in the fuel rail, but spreads out the wavelengths so that the pressure pulses cannot stack as easily (prevents resonance). The fpd does this independent of the fpr, as it is acting within the length of our fuel rails.

Why would you be concerned about stacking pressure events, positive or negative? Back to our rock blasting analogy, we use the timing of each blast hole to prevent stacking of pressure pulses that would destroy nearby buildings, etc. In the case of our fuel systems, there are a few adverse effects to not managing pressure pulses. If you have a stacking pressure event over an injector, you can have some adverse effects. Lets first talk about the fuel delivery consistency aspect of this application.

The pressure of fuel delivery is important for consistent performance of the fuel injectors at the nozzle. The reason we have pressure regulators is so that as the injector cycles increase, there is enough fuel to support those low-pressure high-flow events. There is an acceptable range of pressures for a given fuel demand during normal operation. The fpd smooths out the pressure pulses in the fuel rail so a more consistent pressure is maintained within and across the fuel rails. This is to maintain a consistent shape of the fuel injected into the manifold, as mentioned previously in this thread. How does that factor into normal operation? If you are using the stock injectors with the diffusers in the LIM, you need to maintain a straight jet of fuel so it lands on the diffuser and atomizes for the intake stroke. If the local fuel pressure is too low, you will get less of a squirt and more of a dribble. This will make a slower moving blob of fuel, instead of a jet of fuel. This blob does not diffuse as well, and might be blown astray by the airflow in the intake so that some of the fuel is wetted against the walls of the intake rather than atomized. If the local pressure is too high, it will put more force on the injector solenoid and slow the opening of the solenoid, shortening the fuel delivery event. Even if you are using injectors like RC Engineering that diffuse the fuel into the intake runners without necessarily needing the diffuser plates, you still need them to cycle as the ECU designates.
At the far extremes, you could have stacking pressure events that could be so severe as to prevent the injector from opening, or miss delivering fuel for a cycle. Not likely, but could happen in combination with other issues. We are still talking about acoustic events, not getting into cavitation, or supersonic pressure events. As far as effect on general operations, not managing pulsations can increase injector wear, and affect fuel delivery, especially at higher rpm. This would affect fuel efficiency/power at higher rpms as well as increase engine vibration from uneven firing events. For the majority of puttering around, its not going to effect anything. However in higher rpm or transient fuel demand events "spirited driving", you can have serious issues if you don't address it. This doesn't affect engines at lower rpms, because the pressure events are spread out.

I hope this addresses some of the points brought up and provides a better understanding. If you still want to reduce audible noise from your fuel rails, you can use a rubber block to absorb that, but the fpd performs a different function.

peejay

The stock rubber fuel lines make an excellent pulsation damper all by themselves.

Doing something because a racing vehicle does it is crazy.

They also ran an MOP because fuel economy is the name of the game for 24 hour racing with a fuel quantity limit, if you inject the oil then you can run deceleration fuel cutoff. If you are not running DCFO in your fuel injection scheme you can safely premix.

​​​​​​

Rotary Alkymist

I will momentarily digress.

What is lubricating your housing during deceleration if you're not running the pump? The answer to that is nothing is lubricating during deceleration when running premix only. This alone is a good enough reason to run the pump. An overhaul at 50,000km would prove the benefits.

I'm not saying do it because it's on a racing car, I'm merely pointing out that for it to be on an engine made to race or track, an engine with millions in r&d put into it, one could logically( or so I thought, I expect too much sometimes, I'm told that often) assume that every part has a very necessary function and with performance being priority.

Why do you think the pump offered better fuel economy? Because the pump makes more efficient use of the gasoline probably due to the couple lbs of compression you gain from the oil injection. It also helps to reduce engine temperatures.

I'm not sure how hard you run your car. I run my car hard. I had the displeasure of having OMP issues and I drove without it for a bit. Engine temps would fluctuate way more without it. When pushing hard on a hot day you can reach dangerous temperatures.

I will never run my precious rx7 without it ever again. It's necessary for longevity and most importantly "endurance". You can literally hear the engine quieten with oil injection. It's audibly apparent.

Rotary Alkymist

This is simply untrue.

peejay

People have been eliminating the damper since time immemorial. They have been failing since the 12A Turbos and GSL-SE engines. They have been causing cars to burn to the ground since the mid 80s. Eliminating it is a safety measure.

I have not run one since 2008. in the real world, it isn't an issue.

If you want to be completely **** retentive about it, use a banjo bolt and install one or two inline pulsation dampers from any EJ engine equipped Subaru. They are mounted in the fuel line near the left side strut tower and are extremely swappable. Note that Subaru stopped using them after a while, too, but at least they are sealed units that won't spray fuel out under pressure.

Off topic, I explained why the MOP allowed better fuel economy. It allowed them to have deceleration fuel cutoff. I am uncertain if LeMans required a spec fuel that would have prevented them from premixing, but even if they did, saving fuel was of major importance. IIRC they were also running around 1.1-1.2 lambda at WOT.

I do not have racing rules with respect to fuel, so my 10,000rpm 13B gets 60:1 premix and no MOP (with steel seals) and my 12A has a MOP and gets 120:1 premix to protect its priceless rotor housings. Neither has DCFO. I tend to get about 100,000km from an engine before the side seals are worn out.