Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Fuel damper

General Tuning Discussion

Forum Posts



Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads


Hi guys,

I had i very strange problem with my car. After a very long search i found the problem, my tuner didn't had the proper solution. So i was forced to search for myself to avoid a large bill.

I have a Nissan Skyline R33 GTST running a Z32 Nistune ECU.

I had installed a greddy style intake with a 80mm throttle body. Topfeed 875cc Siemens Deka injectors. Fuelab FPR @ 43,5 PSI (3 Bar)

Because of the modifications i went to my tuner, to map the engine. After this i had a very strange problem.

The engine runs perfectly, but @ +/- 3200 rpm the engine was running very lean. And the engine stumbled. Making no power.

My tuner advised to put back the Original 63mm throttlebody and replace the fuel pump. After this the engine was still running very bad @ 3200 rpm.

After that i never went back, and start to search for myself and followed the HP Academy training course. And i learned a fucking lot.

I purchased the NIstune software and a Innovate MTX-L Plus wideband sensor. To see what's happening. Engine is lean @ 3200 rpm. Adjusting the fuelmap didn't help.

I searched for vacuumleaks and performed a smoke test. No leaks were found.

I measured the fuel pressure and it was 43,5 PSI, taking the vacuum pressure in acount.

Checking the new injectors for dirt and defects, nothing found. Resistence was 12 OHM so this looked ok. Injector wiring loom was ok.

The only thing that was strange, was that the FPR was making a hissing/sissing sound @ idle. I don't know if the noise appeared while driving because of the engine noise. When i was @ my tuner to map the engine i already heard the hissing/sissing sound and i asked him if the sound was normal. He said, that this was normal. So i didn't spend much attention to this sound. But it still bothered me.

Because i could't find the problem. I searched in the engine manual to see if there were some other checks i could do. i thought that there could be some sort of pressure/flow spikes in the fuel/rail. When i was looking @ the drawing of the fuelrail/injectors i saw that there was a fuel damper in the fuel return line.

I mounted the Original fueldamper. And what do you think? The hissing/sissing sound of the FPR is gone and the engine runs very smooth @ 3200 rpm. Still a liitle bit lean, but after adjusting the fuelmap, the problem was gone.

After this i asked my tuner how the hell did he mapped my car like this. He said that, he never installs the fueldamper because you don't need it.

I want to know what you guys think about using a fuel damper. In my opinion, after my problems, you need it. Because i only have experience with my own car, i'm curious what you guys think?

I think that there were pressure spikes in the fuelrail caused by the injectors. I don't think it's the fuel pump, because this is a centrifugal pump i don't think that it will cause pressure spikes.



Attached Files

I had this exact problem with two JZ motors. But that was at much lower rpm. 1800-1900rpm. I've tuned a only track car with that slight issue and informed the owner and he was fine leaving it like that as the engine won't see those revs for long at track.

I made one customer install the fuel dampener to his set up as he told me he was going to be street driving the vehicle. Can't imagine how lame it would feel to hit that lean spot every time you are in traffic or at a parking lot or leaving from a red light.

I think personally my opinion, having a lean spot like that at a much higher rpm range where the engine is capable of producing a good amount of torque, personally I wouldn't like that at all. Or on a street driven vehicle.

Radium has really cool fuel dampener adapter for aftermarket fuel systems. I've done research and found that changing fuel lines from oem hardlines to aftermarket steel braided or nylon braided lines will act as a dampener internally as the inside can flex and dampen better than hardlines. Which is why some vehicles that has aftermarket fuel lines from gas tank to engine will be just fine when tuning and not experience this lean issue.

So I wouldn't say every car needs it. But if you come across, it should be discussed.

I emailed Aeromotive for fuel system design help and this was their response to me...

When a “pulsation damper” is used in a fuel system it is basically a bandage, that is it’s a sign that there are either compromises in plumbing or the existing regulator that are either causing excess pulses or are unable to handle the standard pulsation found in most EFI systems. I’ve no idea what the case is in this application, but ordinarily you would not require the pulsation damper when using an Aeromotive fuel pressure regulator in conjunction with good, high flow fuel rails and corresponding port fittings, fuel lines and hose-ends. The regulators job is in fact to act as a pulsation damper, if that makes sense.

I would expect this to be a more prominent issue on an inline 6 like an RB or a JZ engine due to the length of the fuel rail. On my JZ, I will be going to a system with no damper and if it has an issue I will modify the rail to have dual feed from either end and a return from the middle to the regulator.


That is an interesting find and good job going through the process to educate yourself and find the issue. I know in the MKIV 2J that most people upgrade fuel lines, fuel rail, Injectors and FPR. I have not seen anyone mention a problem like yours afterwards. It would be interesting to see if another FPR has the same issue.

Thanks guys for the response. Appreciate it.

Before i did the modification i had no problems with a lean spot. After the modification, i had this problem. Even after replacing the fuel pump, the problem still occured.

So the pump is not the problem.

Eventhough the problem is gone, it's still interesting what caused the problem.

I contacted Fuelab about this problem, but they never heard about this. They also say that the FPR also functions as a damper.

What i think is that the injectors that i use are creating a resonance/frequentie in the fuelrail that is excactly the same as the natural frequentie of a part used in the FPR (spring/membrane). At excactly 3200 RPM. Which is causing the FPR to vibrate in a way you don't want, because of the natural frequentie of the FPR. Using a dampener flattens the frequentie and the FPR starts to work properly.

It's a litlle bit farefetched, but what else can it be.

It's indeed a good idea to try out another type of FPR to see of the problem is occuring. Maybe i will try this with a FPR from another car if i can find one.

"an Aeromotive fuel pressure regulator in conjunction with good, high flow fuel rails and corresponding port fittings, FUEL LINES and hose-ends."

My understanding of what they are saying is (make sure you upgrade everything and our fpr will help aid as a dampener as well. BUT our FPR is not a pulsation dampener.)

Looking at it from an OEM point of view, you have a average fuel pump, to hard lines that are bolted to the vehicle, to a fuel pulsation dampener, that the manufacture has done tests on what wave frequency the fuel vibrations are being transmitted so that the fuel dampener can dampen those range, when the injectors are opening and closing at lower rpm speeds. Long hard bolted down (pipes) lines that give no flex at all will generate a wave frequency when there are mechanical things pulsating (injectors) this is normal.

A pulsation dampener is used in many other systems other than cars. I don't understand why they would be informing people that pulsation dampeners are a band aid.

If you engine is asking for it, give it what it wants no?

@ Danny AE86

I think the same way about Pulsation dampers. I'm a field service engineer of high pressure plunger metering pumps. We always use a dampener because of pulsations in the piping. Causing inaccurate flow and pressure. When we test the metering pumps in the workshop we use a pressure regulator to simulate the backpressure of the customers application. The pressure regulator has no positive effect on pulsation. Because the fluid is moved by a plunger the flow and pressure is not constant, creating pulsations. To compremise these pulsations we use a Pulsation dampener. oftenly filled with nitrogen @ 70% of the working pressure to get a good working dampener. It's also impossible to maintain a constant pressure with the pressure regulator without a dampener.

For example, we have a apllication with a 100 Bar backpressure. We fill the dampener with nitrogen @ 70 Bar (70% of working pressure). When we start the pump, the flow and pressure is unstable until it reaches 70 bar. The needle of the manometer is all over the place. Above 70 Bar the pressure becomes stable and the needle is also not moving, but stable @ the desired pressure.

On a centrifugal pump we don't need a damper because a centrifugal pump has a constant flow and pressure.

So in my opnion you can see the injectors kind of as a plunger pump. Creating pulsations in the fuel rail. So to let the FPR do it's job properly you need to get rid of the pulsations. The only way to do this is to use a pulsation dampener.

What i also noticed is that the behaviour of the engine was very inconstant without the dampener over the whole rpm range. With dampener, the engine was very constant and running much smoother.

And why did the engineers from NISSAN place a dampener in the fuel line? I think they didn't use the dampener just for fun. Maybe it has a reason :)

So i don't think it's a band aid.

Ive heard of this before from injector dynamics. Its a resonance frequency issue. A good idea or to help to stop the pulsations is to use flexible rubber efi fuel hose as it naturally dampens the pulsations because it expands and contracts helping maintain constant pressure. Unlike all the hard lines etc they have no give. Also you can get a similar issue if you run a too long signal hose to your fuel pressure regulator. Keep it short as possible.

@ Danny AE86

I visited the website of Radium and they mention exactly what my problem is.

"The opening and closing of fuel injectors creates pressure pulses in the fuel rail which can lead to unstable fuel pressure. In order to achieve a safe and consistent rail pressure, a fuel pulse damper (FPD) is often necessary. The FPD's internal diaphragm will absorb oscillating pulses and stabilize fuel pressure. This correction can be measured throughout the RPM range and can often help idle surge, especially with high flow injectors. Furthermore, a fuel pulse damper can help solve erratic lean air/fuel ratio spikes, commonly experienced as "stumbling", that are difficult to tune out."

The stumbling is what i experienced @ 3200 RPM.

Yeah they make great fueling products. I'd add a fuel dampener if I were you. Like I said before. At that rpm range that you're having the issue at, its a little to high for my liking.

*thumbs up*

I went back to my tuner. The stumbling of the engine was gone, but there was still a lean spot @ 3200 rpm.

I couldn't get rid of it my self by adjusting the fueling in the ECU.

My tuner also found this a very strange issue. @ first he also couldn't adjust the fuelmap to get it in the ball park.

He finally adjusted the Wall flow compensation inside the ECU and the leanspot is almost gone. But this is only a band aid, which is masking the problem.

I'm looking on the web to find some answers about what wall flow really is. If i understand it correctly it's the way the airflow behaves entering the cilinder under various conditions depending on rpm, tps position and temperature. Which i can understand will vary a lot under different circumstances.

Maybe somebody can explain what the wall flow parameters in the ecu do. See attached picture.

Attached Files

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?