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Discussion Starter · #1 · (Edited)
Anyone have any experience with fuel pulse dampers?

I recently switch from sd80lb injectors to Bosch 210s and was encountering a lean spot in the fuel map around 2k rpms that no amount of tuning would remedy. I had a theory that the larger injectors were creating a harmonic that did not play nice in that area and installed a radium engineering inline damper on the driver rail. So the fuel system currently looks like this. -10 feed to the regulator in the passenger fender, -10 to a y block splitting to -8 feeding the back of each rail with the damper screwed into the back of the driver rail and a -6 crossover in the front
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After install the lean spot was gone and the car drove and idled much smoother so I thought the problem was cured. However after reviewing the logs the passenger side is still experiencing the same lean spot, although significantly improved, and the AFR fluctuates quite a bit more than the driver side that has the damper. My theory is the distance from the damper to the passenger rail is not allowing it to sufficiently dampen the pulses in that bank.

In order to remedy this I could install a second damper on the driver rail like below. I am sure this is the most effective but I am not sure it is needed and it is the most costly option.
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Another option is to run -10 from the regulator to a tee on the passenger rail and try to install the regulator between the two rails and hope the one is sufficient to dampen both rails. I also had a member of another forum claim running a tee off the rail contributed to his engine failure due to improper fuel supply. From what I remember from my fluids classes this seems highly unlikely however the thought is still in the back of my head as a concern.
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If anyone has experience running aftermarket dampers what are your opinions on the single fpd between the rails vs one mounted directly to each rail?
I am sure someone will also mention that the deadhead layout is not optimal and that the regulator should be mounted after the rails. I am aware of that and I am trying to avoid that purely for aesthetics. There's also no guarantee that the large injectors and pump wouldn't still have the same harmonic and cause the same issue putting me in the same situation.

Edit: Front crossover is -6 not -4 as shown in diagrams.
 

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1965 Superformance 427 Cobra, & 2022 BMW M850
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Tommy, dampers can provide much of the good experience you are having. They have a down side for supercharged, performance vehicles. Inside each damper is a diaphragm that absorbs the pulsations in the fuel rail. For non supercharged daily drivers these devices are fairly reliable but they only operate around 3 BAR (43.5 psi). In boosted applications with a boost referenced pressure regulator the fuel system pressures become ambient plus boost. If you have 20 psi of boost the device will see the base fuel pressure (43.5 psi) plus the boost (20 psi) for more than 60 psi of fuel pressure at the fuel rail, even more at the pump.

If a damper diaphragm ages and cracks it can leak fuel onto the hot engine. We all know the end game for gasoline running over a hot engine. If I were you I would attempt to find an alternative solution to the problem.


Ed
 

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Discussion Starter · #3 ·
Ed I agree they are a bit of a band aid to an issue that is introduced into the fuel system one way or another. I believe in my case the big pwm driven fuel pump along with the large injectors are the main contributors. Unfortunately I feel like any changes made to the system routing would be little more than guesses on whether or not they would remedy the issues. I also believe most any modern efi fuel system incorporates a fpd somewhere in the system which leads me to believe there is some justification for them.

On the note of increased differential pressures the aftermarket radium engineering dampers incorporate a boost reference port to maintain a constant delta. Incase you are unfamiliar with them; Fuel Pulse Damper, Inline Kits. They are a very nice piece that give a variety of mounting options. I am running the inline version screwed directly into the rear of the fuel rail with a 90° hose end coming off of it. This gives just enough room to clear the firewall and makes for a pretty nice mounting solution.
 

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A couple of thoughts, Tommy ...

PWM capable pumps are typically used in return-less systems. That doesn't mean they can't be used in a return style system, they can. When you do, you simply run them at system voltage or higher (if you use a BAP style device). The PWM capability while available, simply is not necessary and even if it was, it does not produce the pressure waves you are seeing.

Those types of pressure waves are typically the result of a large injector feeding off a moderate to low volume (for the indicated HP) fuel system. The spike occurs as each injector closes and before the next injector opens. The phenomena is the physical manifestation of a lower than optimum fuel delivery system catching up pressure-wise with rails that showing a lower but rising pressure between injection events. When the pump finally catches up there is a hydraulic 'bang' that is absorbed by the damper.

If your fuel system is robust (capable of fueling in excess of your engine's maximum power level). rail pressures never drop because the fuel reserve is so great, i.e. the rail pressure never falls below the system baseline. I am not talking about idle where the fuel pressure falls to maintain the delta pressure across the injector that the ECU expects to see at idle and manifold vacuum. I am talking about above idle, engine rpm.

When you see the pressure and corresponding lambda (or AFR) variations you are speaking about, that is caused by an engine appetite for fuel that exceeds fuel system's delivery capability. Now that may be because of line sizing or it could be because of inadequate fuel pump sizing or both. There is a third possibility that is blessedly simple to fix. If the pump was sized correctly, the lines are sized correctly and the phenomena is presenting itself, the fuel pump is likely in the final stages of its useable life and a simple replacement will fix the problem.

The reason you see the lambda (or AFR) variations is that the ECU is expecting to see a delta pressure (let's use Ford numbers) of 39.15 psi but the pump delivery capability has been diminished to the point it can only deliver 32 or 35 psi. The ECU does an injector pulse width calculation for a 39.15 psi delta pressure and comes up with some micro second injector open metric for the required fueling.

Because the fuel rail pressure is a little low, the fuel charge is also a little short of the mark and you detect the leaner than commanded effect for that cylinder. While all this is going on, the fuel pump in the background is paddling as hard as it can to pump enough fuel to maintain the commanded delta pressure at the injector — but it can't quite make it.

When the injector slams shut the pump is at a full boogie but is still short of the mark. As it catches up there is a hydraulic bang in the fuel system when it hits the target fuel pressure. That bang is what the pressure damper softens but as you discovered the AFR was still short of the target fueling mark you were commanding in the tune.

If you are running a -10AN line to the regulator and a -8AN to each rail (as you are), your plumbing is OK. Use the fuel system calculator in the TToC to decide how much fuel pump you want to have available. I like to see an injector duty cycle around 50 to 70 %, with the 50% side of the scale being the more desireable. Likewise you want to see a fuel pump volume that is 50% to 75% more than is necessary to both provide for good head room but also to mitigate the hydraulic shock waves in the fuel rail between injection events..

If you run pump gas remember that it is really E-10 with a stoich point of 14.08 not 14.7 like pure gas. Your cruising around and accelerating in traffic lambda should be about 0.80 to 0.82. Don't go leaner than 0.82. A lambda of 0.82 is equivalent to an AFR (with E-10) of 11.55 (14.08*0.82). You are walking a very fine line here.

A better place to be is 0.80 lambda or 11.26 AFR (14.08*0.80). When the car is under power accelerating hard you will want to be in the 0.75 lambda range to provide the equivalent of an accelerator pump shot like the old carburetors. If your ECU provides for transient fueling (most do) that is where you will set the accelerator pump shot size, and timing.

BTW not withstanding all this fancy science stuff, be sure the Stoichiometric point is properly set in your ECU for the fuel you are running. If not all the science stuff isn't going to amount to a row of beans.

The thing about ruptured diaphragms and fuel pouring over a hot engine at 40 or so psi if not higher, is a clear and present danger. Whenever possible I like to side step the danger stuff — you will live a happier life.


Ed
 

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I don't like the -4 crossover. IMO, I feel this line should hold the save volume as the rails which can minimize some of the pulsing when fuel is required to feed an injector/rail.

Your first diagram is how the fuel lines and tee should be laid out so don't let anyone tell you different. Return the fuel that is not needed for the engine before it hits the rails..perfect!

Intake manifold and TB layout can affect how cylinders are fed so it may not be the fuel system that is the issue but instead air distribution. I have two cylinders that run leaner than the rest so additional tuning was done to compensate for those cylinders. How about a pic of the induction for those of us that don't know your setup?

ks
 

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I'm probably the guy that mentioned having the T at the back of the passenger rail. That wasn't the reason for my engine failure, but it didn't help things. The number 1 piston had detonation marks on it while the driver side pistons looked fine. My assumption was the passenger side rail wasn't getting the same pressure as the driver side since the driver side still had tbe FRPS to monitor the pressure. I was running 80lb injectors with stock rails at the time. And I was still returnless. I had weird bank to bank STFT's well. I really wish I had a standalone when I had that old set up.

Anyway, FWIW, I have a lean spot just off idle I'm trying to tune out. It's really hard to catch in a log as the engine passes that point really quick. Its right around 1100rpm and at a very light throttle. Like just past creeping through traffic light. I did manage to catch that on a log and run it through VE Analyzer. I noticed it added quite a bit of fuel to that spot in the trim table. I haven't had to a chance to drive it since making that change though. I'll add that I'm return style with ID1050X injectors.

This is really a long winded way of saying you might just need to adjust your VE/Trim table a little more to get rid of that spot.
 

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Does a lean spot at 2000rpm even matter?
 

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This is both a drivability and ultimately a parts issue guys. Tuning for max power is pretty straight forward, tuning for drivability is noticeably more difficult. Greg Banish has an excellent DVD on the subject. The DVD is Calibrated Success Advanced Tuning Series Ep. 1-4. The DVD is around $400 through Summit. If you go to Greg's site, Calibrated Success it is $199. The price tag sounds high, the knowledge inside is priceless. I highly recommend this DVD. This link will take you directly to it, click here => Adv Tuning Series. It will give you chapter and verse on tuning for drivability among many other things. The only other place I have heard or seen this approach before is Andre Simon's HP Academy in Australia. Andre will teach you the same techiniques for about the same price but you don't get a DVD although you can log on to the HP Academy tutorial for review whenever you wish.

As a closing thought, a lot of guys retain a gasoline stoich point in the tune irrespective of whether or not they run on gas, E-10, E-85 or methanol. This is a mistake. Your ECU, in particular an aftermarket unit, will make provisions for correcting the stoich point based on the fuel you are running. If you use gasoline the stoich point is 14.7, E-10 is 14.08, E-85 is 9.77, E-100 is 9.01 and methanol is 6.42.

These things turn out to make tuning much easier if you use them. Additionally if you tune in lambda the whole process gets substantially more straight forward. Banish will speak to that in his DVD. Here is a screen shot from an updated Fuel System Calculator I'll be adding to the TTOC over the next few weeks. It graphically shows you the lean line in the sand that you don't want to go over and it does it in both lambda and AFR numbers.
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Ed
 

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Every time I drive my 1600whp street car, I am amazed how perfect it drives. I could literally drive the car every day if I wanted to. I don't have to touch the pedal to start it, it idles perfect, cruises perfect, it idles down perfect when I slow down, everything about it is simply fantastic. I have a traditional designed fuel system with the y-block feeding the back of the rails, three whisper quiet walbro 450 fuel pumps and the best injectors money can buy (deka 220's). Every part of the system being done right makes a huge difference.

@96slowbra, I would do a more traditional style fuel system and ditch the deadhead and fuel damper. It will likely fix all of your problems. I used to run the Bosch 210's also, never had an issue like you describe. Good luck.
 

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I've thought about switching to lambda, but I've been lazy on it honestly. The ECU does enough "thinking" for me that it really hasn't been much of a concern. I went the hard way on my flex fuel as I had two VE tables to tune. But that allowed me to run the E85 a little richer on the gas scale as it seems to like it.

FWIW, the guys at Megasquirt recommended to Josh to leave the tune set up for gas and use the flex fuel part to run E85. He's on E85 full time so he could change the stoic and all that if he wanted.

Maybe the style of return matters as you get into bigger set ups. I have twin 450's (I wouldn't call them whisper quiet though) and ID1050X injectors. The car drives just fine. The cold start needs a little tweaking, but that hasn't stopped me from driving it to work occasionally. And usually dealing with traffic in the process. I'm running a deadhead fuel system mostly to keep the engine bay clean.
 

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Discussion Starter · #11 ·
I am not used to this level of traffic on the forums anymore. Thanks for the feedback guys especially Ed, your thought out informative responses never cease to amaze me.

I have a full build thread on the car going but a quick background on the setup is a 96 cobra with c heads, Mach 1 lower, 96 upper via adapter, Novi 2000 running a wastegate for boost control, fuelab 42401 pump, bosch 210lb injectors, e85 and d585 coils all controlled by a MS3pro Ultimate. I was also mistaken in my original post the crossover is a -6 not -4. I know it's not an 03/04 cobra but the level of technical knowledge in this section in particular is unrivaled by any other location I have found.
Car Vehicle Hood Blue Motor vehicle


I am currently only seeing ~13lbs boost so the fuel system is significantly oversized, thus the reason for running the pump pwm. The flow simply isn't needed plus the MS3 has the capability to run pwm so why not. I am very confident that none of the fuel system is causing the issue due to being undersized or due to failing equipment. The car was running perfectly fine with sd80 injectors but was running about 95% duty cycle at 6500rpm. The only change was the bosch 210 injectors that resulted in the lean spot around 2k rpms which was affecting drivability. Startup and idling was essentially unaffected and required only minor tweaks after adjusting for the new injectors. It also pulls clean to ~6700rpm with no issues right now. I haven't had time to work up any higher than that just yet.

The tune was originally done using 93 pump factoring in the e10 content of pump gas. I've been utilizing a flex fuel sensor and letting the MS3 interpolate for the e85 content for close to two years now with no apparent issues relating to that method. The fuel pressure shows no dips when the 2k rpm lean spot occurs or any where else in the rpm range. I tried tuning out the lean spot manual, with VEAL as well as megalogviewer. Both VEAL and Megalogviewer resulted in a mountain of fuel in the troublesome area in excess of 100% higher than the surrounding cells. Manually I tried a more subtle approach but could never get it to lean out less than ~16:1 in that spot. When rolling through that area of the map it would shoot from 13:1 to 18-19:1 on the gauge inside the car. I do tune in lambda but I haven't taken the time to change the gauge in the car over yet.

I did have an interesting phone call with a member of another forum today. He said his shop has built several cobras using the fragola style ptfe stainless hose and all of them that had the black coating on them had issues with fuel pulsation causing lean spots. This occurred with both dead head return as well as traditional return fuel systems. The only solution he had found to eliminate the issues was running fuel pressure dampers or swapping over to an extremely expensive hose, ~$90/ft, that required crimped ends. I don't remember the specific hose now unfortunately. The theory behind the black coated hoses in particular causing issues is the coating prevents the stainless brain from flexing which prevents the hose from absorbing any potential hammer in the fuel system.
 

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Discussion Starter · #12 ·
Looks like I have bigger issues to deal with for now. Went out to get some groceries and cam home on a trailer. Car lost all spark for some reason at the end of a pull and stranded me on the side of the road. Log looked ok no idea why it shut off. Pulled the plugs when I got home just to ease my mind and they all looked ok. Hoping to have some time this weekend to further diag.
 

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Assuming nothing is fried, you might get off fairly easily, Tommy. With all eight dead it sounds like a grounding or power line attachment issue.

Ed
 

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Discussion Starter · #14 ·
Assuming nothing is fried, you might get off fairly easily, Tommy. With all eight dead it sounds like a grounding or power line attachment issue.

Ed
I agree Ed. After seeing the the plugs were ok and no fuses were blown I was slightly less concerned. It's never a good feeling loading up you car on the side of the road though. I was able to look at it for a few minutes on lunch and it looks like I have an open ground to the block from the coil connector. Odd it would happen out of no where after a pull but at least I have a culprit to look into.
 
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