chilibluepepper

It seems this thread is headed in the right direction to answering the source of "knocking/clunking" noises affecting modified fuel systems. I think Duke hit the nail on the head regarding the fuel damper being the culprit, and the different experiences posted seem to support the following: more powerful, higher flow fuel pumps coupled with injectors operating at shorter cycles (particularly at idle), and less compliant fuel lines are amplifying the hydraulic pulsations in the system, and the stock damper cannot effectively absorb/dampen these increased "shocks."

The following excerpt summarizes the inherent pulsations that occur in fuel injected systems, and which are typically resolved via dampers in the fuel system.

"Fuel-injected internal combustion engines are well known. It is known in the art relating to engine fuel injection systems to provide pulse dampers for reducing the noise and vibration caused by pressure pulsations in fuel lines, particularly in lines feeding individual injectors and pressurized inlet lines for high pressure fuel pumps supplying fuel for direct cylinder injection. It is known that pulsations generated by the actuation of the fuel injectors can be transmitted from the engine to the body of a vehicle by a prior art rigid fuel line extending therebetween, causing the fuel line to vibrate against the body of the vehicle and thereby generate audible and undesirable noise."

Sound familiar?

In light of the preceding, the questions are... Can the stock damper be upgraded to one (at the stock location) with an increased capacity to cancel out these pulsations? Or, is the solution to add a second damper to the system, as described by Duke.

Duke can you get further info and/or pictures of your friend's setup? Is the damper he used part #930.110.602.00?

Tom M'Guinn

Thank Alex. Duke, anything you can share on this would be great.

I don't know enough about how dampers work, but would two damper offer double damping? Either way, would two dampers affect the fuel pressure? Can't help but notice the inlet port is bigger than the outlet on the stock 951 damper...

Duke

Sorry I don't have the part number. I might be able to get it in a few weeks.

A damper is basically a spring-loaded diaphragm that dampens the pressure fluctuations, so the fuel doesn't necessarily flow through it (like the Marren don't).

If I had a 951 back together I'd do a temporary install with an additional damper for back to back testing. I'm confident it will reduce most of the noise.

RolexNJ

Duke, I just went and read what you, Tom, and Alex had to say. But I am backing up here to what you said about Puppans car above. Can you explain this one? It sounds like you were saying that there is a flaw in the LR (Marren design). Ok. But David doesnt have that nor does Tom, but they have bigger pumps and the noise. How do you explain Puppan with no noise? I am lost. Bigger injectors and stock rail, and 044 pump, yet no knocking? Why would we consider two dampners when Puppan isnt having any issues. What is so special in his set up that he doesnt?

Duke

The fuel lines also plays a big part here. The braided ones are usually very stiff and doesn't absorb any of the pulsations.

IIRC Ski or Jwl replaced a short bit of the braided line with a rubber hose and which reduced the noise a lot.

Dave Lindsey also once told me that the first batch of rails had another type of braided lines with stiffer inner hose than the ones they use know which promoted the noise even more.

RolexNJ

Thanks. I talked to Ski once about this and he told me what he did, but I can't remember "specifically" where he replaced the line. Maybe he'll chime in on this or I'll send him a PM and see if he will explain what he did. I am starting to believe this may be the biggest factor here, along with softer SS lines too.

Brantley

I had never noticed a tapping sound until just recently when I added XBR braided fuel lines (from Speedforce Racing), and had my stock injectors resealed and flowed by Witchhunter.com. Everything else is stock currently. The tapping is very noticeable now at idle, and especially when the engine is cold. The tapping seems to strongest at the dampener and/or the fuel lines.

Ski

jwl, actually placed his old damper in the wheel well, made up two fittings with hose, and has zero noise. It will fit in there, by the return line but then some will ask why? It worked is all I can tell you.
Due to the exhaust note on the track car, we can't hear **** except the exhaust - however, on a street car, it can be a nagging sound.

I on the other hand, used a small rubber hose that LR sent out shortly after the group buy a few years ago. A big thing with the noise if the main fuel line is touching the body anywhere along its route. I found 4 places it was touching because the rubber insulators had worn down over the years. I used some old 3/8" fuel line. Both of these, short rubber hose and the line buffering, greatly reduced my noise; I can still hear it on a cold morning below 1200-1500 rpm. I have not tried the extra o-ring as others with the LR rail have. With the added capacity of the 044 pump, I'm sure you might be hearing more pulses, at idle and when cold.

Safe to say we know why Porsche insulated the pump and used the damper setup they used. On the other hand, with the amount of fuel going through the new rail, put a laser temp gauge on it, you might be surprised how cool it is.

Bill

I agree with Dukes assessment. There is no way a rotary fuel pump can cause a clicking noise. Rotary motors "whir" A clicking noise generally comes from the shutting of a valve. If the noise is coming from the fuel system, the only valves there, are the fuel injectors.

During operation, the fuel pump pressurizes the fuel rail. With a larger fuel pump and injectors, when the injector opens you get more fuel flow than the stock setup. With all this additional fuel flow, when the injector closes, the added fuel flow should increase the rate at which the injector closes. Kind of like a door in your house, slamming closed on a windy day. Add to this, the shock wave that is created in the fuel flow, when the injector closes. The purpose of the fuel rail damper is to minimise the shock waves or pulsations in the fuel rail. Very similar to the blow off valve for the turbo, which vents the air shock wave created when the throttle plate closes.

I have the Bosch "HV" fuel pump and 55 lb injectors, stock rail (modified to accept AN fittings and teflon fuel lines), with a stock fuel damper, and I have no ticking noise. If you have the Lindsey Rail with the aftermarket damper, perhaps that damper has a higher spring rate than the stock unit and is not effectively canceling out the pulsations.

On a side note, sound waves can travel long distances if given rigid conduits. In your case, solid fuel lines. In my industry, construction, we deal alot with sound transmition in office walls. A good sound wall (a wall that limits sound transmission) will be double framed so that the sheetrock on one side is not fastened to the same studs that the sheetrock is fastened to on the opposite side. This way sound waves can not be transmitted from one layer of sheetrock to the other, through the wall studs. Typically sound deadening insulation is weaved in between the two wall stud layers to futher stop the sound waves.

So there are two possible solutions. One. Change out the Lindsey damper with a stock unit. I would not add a stock unit in line with the Lindsey unit, because the damper with the highest spring rate would win. Two. You could isolate the fuel rail, soft/flex fuel line between the damper and rigid lines, and (put rubber insulator under the fuel rail to head mounts) EDIT: BAD IDEA, THIS WOULD RAISE THE FUEL RAIL AND ALLOW THE INJECTORS TO MOVE AND POSSIBLY LEAK. There is however, no way to deaden the sound of the larger injector pintle slamming closed, from the added fuel flow.

But then HEY..........you want more performance don't you? Ever hear a quiet race car?

And the absolute best method to quiet that white noise........turn up the stereo!

RolexNJ

Thanks Ski, I remember you guys did a few things and it worked.

Cheers,

Tom M'Guinn

Time for the next installment on this...just when you thought I'd given up. On-going testing and observations confirms that the knocking noise is without question coming from the pulsations in the hard lines under the car, not from the pump itself and not from any hammering of the injectors against the intake or fuel rail. Specifically, the knock is transmitted to the floorboard at each point where the rubber isolators attach to the studs in the floorboard. I've confirmed this several times now by removing the nuts that hold the rubber isolator in place and pulling the isolators/lines away from the floorboard. The noise goes away entirely with the isolators pulled away from the body. The rubber is fairly hard and transmits the stronger-than-stock pulsations directly to the floorboard -- which creates the knock. The colder it is outside, the harder the rubber gets, and the more knock it transmits to the floor. The rubber must be soft enough to absorb the stock-level pulsations in the line (if any), but not enough for the 044 pump and 83lb injectors at idle. So, yesterday, I made up little soft sponge-like backing pads for each of the rubber isolators, using plastic packing material, so that I could fasten the lines to the floorboard securely but without transmitting the noise. (If you hold a hockey puck against a door and knock, you still make a knocking sound, but if you hold a sponge against a door and knock, no knocking sound.) Initial tests suggest this did the trick. The floorboard knocking went away altogether yesterday and stayed quiet for about 80 miles worth of driving. I thought I had "fixed" it before, so I'll have to watch it for while to confirm, but I am very optimistic this time...

Rich Sandor

It's great that you've identified the actual cause of the noises, but you haven't gotten rid of the pulsations in the fuel lines, you've only insulated them. Now we need to confirm if a better fuel dampener will solve the problem.

Tom M'Guinn

Fully agree. Once step at a time. I've been looking for easy answers on the bigger/better damper front, but nothing has made itself obvious yet. Open to ideas of course...

special tool

Satisfactory.

Tms951

I have been following this thread for a while to see if you guys would figure it out, at this point it has gone so long I will step in and tell my story.

Over the summer my car was at Under Pressure Performance getting a standalone installed. UPP thought the sound could be a spun bearing some ware but not defantly a rod bearing. UPP did not want to go on with other work until this problem was nailed down as a standalone is point less on a potentially trashed engine. I gave the go ahead and it was nailed down to the lines, which I posted on page two. UPP builds race cars and does not use fuel rail dampeners, he removed mine and the sound basically went away. I have to give credit to Scott Gomes for figuring this out.

My set up is the Bosch pump, Lindsey rail and 72 lb. injectors. I talked to Wes at Lindsey who said the dampener was rated for up 72lb. injectors, but it seems it might be better for smaller ones. In any case I do not have the dampener on there is no thumping and no problems. Don't bother insulating and isolating things, just yank the dampener.