Fuel Line Plumbing Question
05-11-2016, 12:53 AM
#62
Rennlist Member
Thread Starter
Guys, here's a video of the engine at idle. There is quite a bit of noise but you an see the FPR gauge stays steady. The pulsing in the fuel lines isn't violent but you can feel it when you touch the fuel line.
Would a large vacuum leak cause something like this?
The car runs fine when driving. It's hard to hear the noise when driving but I believe it's still just audible.
Listen to the sound at the end of the video from inside the car. You might be able to hear the thumping sound. Could it be a vacuum line under the dash? It seems loudest under the dash near the console.
Would a large vacuum leak cause something like this?
The car runs fine when driving. It's hard to hear the noise when driving but I believe it's still just audible.
Listen to the sound at the end of the video from inside the car. You might be able to hear the thumping sound. Could it be a vacuum line under the dash? It seems loudest under the dash near the console.
05-11-2016, 01:11 AM
#63
now that is just ODD. it does sound like she is sucking air some where..... but that THUDing noise... has me stumped.... exhaust leak? does the noise change when you increase the revs?
05-11-2016, 01:50 AM
#64
Rennlist Member
Thread Starter
It's hard to tell when the rev's increase due to the overall engine noise.
It doesn't seem like the speed of the noise goes up as the rev's increase.
I'm thinking the thumping noise I hear inside the car might be the intake fuel line that goes between the two rails at the back of the engine. It was sitting pretty close to the heater valve back there and might be bouncing off it due to the pulsing of the fuel line. Like I said, the noise inside seems loudest under the dash near the center console.
I'll pull the air cleaner and check that out next but I still think I need to get the pulsing to stop too.
When you had your car set up this way could you feel a pulsing in the lines at all or were they still and quiet? Maybe I'm worried over something that's normal.
It doesn't seem like the speed of the noise goes up as the rev's increase.
I'm thinking the thumping noise I hear inside the car might be the intake fuel line that goes between the two rails at the back of the engine. It was sitting pretty close to the heater valve back there and might be bouncing off it due to the pulsing of the fuel line. Like I said, the noise inside seems loudest under the dash near the center console.
I'll pull the air cleaner and check that out next but I still think I need to get the pulsing to stop too.
When you had your car set up this way could you feel a pulsing in the lines at all or were they still and quiet? Maybe I'm worried over something that's normal.
05-11-2016, 02:54 AM
#65
That thumping noise is not normal, for sure. Could be a loose hard line sacking around. My system is still set up the same, I'm sure there are some pulses, but I am running full sequential injection now so there are no "giant" pulse waves from one whole rail firing at once. But I don't remember my L-jet set up being a pulsating beast like that
05-11-2016, 10:04 AM
#66
Developer
I think that the fuel pump is sized to be able to flow enough fuel at WOT. That may mean that at idle, its' so big that it can only run intermittently. It runs for a sec, hits max pressure, shuts off, pressure drops, turns on again. It pulses. I think that is what you are feeling/hearing. There are no electrical connections in the system that feed back to the pump to turn it on or off, so I believe its integral to the design of the pump.
Anyway, test this theory by having an associate operate the throttle for you while you place your hand on the bottom of the gas tank (where the fuel pump is). At idle, you will feel the pulsing. But at some other rpm, say 2500 for example, the fuel pump is on steady and there is no pulsing.
Its an easy test that costs zero dollars.
Anyway, test this theory by having an associate operate the throttle for you while you place your hand on the bottom of the gas tank (where the fuel pump is). At idle, you will feel the pulsing. But at some other rpm, say 2500 for example, the fuel pump is on steady and there is no pulsing.
Its an easy test that costs zero dollars.
05-11-2016, 12:26 PM
#67
Former Vendor
I think that the fuel pump is sized to be able to flow enough fuel at WOT. That may mean that at idle, its' so big that it can only run intermittently. It runs for a sec, hits max pressure, shuts off, pressure drops, turns on again. It pulses. I think that is what you are feeling/hearing. There are no electrical connections in the system that feed back to the pump to turn it on or off, so I believe its integral to the design of the pump.
Anyway, test this theory by having an associate operate the throttle for you while you place your hand on the bottom of the gas tank (where the fuel pump is). At idle, you will feel the pulsing. But at some other rpm, say 2500 for example, the fuel pump is on steady and there is no pulsing.
Its an easy test that costs zero dollars.
Anyway, test this theory by having an associate operate the throttle for you while you place your hand on the bottom of the gas tank (where the fuel pump is). At idle, you will feel the pulsing. But at some other rpm, say 2500 for example, the fuel pump is on steady and there is no pulsing.
Its an easy test that costs zero dollars.
The stock pumps certainly have no circuitry to turn themselves on and off by sensing pressure.
I guess this could be incorporated into an aftermarket pump....
05-11-2016, 12:27 PM
#68
Former Vendor
That thumping noise is not normal, for sure. Could be a loose hard line sacking around. My system is still set up the same, I'm sure there are some pulses, but I am running full sequential injection now so there are no "giant" pulse waves from one whole rail firing at once. But I don't remember my L-jet set up being a pulsating beast like that
05-11-2016, 12:33 PM
#69
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Reminder that the system is hydraulic, so no dampening is available from the fluid itself. The pump has a flow-vs-head curve, flow drops off as discharge pressure increases. The fuel pressure regulator is "analog", responding only after it sees changes in upstream pressure. With stock engine management, all the injectors fire together in a "batch". Last but not least, fuel has mass and therefore inertia as it flows in the piping. The pump has a non-linear response lag, the inertia of the fuel in the piping introduces another (exponential) response lag, and the fuel pressure regulator has a fixed response lag. The frequency and duration of the pulses through the injectors provide the excitation needed to get the system to "hammer", as the flow of fuel is started and slowed. At some frequencies and durations, and particularly when they are low, the hammering will be most apparent. Porsche and Bosch thought they were serious enough to deserve the pressure dampers to smooth them out some. Their reasons probably included not being able to maintain consistent and even fuel pressures above the injectors, with flows mismatched among the cylinders.
Solutions include dampers, as we know. The causal excitation component can be somewhat reduced by changing to sequential injection, but that's not something easily done without a new engine management package. Increasing the sizes of the fuel lines and rails will help with the unbalanced flows among cylinders, but adds to the mass (and inertia) that the fuel pressure regulator must deal with if mechanical dampers are not included in the design.
From a process point of view.
Solutions include dampers, as we know. The causal excitation component can be somewhat reduced by changing to sequential injection, but that's not something easily done without a new engine management package. Increasing the sizes of the fuel lines and rails will help with the unbalanced flows among cylinders, but adds to the mass (and inertia) that the fuel pressure regulator must deal with if mechanical dampers are not included in the design.
From a process point of view.
05-11-2016, 12:35 PM
#70
Former Vendor
It's hard to tell when the rev's increase due to the overall engine noise.
It doesn't seem like the speed of the noise goes up as the rev's increase.
I'm thinking the thumping noise I hear inside the car might be the intake fuel line that goes between the two rails at the back of the engine. It was sitting pretty close to the heater valve back there and might be bouncing off it due to the pulsing of the fuel line. Like I said, the noise inside seems loudest under the dash near the center console.
I'll pull the air cleaner and check that out next but I still think I need to get the pulsing to stop too.
When you had your car set up this way could you feel a pulsing in the lines at all or were they still and quiet? Maybe I'm worried over something that's normal.
It doesn't seem like the speed of the noise goes up as the rev's increase.
I'm thinking the thumping noise I hear inside the car might be the intake fuel line that goes between the two rails at the back of the engine. It was sitting pretty close to the heater valve back there and might be bouncing off it due to the pulsing of the fuel line. Like I said, the noise inside seems loudest under the dash near the center console.
I'll pull the air cleaner and check that out next but I still think I need to get the pulsing to stop too.
When you had your car set up this way could you feel a pulsing in the lines at all or were they still and quiet? Maybe I'm worried over something that's normal.
At idle, there is a very tiny amount of fuel being used. If the pump overwhelms the regulator's ability to return fuel, nasty things happen. This is common when people use an 044 pump and don't pay attention to the regulator's ability to return fuel.
Although I'd guess that an Aeromotive regulator should be able to return a large volume of fuel, this might be worth looking at....
05-11-2016, 12:53 PM
#71
Rennlist Member
Thread Starter
Just to be clear, it is a stock pump. I'm running -06 fuel lines. I will try Carl's suggestion about feeling if the pulses can be felt at the gas tank pump area. Is there any reason I shouldn't be able to use the original damper on the set up I gage now?
Last edited by pokegama; 05-11-2016 at 02:23 PM. Reason: Stock pump
05-11-2016, 03:24 PM
#73
Developer
Greg is correct - there is no circuitry or device within the pump that shuts it on and off when it reaches certain pressures. I worded my previous post poorly.
I'd still like you to run that test - place your hand on the bottom of the gas tank on the fuel pump cover... does it pulse only at idle and not when the engine is operating at higher rpms?. That would be useful to know.
ALSO: how much gas do you have in the tank? Is it low on fuel? I can contemplate a situation where the pump is sucking air and that could make it "pulse"...
The answer to that is simple: add some gas to the tank and see if the "pulsing" is reduced or eliminated.
I'd still like you to run that test - place your hand on the bottom of the gas tank on the fuel pump cover... does it pulse only at idle and not when the engine is operating at higher rpms?. That would be useful to know.
ALSO: how much gas do you have in the tank? Is it low on fuel? I can contemplate a situation where the pump is sucking air and that could make it "pulse"...
The answer to that is simple: add some gas to the tank and see if the "pulsing" is reduced or eliminated.
05-11-2016, 03:24 PM
#74
Former Vendor
I'm still not following the logic of removing them.....so I'm not going to be much help......since it is not something I've ever done.
You boys have fun, with this.
05-11-2016, 03:33 PM
#75
Developer
Is there any reason I shouldn't be able to use the original damper on the set up I have now?
However, it may mask a problem. Others (like Ducman in this thread) have our rails, no dampers, and -6 AN fuel lines and do not have this problem. Your system now is larger and is fluid dampened. So there is something amiss, adding a dampener now may just hide it.
BTW, how did you connect the rear of the fuel rails to the after-market FPR? Any tight bends, or smaller-than-6 fittings in that system? I'm looking for a restriction to the return to the gas tank. If you post a pic or two of the back of the engine so we can see how you have plumbed it, we might see something.