running lean of stoich - lean is not the enemy, stoich is!
02-09-2007, 03:55 AM
#61
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Thread Starter
larry,
check again, also check your reading comprehension.
never said manifold pressure is binary. i said the vacuum source on the intake side of the throttle plate, is binary, for all practical purposes. put a vacuum gauage on that throttle based vacuum source. as soon as you have some reasonalbe level of throttle, the vacuum is not effective and not doing anything to the fuel pressure in the rails. this is why i can run the vacumm or not run the vacuum and guess what, fuel air ratios are not changed.
go to the dyno and do an experiement. with our without vacuum. I have , you probably havent.
mk
check again, also check your reading comprehension.
never said manifold pressure is binary. i said the vacuum source on the intake side of the throttle plate, is binary, for all practical purposes. put a vacuum gauage on that throttle based vacuum source. as soon as you have some reasonalbe level of throttle, the vacuum is not effective and not doing anything to the fuel pressure in the rails. this is why i can run the vacumm or not run the vacuum and guess what, fuel air ratios are not changed.
go to the dyno and do an experiement. with our without vacuum. I have , you probably havent.
mk
Originally Posted by Larry928GTS
Measured it.
Binary responses?
Slightly longer, non-binary response for those that want it below:
Mark, every one of those statements that you made and I responded to are absolutely wrong. They're so wrong, and there are so many of them, that I have to think the statements were made as some kind of a troll attempt.
Fuel injector size is rated at a fairly standardized fuel pressure of 3 bar, which is 43.5psi. The injector flows the rated amount of fuel with that pressure differential across it. Changing the pressure differential across the injector will change the amount of fuel flow through it. Increasing the pressure differential across the injector will increase the amount of fuel flowing through it, and decreasing the pressure differential across it will reduce the amount of fuel flowing through it. The stock '87 and later 928 injectors are rated at 19lb/hr, but they don't flow 19lb/hr in a 928 engine. Why? Because the stock fuel pressure is higher than the 43.5psi that the injectors get rated at, so in a 928 engine they flow more than 19lb/hr.
Manifold vacuum is NOT an either all or nothing situation, as Mark stated. If it were, you'd have no part throttle, only idle and full throttle. Think about it. If the manifold pressure was the same just off idle as it is at full throttle, why would the car go faster at full throttle than it does just off idle? The pressure differential across the intake valves would be the same in either case, so airflow into the cylinders would be the same as well. I've seen quite a few vacuum gauges. They all had numbers on them, and not just "Yes" and "No" written on their faces for the needle to point to.
?
Binary responses?
Slightly longer, non-binary response for those that want it below:
Mark, every one of those statements that you made and I responded to are absolutely wrong. They're so wrong, and there are so many of them, that I have to think the statements were made as some kind of a troll attempt.
Fuel injector size is rated at a fairly standardized fuel pressure of 3 bar, which is 43.5psi. The injector flows the rated amount of fuel with that pressure differential across it. Changing the pressure differential across the injector will change the amount of fuel flow through it. Increasing the pressure differential across the injector will increase the amount of fuel flowing through it, and decreasing the pressure differential across it will reduce the amount of fuel flowing through it. The stock '87 and later 928 injectors are rated at 19lb/hr, but they don't flow 19lb/hr in a 928 engine. Why? Because the stock fuel pressure is higher than the 43.5psi that the injectors get rated at, so in a 928 engine they flow more than 19lb/hr.
Manifold vacuum is NOT an either all or nothing situation, as Mark stated. If it were, you'd have no part throttle, only idle and full throttle. Think about it. If the manifold pressure was the same just off idle as it is at full throttle, why would the car go faster at full throttle than it does just off idle? The pressure differential across the intake valves would be the same in either case, so airflow into the cylinders would be the same as well. I've seen quite a few vacuum gauges. They all had numbers on them, and not just "Yes" and "No" written on their faces for the needle to point to.
?
Last edited by mark kibort; 02-09-2007 at 04:15 AM.
02-09-2007, 04:15 AM
#62
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Thread Starter
larry,
Besides measureing vacuum from these lines, you have to understand how the fuel regulator works. it keeps constant pressure via the spring diaphram system, that, depending on the volume of fuel used, this self regulating mechamism allows more fuel to return to the gas tank. the more you are flowing through the injectors, the the more spring diaphram can keep the pressure up by closing off the return line. in no way is the vacuum line part of this process, except for control of fuel pressure during idle. a quick test is to look at a fuel pressure gauge. As i mentioned, my 84s with the 5 liter euro engine ran 47psi under idle and 52psi at part and full throttle.
the injector duration timing determines fuel flow as you say. you got that part right.
as far as probst. Isnt he one of the authors that said " Ljetronic is unresponsive to modifications to headers, cams, throttle body mods, etc." Yet i was able to gain 100hp with no mods to the Ljet system, but a bump to fuel pressure .
Again, if the vacuum line was so important, wouldnt i have seen some issues by having mind disconnected over the past year? last season, i probably had it connected 1/2 the time. the reason i have it disconnected, idle is higher and i think its better to have more fuel on decel , along with removing my off-idle microswitch as well, to keep idle higher and better rpm recovery during throttle blips.
Besides measureing vacuum from these lines, you have to understand how the fuel regulator works. it keeps constant pressure via the spring diaphram system, that, depending on the volume of fuel used, this self regulating mechamism allows more fuel to return to the gas tank. the more you are flowing through the injectors, the the more spring diaphram can keep the pressure up by closing off the return line. in no way is the vacuum line part of this process, except for control of fuel pressure during idle. a quick test is to look at a fuel pressure gauge. As i mentioned, my 84s with the 5 liter euro engine ran 47psi under idle and 52psi at part and full throttle.
the injector duration timing determines fuel flow as you say. you got that part right.
as far as probst. Isnt he one of the authors that said " Ljetronic is unresponsive to modifications to headers, cams, throttle body mods, etc." Yet i was able to gain 100hp with no mods to the Ljet system, but a bump to fuel pressure .
Again, if the vacuum line was so important, wouldnt i have seen some issues by having mind disconnected over the past year? last season, i probably had it connected 1/2 the time. the reason i have it disconnected, idle is higher and i think its better to have more fuel on decel , along with removing my off-idle microswitch as well, to keep idle higher and better rpm recovery during throttle blips.
Originally Posted by Larry928GTS
Measured it.
Binary responses?
Slightly longer, non-binary response for those that want it below:
Mark, every one of those statements that you made and I responded to are absolutely wrong. They're so wrong, and there are so many of them, that I .
?
Binary responses?
Slightly longer, non-binary response for those that want it below:
Mark, every one of those statements that you made and I responded to are absolutely wrong. They're so wrong, and there are so many of them, that I .
?
02-09-2007, 04:30 AM
#63
My post was primarily intended to inform others how the system works when it's operating correctly. I've seen more than enough threads that go this route to know that it's pointless to try to correct Mark and misinformation in his posts.
02-09-2007, 04:38 AM
#64
Rennlist Member
Thread Starter
larry, its reality. go put a finger on the vacuum line on the fuel regulator. it goes away at part throttle and beyond. your description is not correct. the vacuum is not an integral part of how the device works. dont you get that the fuel flow dictates how much fuel is routed back to the fuel tank? this is why you can screw the fuel regulator spring tension and allow more or less fuel to return back to the tank. anyway, it sure seems like you havent played much with them. as you know, not only do i get 20mpg driving to the track, i have dynos that show part throttle and fuel throttle mixtures, and have used fuel pressure gauges to monitor fuel pressure at different throttle settings, with and without the vacuum connected. without it connected, there is no change, but at idle where it is used to pull back the pressure so that the closed loop system is not fighting the fuel pressure as much (rich lean hunting via the o2 sensor)
MK
MK
Originally Posted by Larry928GTS
My post was primarily intended to inform others how the system works when it's operating correctly. I've seen more than enough threads that go this route to know that it's pointless to try to correct Mark and misinformation in his posts.
02-09-2007, 10:52 AM
#65
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Originally Posted by mark kibort
larry,
Besides measureing vacuum from these lines, you have to understand how the fuel regulator works. it keeps constant pressure via the spring diaphram system, that, depending on the volume of fuel used, this self regulating mechamism allows more fuel to return to the gas tank. the more you are flowing through the injectors, the the more spring diaphram can keep the pressure up by closing off the return line. in no way is the vacuum line part of this process, except for control of fuel pressure during idle.
Besides measureing vacuum from these lines, you have to understand how the fuel regulator works. it keeps constant pressure via the spring diaphram system, that, depending on the volume of fuel used, this self regulating mechamism allows more fuel to return to the gas tank. the more you are flowing through the injectors, the the more spring diaphram can keep the pressure up by closing off the return line. in no way is the vacuum line part of this process, except for control of fuel pressure during idle.
The fact is that manifold vacuum is a function of throttle opening. Any novice piston engine pilot knows this and is responsible for engine management based on this as one of the 3 critical data points of "vacuum", RPM and EGT. Vacuum varies relatively smoothly, albeit non-linearly across the full range of throttle opening.
If you can grasp that and apply that fact to the operation of the fuel pressure regulator, it will become obvious that this variable force is applied to the vacuum diaphram in the FPR in the same continuously variable way that it is created, that being in direct relationship to the throttle opening. That varying force is applied directly to the spring (via the diaphragm) that controls the part of the FPR that you do understand. This throttle dependent force directly affects the force applied by the spring to the fuel restriction orifice, thereby controlling absolute fuel rail pressure proportionally to full range of throttle position.
If you continue to disbelieve this basic truth about vacuum in an air-throttled engine, I recommend that you connect a vacuum guage to the intake manifold (NOT throttle body) of the vehicle of your choice and go out on the road. Note the vacuum readings at idle, and then at steady state speed, in 10 mph intervals, up tp 100 mph. I guarantee you that these vacuum numbers will be different from each other, progressing from somewhere around 18" at idle, downward toward 0" where the throttle is wide open.
Please either learn this or drop it. You have much valuable experience to share here, but this agruement is past entertaining!
02-09-2007, 12:06 PM
#66
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Thread Starter
Once again, you are falling into the misundertanding trap. i never ever said manifold pressure didnt change with different power setttings. they are intimately related. who, more than me, has talked about varied vauum levels in the intake relating to power levels of the 928 or any engine? remember discussion regarding pressure drop across the intake, air box vacuum levels , ram pressure, volumetric efficiency, etc etc.???
the point you are clearly missing and this is frustrating for you, is that the vacuum driving the "idle fuel pressure pull back pressure" is drawn from the small port on the backside of the throttle plate venturi. if they (engine designers and fuel reg designers) wanted the fuel regulator to be controled by vacumm pressure , like a MAP system works ( by the way, what you described is what a MAP system does, but it doesnt work on the fuel regs it works on the ECU to control injector duration), they would have connected the fuel regs to a port ON the intake manifold. in fact, the small amount of vacuum through the tiny port, doesnt do much pull back of the spring, unless you are at idle. past that , it doesnt do much. the fuel rail pressure control is via the diaphram . If the fuel demands are light, then the pressure on the diaphram, is greater and the return line gets the most amout of fuel running back to the tank. in an extreme case, think about WOT creating 500hp. you may be getting near the max flow capabilities of the fuel pump. at this point, there would be no fuel woud be returing to the tank. but, consider WOT at 2000rpm , same engine. still there is no vacuum in the intake nor at the fuel reg vacuum port, but the fuel pump has pressure and flow to exceed demands. what happpens, the pressure of the fuel not needed , pushes on the back side of the diaprham, opening the return line to the fuel tank, thus this becomes a self regulating pressure system for the fuel rail. if you don tbelieve this, all you have to do is look at a fuel pressure gauge as said, and blip the throttle , go on a dyno an also removed the vacuum lines to see if anything changes. it doesnt.
If i didnt understand this,and what i said wasnt true, my dyno runs wouldnt have the same fuel air ratios, and my fuel pressure would change at varied throttle positions. it doesnt. when it does change is off idle with the vacuum connnected. with it not connected, idle and WOT pressure is the same.
Mk
pressure on the diaphram and all the fuel would be going to the injector rail. at this point, the return line be closed.
Manifold pressure is extricably tied to power and mass flow throught the engine. there is no debate there, and if you read my last post regarding this, you would have understood this point.
Mk
the point you are clearly missing and this is frustrating for you, is that the vacuum driving the "idle fuel pressure pull back pressure" is drawn from the small port on the backside of the throttle plate venturi. if they (engine designers and fuel reg designers) wanted the fuel regulator to be controled by vacumm pressure , like a MAP system works ( by the way, what you described is what a MAP system does, but it doesnt work on the fuel regs it works on the ECU to control injector duration), they would have connected the fuel regs to a port ON the intake manifold. in fact, the small amount of vacuum through the tiny port, doesnt do much pull back of the spring, unless you are at idle. past that , it doesnt do much. the fuel rail pressure control is via the diaphram . If the fuel demands are light, then the pressure on the diaphram, is greater and the return line gets the most amout of fuel running back to the tank. in an extreme case, think about WOT creating 500hp. you may be getting near the max flow capabilities of the fuel pump. at this point, there would be no fuel woud be returing to the tank. but, consider WOT at 2000rpm , same engine. still there is no vacuum in the intake nor at the fuel reg vacuum port, but the fuel pump has pressure and flow to exceed demands. what happpens, the pressure of the fuel not needed , pushes on the back side of the diaprham, opening the return line to the fuel tank, thus this becomes a self regulating pressure system for the fuel rail. if you don tbelieve this, all you have to do is look at a fuel pressure gauge as said, and blip the throttle , go on a dyno an also removed the vacuum lines to see if anything changes. it doesnt.
If i didnt understand this,and what i said wasnt true, my dyno runs wouldnt have the same fuel air ratios, and my fuel pressure would change at varied throttle positions. it doesnt. when it does change is off idle with the vacuum connnected. with it not connected, idle and WOT pressure is the same.
Mk
pressure on the diaphram and all the fuel would be going to the injector rail. at this point, the return line be closed.
Manifold pressure is extricably tied to power and mass flow throught the engine. there is no debate there, and if you read my last post regarding this, you would have understood this point.
Mk
Originally Posted by BrianG
This is getting ridiculous Mark. The thing that is the most frustrtating is that while you are wrong, you are not uncertain.
The fact is that manifold vacuum is a function of throttle opening. Any novice piston engine pilot knows this and is responsible for engine management based on this as one of the 3 critical data points of "vacuum", RPM and EGT. Vacuum varies relatively smoothly, albeit non-linearly across the full range of throttle opening.
If you can grasp that and apply that fact to the operation of the fuel pressure regulator, it will become obvious that this variable force is applied to the vacuum diaphram in the FPR in the same continuously variable way that it is created, that being in direct relationship to the throttle opening. That varying force is applied directly to the spring (via the diaphragm) that controls the part of the FPR that you do understand. This throttle dependent force directly affects the force applied by the spring to the fuel restriction orifice, thereby controlling absolute fuel rail pressure proportionally to full range of throttle position.
If you continue to disbelieve this basic truth about vacuum in an air-throttled engine, I recommend that you connect a vacuum guage to the intake manifold (NOT throttle body) of the vehicle of your choice and go out on the road. Note the vacuum readings at idle, and then at steady state speed, in 10 mph intervals, up tp 100 mph. I guarantee you that these vacuum numbers will be different from each other, progressing from somewhere around 18" at idle, downward toward 0" where the throttle is wide open.
Please either learn this or drop it. You have much valuable experience to share here, but this agruement is past entertaining!
The fact is that manifold vacuum is a function of throttle opening. Any novice piston engine pilot knows this and is responsible for engine management based on this as one of the 3 critical data points of "vacuum", RPM and EGT. Vacuum varies relatively smoothly, albeit non-linearly across the full range of throttle opening.
If you can grasp that and apply that fact to the operation of the fuel pressure regulator, it will become obvious that this variable force is applied to the vacuum diaphram in the FPR in the same continuously variable way that it is created, that being in direct relationship to the throttle opening. That varying force is applied directly to the spring (via the diaphragm) that controls the part of the FPR that you do understand. This throttle dependent force directly affects the force applied by the spring to the fuel restriction orifice, thereby controlling absolute fuel rail pressure proportionally to full range of throttle position.
If you continue to disbelieve this basic truth about vacuum in an air-throttled engine, I recommend that you connect a vacuum guage to the intake manifold (NOT throttle body) of the vehicle of your choice and go out on the road. Note the vacuum readings at idle, and then at steady state speed, in 10 mph intervals, up tp 100 mph. I guarantee you that these vacuum numbers will be different from each other, progressing from somewhere around 18" at idle, downward toward 0" where the throttle is wide open.
Please either learn this or drop it. You have much valuable experience to share here, but this agruement is past entertaining!
02-09-2007, 12:07 PM
#67
Rennlist Member
Thread Starter
Once again, you are falling into the misundertanding trap. i never ever said manifold pressure didnt change with different power setttings. they are intimately related. who, more than me, has talked about varied vauum levels in the intake relating to power levels of the 928 or any engine? remember discussion regarding pressure drop across the intake, air box vacuum levels , ram pressure, volumetric efficiency, etc etc.???
the point you are clearly missing and this is frustrating for you, is that the vacuum driving the "idle fuel pressure pull back pressure" is drawn from the small port on the backside of the throttle plate venturi. if they (engine designers and fuel reg designers) wanted the fuel regulator to be controled by vacumm pressure , like a MAP system works ( by the way, what you described is what a MAP system does, but it doesnt work on the fuel regs it works on the ECU to control injector duration), they would have connected the fuel regs to a port ON the intake manifold. in fact, the small amount of vacuum through the tiny port, doesnt do much pull back of the spring, unless you are at idle. past that , it doesnt do much. the fuel rail pressure control is via the diaphram . If the fuel demands are light, then the pressure on the diaphram, is greater and the return line gets the most amout of fuel running back to the tank. in an extreme case, think about WOT creating 500hp. you may be getting near the max flow capabilities of the fuel pump. at this point, there would be no fuel woud be returing to the tank. but, consider WOT at 2000rpm , same engine. still there is no vacuum in the intake nor at the fuel reg vacuum port, but the fuel pump has pressure and flow to exceed demands. Pressure on the diaphram as caused all the fuel to go to the injector rail. at this point, the return line be closed. What happpens, the pressure of the fuel that is not needed , pushes on the back side of the diaprham, opening the return line to the fuel tank, thus this becomes a self regulating pressure system for the fuel rail. If you don tbelieve this, all you have to do is look at a fuel pressure gauge as said, and blip the throttle , go on a dyno an also removed the vacuum lines to see if anything changes. it doesnt.
If i didnt understand this,and what i said wasnt true, my dyno runs wouldnt have the same fuel air ratios, and my fuel pressure would change at varied throttle positions. it doesnt. when it does change is off idle with the vacuum connnected. with it not connected, idle and WOT pressure is the same.
Manifold pressure is extricably tied to power and mass flow throught the engine. there is no debate there, and if you read my last post regarding this, you would have understood this point.
Mk
the point you are clearly missing and this is frustrating for you, is that the vacuum driving the "idle fuel pressure pull back pressure" is drawn from the small port on the backside of the throttle plate venturi. if they (engine designers and fuel reg designers) wanted the fuel regulator to be controled by vacumm pressure , like a MAP system works ( by the way, what you described is what a MAP system does, but it doesnt work on the fuel regs it works on the ECU to control injector duration), they would have connected the fuel regs to a port ON the intake manifold. in fact, the small amount of vacuum through the tiny port, doesnt do much pull back of the spring, unless you are at idle. past that , it doesnt do much. the fuel rail pressure control is via the diaphram . If the fuel demands are light, then the pressure on the diaphram, is greater and the return line gets the most amout of fuel running back to the tank. in an extreme case, think about WOT creating 500hp. you may be getting near the max flow capabilities of the fuel pump. at this point, there would be no fuel woud be returing to the tank. but, consider WOT at 2000rpm , same engine. still there is no vacuum in the intake nor at the fuel reg vacuum port, but the fuel pump has pressure and flow to exceed demands. Pressure on the diaphram as caused all the fuel to go to the injector rail. at this point, the return line be closed. What happpens, the pressure of the fuel that is not needed , pushes on the back side of the diaprham, opening the return line to the fuel tank, thus this becomes a self regulating pressure system for the fuel rail. If you don tbelieve this, all you have to do is look at a fuel pressure gauge as said, and blip the throttle , go on a dyno an also removed the vacuum lines to see if anything changes. it doesnt.
If i didnt understand this,and what i said wasnt true, my dyno runs wouldnt have the same fuel air ratios, and my fuel pressure would change at varied throttle positions. it doesnt. when it does change is off idle with the vacuum connnected. with it not connected, idle and WOT pressure is the same.
Manifold pressure is extricably tied to power and mass flow throught the engine. there is no debate there, and if you read my last post regarding this, you would have understood this point.
Mk
Originally Posted by BrianG
This is getting ridiculous Mark. The thing that is the most frustrtating is that while you are wrong, you are not uncertain.
The fact is that manifold vacuum is a function of throttle opening. Any novice piston engine pilot knows this and is responsible for engine management based on this as one of the 3 critical data points of "vacuum", RPM and EGT. Vacuum varies relatively smoothly, albeit non-linearly across the full range of throttle opening.
If you can grasp that and apply that fact to the operation of the fuel pressure regulator, it will become obvious that this variable force is applied to the vacuum diaphram in the FPR in the same continuously variable way that it is created, that being in direct relationship to the throttle opening. That varying force is applied directly to the spring (via the diaphragm) that controls the part of the FPR that you do understand. This throttle dependent force directly affects the force applied by the spring to the fuel restriction orifice, thereby controlling absolute fuel rail pressure proportionally to full range of throttle position.
If you continue to disbelieve this basic truth about vacuum in an air-throttled engine, I recommend that you connect a vacuum guage to the intake manifold (NOT throttle body) of the vehicle of your choice and go out on the road. Note the vacuum readings at idle, and then at steady state speed, in 10 mph intervals, up tp 100 mph. I guarantee you that these vacuum numbers will be different from each other, progressing from somewhere around 18" at idle, downward toward 0" where the throttle is wide open.
Please either learn this or drop it. You have much valuable experience to share here, but this agruement is past entertaining!
The fact is that manifold vacuum is a function of throttle opening. Any novice piston engine pilot knows this and is responsible for engine management based on this as one of the 3 critical data points of "vacuum", RPM and EGT. Vacuum varies relatively smoothly, albeit non-linearly across the full range of throttle opening.
If you can grasp that and apply that fact to the operation of the fuel pressure regulator, it will become obvious that this variable force is applied to the vacuum diaphram in the FPR in the same continuously variable way that it is created, that being in direct relationship to the throttle opening. That varying force is applied directly to the spring (via the diaphragm) that controls the part of the FPR that you do understand. This throttle dependent force directly affects the force applied by the spring to the fuel restriction orifice, thereby controlling absolute fuel rail pressure proportionally to full range of throttle position.
If you continue to disbelieve this basic truth about vacuum in an air-throttled engine, I recommend that you connect a vacuum guage to the intake manifold (NOT throttle body) of the vehicle of your choice and go out on the road. Note the vacuum readings at idle, and then at steady state speed, in 10 mph intervals, up tp 100 mph. I guarantee you that these vacuum numbers will be different from each other, progressing from somewhere around 18" at idle, downward toward 0" where the throttle is wide open.
Please either learn this or drop it. You have much valuable experience to share here, but this agruement is past entertaining!
02-09-2007, 12:22 PM
#68
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Originally Posted by mark kibort
Here is absolute proof. why is it, i dont even run my vacuum line on the fuel regulators, yet fuel air ratios are kept constant under varied loads and rpms?
MK
MK
Originally Posted by mark kibort
we all race and drive with this situation and it is not an issue. full lean , to full rich and transient periods in between. this happens in almost all driving situations.
MK
MK
02-09-2007, 02:02 PM
#69
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Thread Starter
well, when you are on and off the throttle, the pressure is constant, but the fuel ratios change based on where they should be for a given power setting. idle near 14.7 ave (it hunts) WOT 12.6:1 and off throttle, greater than 17:1 (full lean, because injectors are shut off, or flow is minimal depending i you use the off throttle fuel cut off switch as i dont)
as far as fuel air ratios , i should have been more clear. those ratios dont change at any particular power setting , with or without the vacuum line attached, except for idle,where the vacuum line pulls back the pressure 5-7psi. at any other throttle setting , it has no measureable effect . thats the point of this part of the debate.
the pressure is constant in all cases, due to the fuel pump running and the pressure being kept constant via the pressure regulator. if you didnt have a regultor, the pressure would go to max fuel pump pressure and go down as demand for fuel increased through the injectors. the regulator keeps the pressure constant, but not via the vacuum line, by the diaphram's interaction with the fuel pressure in the lines and the deman of the injectors, via the amount of fuel released back to the fuel tank.
mk
as far as fuel air ratios , i should have been more clear. those ratios dont change at any particular power setting , with or without the vacuum line attached, except for idle,where the vacuum line pulls back the pressure 5-7psi. at any other throttle setting , it has no measureable effect . thats the point of this part of the debate.
the pressure is constant in all cases, due to the fuel pump running and the pressure being kept constant via the pressure regulator. if you didnt have a regultor, the pressure would go to max fuel pump pressure and go down as demand for fuel increased through the injectors. the regulator keeps the pressure constant, but not via the vacuum line, by the diaphram's interaction with the fuel pressure in the lines and the deman of the injectors, via the amount of fuel released back to the fuel tank.
mk
Originally Posted by blown 87
So which is it?
02-09-2007, 02:23 PM
#70
This is taken from Porsche Fuel System training.
Fuel pressure regulator
The pressure regulator is fitted to the end of the distributor pipe. The pressure regulator is of the diaphragm-controlled overflow type and controls the fuel pressure to a specified value according to engine type and injection system fitted. It consists of a metal housing divided into two chambers by a beaded diaphragm:
a chamber to hold the coil spring that preloads the diaphragm, and a chamber for the fuel.
When the set pressure is exceeded, a valve connected to the diaphragm opens the inlet to the returnline to allow excess fuel to flow back to the fuel tank.
Fuel system pressure (e.g. 3.8 bar)
The spring chamber of the pressure regulator is connected by a tube with the intake manifold of the engine downstream of the throttle. This results in the fuel system pressure being dependent on the absolute pressure in the manifold and the pressure drop across the injection being identical for every throttle valve position; this ensures that the quantity of fuel injected is influenced only by the opening period of the injection valves.
Fuel pressure regulator
The pressure regulator is fitted to the end of the distributor pipe. The pressure regulator is of the diaphragm-controlled overflow type and controls the fuel pressure to a specified value according to engine type and injection system fitted. It consists of a metal housing divided into two chambers by a beaded diaphragm:
a chamber to hold the coil spring that preloads the diaphragm, and a chamber for the fuel.
When the set pressure is exceeded, a valve connected to the diaphragm opens the inlet to the returnline to allow excess fuel to flow back to the fuel tank.
Fuel system pressure (e.g. 3.8 bar)
The spring chamber of the pressure regulator is connected by a tube with the intake manifold of the engine downstream of the throttle. This results in the fuel system pressure being dependent on the absolute pressure in the manifold and the pressure drop across the injection being identical for every throttle valve position; this ensures that the quantity of fuel injected is influenced only by the opening period of the injection valves.
02-09-2007, 02:28 PM
#71
Mark your understanding of the operation of the FPR seems to be based soley on YOUR results from YOUR vehicle. Maybe your system has been modified by someone who did not document it?
02-09-2007, 06:42 PM
#73
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Thread Starter
it seems to be from porsche, general training. the vacuum source for the fuel regulators is not downstream of the throttle body on a 928, its at the throttle plate or throttle body. I wonder if there is a different style of fuel pressure control for which the 911s employ. remember even though 911s and 944s have AFMs, they are different type contol systems. I dont know enough about the other systems to comment. However, i will say, that the vacuum sourse on a 928 does nothign beyond idle. it could be a fine tuning device, based on absolute pressure values that can change at different altitudes as well, but from what ive seen and tested, the vacuum lines dont due much to pull back pressure after idle. if you have a fuel pressure gauge like i do, you can see this pretty clearly. If you want, i can post a youtube video or something. I think scot with his 928 has the vacum like disconnected now as well.
MK
MK
Originally Posted by a4sfed928
Mark your understanding of the operation of the FPR seems to be based soley on YOUR results from YOUR vehicle. Maybe your system has been modified by someone who did not document it?
02-09-2007, 06:50 PM
#74
Rennlist Member
Thread Starter
notice the second paragraph. "when the pressure is exceeded" what is happening, the pressure gets greater than the spring pressure closing the return line alows, and then fuel is bled off to the fuel tank through the return line. this is the way the fuel pressure is kept constant. the vacuum on the other side pulling against that diaphram, pales in comparison to the force of the fuel line pressure. however, at max vacuum, (ie idle) it has an effect, reducing the pressure by opening the return line. under anything but idle, the vacuum is very low. 17"Hg vs 5-10 under part throttle . if it does anything, which ive seen it do very little, it would be an emmisions thing for fine tuniing of the fuel mixture except at WOT, where no vacuum would exsist. the way the pressure can remain constant is that from say, 2000rpm to 6000rpm WOT, there is no vacuum, so why doesnt the pressure vary? because, its self regulated by the injector demand and the fuel pressure on the spring loaded diaphram return line opening.
I think you are reading too much into the training blurb on fuel regulators.
vacuum does pull back the pressure, but only at idle and very light throttle settings.
mk
I think you are reading too much into the training blurb on fuel regulators.
vacuum does pull back the pressure, but only at idle and very light throttle settings.
mk
Originally Posted by a4sfed928
This is taken from Porsche Fuel System training.
Fuel pressure regulator
The pressure regulator is fitted to the end of the distributor pipe. The pressure regulator is of the diaphragm-controlled overflow type and controls the fuel pressure to a specified value according to engine type and injection system fitted. It consists of a metal housing divided into two chambers by a beaded diaphragm:
a chamber to hold the coil spring that preloads the diaphragm, and a chamber for the fuel.
When the set pressure is exceeded, a valve connected to the diaphragm opens the inlet to the returnline to allow excess fuel to flow back to the fuel tank.
Fuel system pressure (e.g. 3.8 bar)
The spring chamber of the pressure regulator is connected by a tube with the intake manifold of the engine downstream of the throttle. This results in the fuel system pressure being dependent on the absolute pressure in the manifold and the pressure drop across the injection being identical for every throttle valve position; this ensures that the quantity of fuel injected is influenced only by the opening period of the injection valves.
Fuel pressure regulator
The pressure regulator is fitted to the end of the distributor pipe. The pressure regulator is of the diaphragm-controlled overflow type and controls the fuel pressure to a specified value according to engine type and injection system fitted. It consists of a metal housing divided into two chambers by a beaded diaphragm:
a chamber to hold the coil spring that preloads the diaphragm, and a chamber for the fuel.
When the set pressure is exceeded, a valve connected to the diaphragm opens the inlet to the returnline to allow excess fuel to flow back to the fuel tank.
Fuel system pressure (e.g. 3.8 bar)
The spring chamber of the pressure regulator is connected by a tube with the intake manifold of the engine downstream of the throttle. This results in the fuel system pressure being dependent on the absolute pressure in the manifold and the pressure drop across the injection being identical for every throttle valve position; this ensures that the quantity of fuel injected is influenced only by the opening period of the injection valves.