C5 fuel system gurus
Thread Starter
Le Mans Master
Joined: Dec 2003
Posts: 5,047
Likes: 252
From: San Diego
C5 fuel system gurus
Ok I've install a custom fuel system on my C5 for my added power. Now, I'm using a Aeromotive pump with - 10 line form the drivers side tank and using my old feed line as a return line. I'm having problems with the right side tank pumping over to my left hand tank. I've studied the GM manuals I have and it shows that the left tank has a jet pump that pumps over to my right hand tank. Now that I'm running a external pump it's not providing pressure to the jet pump from the left tank to level my fuel out. Has anyone encountered this problem with a custom fuel system with a external pump? Oh also I have all of the feed lines and crossover lines hooked up from the left tank to the right tank if the explains alittle more. Any knowledge would help me out alot 
Burning Brakes
Joined: Mar 2005
Posts: 822
Likes: 1
From: Henderson Texas
I have a similar problem...with a few differences. I have an identical fuel system with an external pump, but I also added 96lb. low impedence injectors. I then turned the fuel pressure down to compensate for the larger injectors and to make it easier to tune. In doing so I guess dropping the pressure caused the jet pump not to work correctly and will not let me fill the car over half of a tank. The fuel gauge still shows full, but there is actually only fuel in the drivers tank. As soon as I get to half empty on my gauge the car runs out of gas and dies. I spoke to lingenfelter the other day and they make two little fuel pressure block offs that bypass the factory fuel pressure regulators in both tanks and should allow me to run at a lower pressure and use both tanks. I don't know if any of this is beneficial to you or not, but it is all I know. You didn't mention what year your car was, but using context clues I am guessing it is a 03 or up with the FFS system like mine.
This may also be helpful...
http://www.corvetteactioncenter.com/...el+Tank+System
This may also be helpful...
http://www.corvetteactioncenter.com/...el+Tank+System
Thread Starter
Le Mans Master
Joined: Dec 2003
Posts: 5,047
Likes: 252
From: San Diego
well the problem is that when I get around half tank my gauge goes to empty. I think I might tap my right hand tank with a -10 fitting and run it to the suction side of my fuel pump.
Thread Starter
Le Mans Master
Joined: Dec 2003
Posts: 5,047
Likes: 252
From: San Diego
That could be the case, when this problem first happened to me I was on a full tank then when it passed the half tank mark it went to empty. I still drove on it for about 40 plus miles with no issue. So I thought my jet pump from the left tank was not feeding my right tank. When I made the mod to my sending unit I left the float of level indicator as is so this may be the problem.
Last edited by Brandon619; Jan 27, 2009 at 01:20 PM.
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Pro
Joined: Feb 2005
Posts: 652
Likes: 16
From: Upton MA
I tried doing a boost referenced system on my late 03 Z06. I have a bosch internal pump and a Walbro ext. The system is a return system. All has worked fine for a couple of years, 800+rwhp. When I decided to up in injector size and change over to a boost referenced system, I ran into some problems. I turned down the pressure regulator and boost referenced the regulator. When there is less than 45-50 lbs pressure the siphon pump stops working, hence the gas from the passenger side does not transfer to the drivers tank. Turning the fuel pressure back to 58 psi and not boost referencing corrected the problem.
Advanced
Joined: Aug 2004
Posts: 99
Likes: 0
If your aero pump is external that it won't work period, as the siphon pump isn't getting any pressure from an external pump. Since you are using the feed line as a return line then I don't see how it can work at all, since the siphon pump gets its pressure from the supply line. In the later model vette this is all occurring inside the tank itself, so without knowing more about your system I would say it just plain won't work.
Iif you don't want to redo your fuel system to work with the stock internal bucket and lines - build a crossover line at the bottom of the tanks. You cannot do what you said, which is add a feed line from the pass tank to your aero pump because as soon as one tank goes dry the pump will starve. I know its counter intuitive, you would think the tank with the fluid would have a pressure head and this would feed the pump instead of the dry tank, but instaed the pump sucks from the easiest source which is the empty tank.
So a crossover line is probably your best bet. Unless I misunderstand what you have done, but what I envision is no in tank pump and simply a feed line into your external aero pump.
Iif you don't want to redo your fuel system to work with the stock internal bucket and lines - build a crossover line at the bottom of the tanks. You cannot do what you said, which is add a feed line from the pass tank to your aero pump because as soon as one tank goes dry the pump will starve. I know its counter intuitive, you would think the tank with the fluid would have a pressure head and this would feed the pump instead of the dry tank, but instaed the pump sucks from the easiest source which is the empty tank.
So a crossover line is probably your best bet. Unless I misunderstand what you have done, but what I envision is no in tank pump and simply a feed line into your external aero pump.
Advanced
Joined: Aug 2004
Posts: 99
Likes: 0
I spoke to lingenfelter the other day and they make two little fuel pressure block offs that bypass the factory fuel pressure regulators in both tanks and should allow me to run at a lower pressure and use both tanks.
This is important because if you remove that regulator, then you no longer have to keep your base fuel pressure so high, which is beneficial to people running boost. If you require your base pressure under motor running high vacuum conditions to be 58 psi for fuel transfer to cocur, that means your static pressure with engine off needs to be about 65 psi, which means under 15 psi of boost you have 80 psi fuel pressure, which is obviously much harder for the fuel pumps to meet the flow requirements.
Can anyone tell me why the 2nd regulatro before the siphon pump is used ?
Thread Starter
Le Mans Master
Joined: Dec 2003
Posts: 5,047
Likes: 252
From: San Diego
Good point preston, I think I have two options the first one is a long shot. Inside the right tank where the jet pump is a check valve I was hoping if I removed it both tanks would just levels out? The second one is to just run a -10 line from that tank to the suction side of my pump. I just want to get all the info I could before ripping into the other tank.
Pro
Joined: Jan 2002
Posts: 741
Likes: 9
From: Rancho Cordova CA
Just an idea
I run a Y block (pump in 8, out 8 and 6 to pass tank) with a filled 6 AN fitting that I drilled out to feed the surge pump on the Pass side. I measured the small hole in the stock plastic Y and drilled out my replacement Y fitting. If you lower your pressure perhaps a larger hole will allow additional fuel to flow to properly work the surge pump? I am no mathematic genus but if you decrease pressure say 10% from stock perhaps a 10% larger hole?
Thread Starter
Le Mans Master
Joined: Dec 2003
Posts: 5,047
Likes: 252
From: San Diego
I run a Y block (pump in 8, out 8 and 6 to pass tank) with a filled 6 AN fitting that I drilled out to feed the surge pump on the Pass side. I measured the small hole in the stock plastic Y and drilled out my replacement Y fitting. If you lower your pressure perhaps a larger hole will allow additional fuel to flow to properly work the surge pump? I am no mathematic genus but if you decrease pressure say 10% from stock perhaps a 10% larger hole?
Advanced
Joined: Aug 2004
Posts: 99
Likes: 0
I'm close to just tapping a -10 fitting from the pass sending unit or access hole and running it to my pump.
Your best bet is to tee a -6 line off the pump OUTLET, and run that intot he passenger tank to drive the jet pump. Put an old carb jet in there as a restrictor, not sure what size but you're looking at ~.045 hole stock. Actually this restrictor might not be required since the jet pump already has a pinhole orifice. You'll need a 5/16" hose barb to 3/8 npt, a double female npt coupler, and a 3/8npt to -6 hose inside the tank to connect to the stock jet pump hose. . Also, you must use teflon SS line or some other type of fuel immersion hose once you are insie the tank itself. Look for aeroquip teflon fittings and hose at summit, Summit has them up to -8 now. In fact all braided AN type hose that handles fuel should be teflon if you don't want it to weep a smell. You could also transition from -6 to fuel hose at the bulkhead inteface, however you want to do it.
Le Mans Master
Joined: Feb 2009
Posts: 5,169
Likes: 199
From: Your Sister's Bedroom
Ok, toss me some insight here.
I am in the process of trying to unscrew a 2002 Z06 corvette that belongs to a friend and was hacked up by some fool.
Anyways, the old fuel system was two in tank 340 pumps, modified factory fuel hat with two -6 lines coming out of it to a y block and into one -8 line that ran up to the fuel rails then to a regulator and back to the tank. On that block, there was another discharge line that went to the siphon pump in the right tank. It worked, it transferred fuel. Problem was, because of that line running off the fuel supply y block the fuel pressure would fluctuate nearly 10psi at the rails because of that bleed off. This is not acceptable. I have no re-routed the system. I removed the fitting from the y block and plugged it. So now the supply goes to the rails and no where else. Then I took the return line that was running to the tank and ran it to the siphon pump. Now my question is, with a static 60psi at the rails and under boost creeping to 80psi will the pressure coming off the return have enough power to power that siphon pump? If not, I need a fix for this.
I am in the process of trying to unscrew a 2002 Z06 corvette that belongs to a friend and was hacked up by some fool.
Anyways, the old fuel system was two in tank 340 pumps, modified factory fuel hat with two -6 lines coming out of it to a y block and into one -8 line that ran up to the fuel rails then to a regulator and back to the tank. On that block, there was another discharge line that went to the siphon pump in the right tank. It worked, it transferred fuel. Problem was, because of that line running off the fuel supply y block the fuel pressure would fluctuate nearly 10psi at the rails because of that bleed off. This is not acceptable. I have no re-routed the system. I removed the fitting from the y block and plugged it. So now the supply goes to the rails and no where else. Then I took the return line that was running to the tank and ran it to the siphon pump. Now my question is, with a static 60psi at the rails and under boost creeping to 80psi will the pressure coming off the return have enough power to power that siphon pump? If not, I need a fix for this.
Advanced
Joined: Aug 2004
Posts: 99
Likes: 0
No, the siphon pump needs pressurized fuel and the return line shouldn't have pressure in it. People have been saying it needs 58 psi to work properly but I was just out testing one literally today and it transferred quite a bit of fuel as low as 42 psi. However while I am using the stock pump, check valve, and regulator, the rest of my system is not stock and may operate differently than a stock fuel system.
The point is that fuel coming from return line shuoldn't have any pressure and wno't drive the jet pump.
But in this case you may have bigger problems than that - AS I understand it you connected the primary return line from the front mounted regulator to the siphon pump inlet ? That seems to me like your virtually deadheading the pump as very little fuel flows through the jet pump. I would think if you actually connected it like this your primary fuel pressure would shoot way way up . You'll have to explain better what you did because the car would not run like this.
The way it was connected in the first place seems correct to me, it should not have resulted in 10 psi fluctuations at the rail. Perhaps you ahve a leak that only shows up under higher pressure ? That's how my system is ran - a -8 line off each pump to an intank y-block with a 1/8 npt port feeding a -6 line that attaches to the jet pump with a bunch of adapters, and a -6 transfer line back to the first tank. Another -8 comes out of the y-block and goes to the engine. I do not see any pressure fluctuations. The jet pump has a tiny feed orifice and an inline regulator, it should not be bleeding off any significant amount of fuel, not enough to create pressure swings of 10psi.
The point is that fuel coming from return line shuoldn't have any pressure and wno't drive the jet pump.
But in this case you may have bigger problems than that - AS I understand it you connected the primary return line from the front mounted regulator to the siphon pump inlet ? That seems to me like your virtually deadheading the pump as very little fuel flows through the jet pump. I would think if you actually connected it like this your primary fuel pressure would shoot way way up . You'll have to explain better what you did because the car would not run like this.
The way it was connected in the first place seems correct to me, it should not have resulted in 10 psi fluctuations at the rail. Perhaps you ahve a leak that only shows up under higher pressure ? That's how my system is ran - a -8 line off each pump to an intank y-block with a 1/8 npt port feeding a -6 line that attaches to the jet pump with a bunch of adapters, and a -6 transfer line back to the first tank. Another -8 comes out of the y-block and goes to the engine. I do not see any pressure fluctuations. The jet pump has a tiny feed orifice and an inline regulator, it should not be bleeding off any significant amount of fuel, not enough to create pressure swings of 10psi.
Le Mans Master
Joined: Feb 2009
Posts: 5,169
Likes: 199
From: Your Sister's Bedroom
No, the siphon pump needs pressurized fuel and the return line shouldn't have pressure in it. People have been saying it needs 58 psi to work properly but I was just out testing one literally today and it transferred quite a bit of fuel as low as 42 psi. However while I am using the stock pump, check valve, and regulator, the rest of my system is not stock and may operate differently than a stock fuel system.
The point is that fuel coming from return line shuoldn't have any pressure and wno't drive the jet pump.
But in this case you may have bigger problems than that - AS I understand it you connected the primary return line from the front mounted regulator to the siphon pump inlet ? That seems to me like your virtually deadheading the pump as very little fuel flows through the jet pump. I would think if you actually connected it like this your primary fuel pressure would shoot way way up . You'll have to explain better what you did because the car would not run like this. Do you have any photos of your fuel system?
The way it was connected in the first place seems correct to me, it should not have resulted in 10 psi fluctuations at the rail. Perhaps you ahve a leak that only shows up under higher pressure ? That's how my system is ran - a -8 line off each pump to an intank y-block with a 1/8 npt port feeding a -6 line that attaches to the jet pump with a bunch of adapters, and a -6 transfer line back to the first tank. Another -8 comes out of the y-block and goes to the engine. I do not see any pressure fluctuations. The jet pump has a tiny feed orifice and an inline regulator, it should not be bleeding off any significant amount of fuel, not enough to create pressure swings of 10psi.
The point is that fuel coming from return line shuoldn't have any pressure and wno't drive the jet pump.
But in this case you may have bigger problems than that - AS I understand it you connected the primary return line from the front mounted regulator to the siphon pump inlet ? That seems to me like your virtually deadheading the pump as very little fuel flows through the jet pump. I would think if you actually connected it like this your primary fuel pressure would shoot way way up . You'll have to explain better what you did because the car would not run like this. Do you have any photos of your fuel system?
The way it was connected in the first place seems correct to me, it should not have resulted in 10 psi fluctuations at the rail. Perhaps you ahve a leak that only shows up under higher pressure ? That's how my system is ran - a -8 line off each pump to an intank y-block with a 1/8 npt port feeding a -6 line that attaches to the jet pump with a bunch of adapters, and a -6 transfer line back to the first tank. Another -8 comes out of the y-block and goes to the engine. I do not see any pressure fluctuations. The jet pump has a tiny feed orifice and an inline regulator, it should not be bleeding off any significant amount of fuel, not enough to create pressure swings of 10psi.
The fuel return line has approximatly 30psi of of fuel pressure on the return side from what I can tell at normal operating load. But if your saing it takes nearly 60psi to power the siphon so I guess I will have to look back into this further.....
Last edited by breecher_7; Feb 2, 2009 at 06:54 AM.