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Discussion Starter · #1 ·
Hello all. I had a difficult time getting 80# injectors to idle decent using E85. I decided to run a return style system to lower the idle fuel pressure making less pressure on the injectors and getting it to idle smooth. I was unhappy with the results by changing the injector settings alone to get the injector pulse width small enough for a nice idle. With a bigger injector the ECU's injector driver struggles to fire the injector fast enough which ends up making the car idle choppy and usually rich.... To do this you will also need a way to modify the ECU such as HPTuners. The car runs great and idles perfect now. I am VERY HAPPY with the results. Some people can get bigger injectors to have a tolerable idle but I think a return style system is a better route. *** DISCLAIMER*** this is how I built my system. I am not responsible if attempt this and have bad results or blow something up.


Here's my parts list.
I decided to go with -6AN for the hose and fitting size. Its close to the 3/8" size of the fuel feed.

Misc Items: Zip ties and vacuum T

Hardware from Summit Racing:
AER-FBM2872 STEEL 3/8 BRAZE/#6 FLARE - $5.95 (1)
SUM-220166B -6 O-RING TO -6 FLARE FIT BLK - $6.95 (2)
SUM-220631B -6 PLUG O-RING BLK - $1.95 (1)
SUM-220637 -06 BULKHEAD UNION - $3.95 (1)
SUM-220687B -6 90 DEGREE BLACK HOSE END - $11.95 (3)
SUM-220690B -6 STRAIGHT BLACK HOSE END - $3.95 (1)

Hose from an Ebay Store:
-6 AN Braided Stainless Steel Fuel Line Hose 1500 PSI | eBay

You will need about 12 to 13 foot. Depending on where you want to mount the regulator.

Fuel pressure gauge from an Ebay Store:
Marshall 0-100 PSI Fuel Pressure Gauge 1.5 Black 15029 | eBay

Adjustable fuel pressure regulator from an Amazon store:
Amazon.com: Aeromotive 13129 Compact -6 EFI Fuel Pressure Regulator: Automotive

I went with the Aeromotive compact EFI regulator to save space. You can pretty much use any regulator with a boost reference port. I'd recommend getting a good name brand one.



You may also want to get a higher volume fuel pump while you are at it. I did not since mine was able to keep up with the demand of my setup.

You may also want to get a inline fuel filter since you cannot use the one in the tank. I got a mesh screen one from the auto parts store. Its part # is F29160 - Purolator. 2 high pressure hose clamps or ear clamps are needed too.

Another thing you may want to get is a LSJ fuel rail from an ION redline or Chevy colbalt since it is easier to modify to a return system.

Once you have all the stuff you need...
Step 1: Remove the trunk liner. It pretty much just sits in there. Dont forget to remove the convertible top drain tubes, elastic cords on the side and unplug the trunk light. If you are unfamiliar with dissembling the trunk you can look at the free shop manuals on line using Autozone's website. Put the liner in a safe location like a boat.:jester:



Step 2: Remove the metal access cover. Take out the 7mm screws and pry up gently with a screwdriver. This will give you access to the pump housing and the top of the fuel tank.


Step 3: Disconnect the fuel hoses and connectors. You may want to relieve the fuel pressure via the schrader valve on the fuel rail. No special tools need for hose removal. Most just push on the tab and pull off. The big hose next to the fuel line probably wont move enough to be fully disconnected. Just loosen it up for right now.

Step 4: Remove outer fuel tank ring. This is a challenging part. It took a little bit of time for me to get this sucker to move. I have seen people use an air chisel but, that didn't work for me so I use a prybar and hammered the tabs counterclockwise.


Step 5: Pull up slightly and back to the rear left side of the car. This should give you enough room to get that hose off. Once the hose is off then pull up but make sure you do not damage the fuel gauge float. At this time also you may want to drain the gas out of the sending unit by tipping it slightly to the side.

Step 6: Disconnect the 2 fuel hoses off the metal in tank filter. As you can see the pump sits in the center of this goofy filter. The stock fuel pressure regulator is also part of the filter so that will need to be removed. You can remove the stock filter and regulator or keep it in place. I decided to just keep it in there to make sure everything stays in place. This would also be the time to remove the stock pump if you are upgrading it.



Step 7: Bulkhead installation. Find the center of sending unit. There is enough room for the bulk head and the nut to fit. Make sure you check the bottom side of the lid so you do not drill into anything and you allow enough room for the bottom nut. I used a 1/2 " drill bit and threaded the bulk head into the plastic, then I secured the bottom side with a nut. You may also want to add an O-ring or some kind of thread sealer at this point. Remember, no hose or anything extra is needed to connect to the bottom side of this bulkhead since fuel is just getting dumped back into the tank.

 

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Discussion Starter · #2 ·
Step 8: Installing fuel filter. Here's were you can get creative. I just wanted to do this as easy as possible so I connected the "in" port on the filter to the fuel pump hose and the out to the sending unit lid (stock fuel line connector), secure with a high pressure clamp.



Step 9: After cleaning everything up you can put the sending unit back in the tank (make sure you be careful with the fuel gauge float!), install the lock ring and hoses.

Step 10: Remove the fuel rail. take off the injector harness connector, map sensor connector and fuel line. There is a special tool to remove the quick connect fuel hose. I cut a marker into a 1" section and slit it down the side. You push it into the fingers on the hose end and it releases the tabs to pull the line off. Take the (2) 10mm head bolts off to remove the rail. You should be used to this already if you installed larger injectors.



Step 11: Fuel rail return fitting. If you are using the stock rail, drill a 3/8" hole above injector #1. Clean the rail and make sure all the gas is gone before welding the fitting over the hole. If you are using an LSJ rail, remove the stock regulator and install the fitting on the end of the rail. It is very important to check for leaks. Plug all the ports with a cork or rubber plug/ cap. Add a couple psi of compressed air into rail and use soapy water to check for leaks. If its not bubbling.. you are good to go!:thumbs:

 

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Discussion Starter · #3 ·
Step 12: Re install the fuel rail, injectors and connectors.

Step 13: Mount the regulator. I found a good location on the left side of the engine bay. I ended up mounting it to my catch can.

Step 14: Make a fuel hose to go from the fuel rail fitting to the side of the regulator (read regulators user guide to make sure you have the right "infeed" port). I chose to loop mine in a "U" shape. Make sure you also plug up any other "infeed" ports on the regulator.


Step 15: Make a hose from the "exit" port on the regulator to the bulkhead on the fuel sending unit. I ran mine under the car following the fuel and brake lines. I used cable ties (zip ties) to secure them to the line holder brackets. You can use plastic wire holders and drill them to the car if you'd like... I didn't like the idea of drilling into the car.

Step 16: Add a vacuum hose to the new fuel pressure regulator. I used a vacuum "T" and tied it into the same line as the blow off valve. Any small vacuum line that gets full intake vacuum and boost pressure will work.




Step 17: Tighten up all the hose ends snug. At this point you can connect the battery back up if you disconnected it. Turn the key on "RUN" or as they call it KOEO (key on engine off). This should build fuel pressure. Check for leaks.

Step 18: Once you verified that there isn't any leaks and everything is connected, Re install the metal cover and trunk liner.

Step 19: Now since everything is done mechanically its time to change the ECU so it doesn't use the MAP sensor and voltage offset to control the fuel pressure. A good "How to" on this can be found here: How to tune for return fuel system. - HP Tuners Bulletin Board

Basically the first thing you need to know is what base fuel pressure you want to run. I ran 30 PSI for 80# injectors and it worked great. I used 40 PSI for 60# injectors on a friends car and that worked great also. You can play around with what works best for you but it needs to be set correctly in the ECU.

Using the data from the injectors you have or the Omega Injector Spreadsheet, find the column that is the PSI you set for your base pressure and paste it for every column in the table like I did here:

Do this for the "offset vs. volts vs MAP" and "offset vs press vs IGNV".

Next change the table called "injector flow vs pressure delta" to 63.5 across the board like (SJSchafer) did here


Also change your "injector flow rate modifier vs battery voltage" to 1.00 across the board.

Save this and flash your ECU.

Step 20: Start up the car and adjust the fuel pressure regulator to your base PSI you chose. (Follow the fuel pressure regulator user guide for this)

Step 21: Do a MAF tune and it should be good to go!:thumbs:
 

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Love this write up. I know this is a VERY old thread but in the hopes someone here may know the answer, is there any welding required if you us the LSJ rail? would be something I'd do if I didn't have to weld. I can't weld. Would love to have a return fuel system though...maybe run a better fuel pump...
 

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Discussion Starter · #11 ·
Yes, to use the stock rail you will need to weld the rail. If you could find an older rail that has a return port that would work. I looked all over when I did this upgrade and I couldn't find a rail that was an easy replacment. I also have thought about buying or building a bigger dia rail in the future.
 

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You don't need to weld to have a return system.

Do almost exactly what he did, but instead of welding the fitting on, just run a regulator "inline" with the fuel rail.




The OP did the top version, but the bottom version works just as well. It's easiest to intercept the 3/8 fuel line underneath the car before it turns into nylon braided flex hose. You will want to use Swagelok SS-600-6-6AN fittings (no special tools needed) or a 37* flaring tool and -6 tube nuts. This will let you run the hard line to braided hose, braided hose to the regulator, regulator to braided hose again, and the braided hose to the fuel rail. The fuel rail can be adapter by using a 3/8 to -6 GM rail adapter. You'll want to pick one of the manufacturers that make the locking adapters such as the aeroquip ones:



I also think the OP would have been much better off using the stock filter that sits inside of the tank, it's actually fairly big.

This can all be done with the tools in your garage, except for maybe that ridiculous hard to get off fuel tank ring (OTC 6599 ~$40)
 

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Hmmmm...

Correct me if I'm wrong LT1 (and I suppose I am) but I always thought the benefit of a return system was that all the injectors in the rail got the same fuel pressure because the fuel is allowed to travel through the whole rail before returning the excess pressure "Bleed off" to the tank?
 

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You supposed right! You can think of the stock system as a return system, except it returns inches from the fuel pump with a ball and spring. The return never technically leaves the tank so it's always metered right at the pump.

Now for some math:

fluids are subject to p=r*g*h : r is rho (density), g is acceleration (usually gravity) and h is the difference in height. When we're talking about a return style system, there isn't a pressure difference between the regulated pressure in the tank and the fuel rail because there isn't a difference in height. This is looking at the car from top to bottom.

Now here's why it matters. When a car accelerates or brakes, it's producing positive and negative acceleration forces or (g's), usually in the magnitude of 0-1 for a normal car. Now the "h" in that equation starts to matter because the acceleration forces are lateral now. This means that if there is a length difference of 12 feet from the tank (the spot at which it's regulated) and the fuel rail (the point at which pressure matters) then we're looking at a pressure difference.

Gasoline @ 60* has a rho of 711kg/m^3
Assume .5G positive acceleration .5(9.81/2 m/s^2)
Assume a distance of 12 feet from the gas tank regulator to the fuel rail (3.6 meters)

deltaP=711kg/m^3 * 1/2(9.81 m/s^2) * 3.6 meters
deltaP=25.08408kPa or 3.63 psi.

This means that if the stock regulator is set for 410kPa (59.46 psi) then the front of the car will only see 55.83 psi when you're accelerating at 4.9m/s^2. The exact opposite would happen when you're braking (higher pressure in the rail than the regulator).

By moving the regulator to the same "h" as the fuel rail (or next to the fuel rails) then you can always have a consistent pressure. The fuel rails should have the same pressure just before the the fuel enters the fuel rails, and throughout the fuel rail itself (unless the fuel line or fuel rail is a restriction). 700+hp can be made on -6 hose so I don't think the typical LNF guys are anywhere near this restriction.

Hmmmm...

Correct me if I'm wrong LT1 (and I suppose I am) but I always thought the benefit of a return system was that all the injectors in the rail got the same fuel pressure because the fuel is allowed to travel through the whole rail before returning the excess pressure "Bleed off" to the tank?
 
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