Overview

This research is based on the evaluation of the fuel delivery system of a 1993 Eagle Talon AWD.  The general premise is that the stock fuel delivery system provides inadequate fuel flow for the high performance modified 4G63 engine.  This paper covers the reasoning behind the premise and the procedure to create a SteveTek High Flow Fuel Delivery System. 

Background

As we look to get more power from our engines, we naturally want to get a greater air/fuel charge through the system.  Lets consider how to increase fuel.

One common method to supply more fuel to the engine is to increase the pressure at the fuel pump by increasing the voltage.  This definitely increases the pressure at the pump, but that doesn't necessarily translate to more volume at the fuel rail. This is because the whole system was designed to deliver the volume of fuel that the stock injectors need, and not much more.  The same analysis holds for installing a high flow pump.  The fact is that you can only push so much fuel through the 'coffee straw' stock system. Its a capacity problem.

With the help of a local performance shop with a liquid flow bench, I was able to run some flow tests on the stock fuel delivery system.  It was found that from the fuel pump outlet to the fuel rail inlet fitting, @ 60psi, a flow of 1.9 liters per minute could be measured.  When the pressure was increased to 75psi, the flow only went up by 0.1 lpm.  That's only ~5% more flow for a 25% increase in pressure... not good.    Couple that with the fact that stock injectors are 450 cc/m so that four of them can approach a flow of 1.9 lpm (4 x 450) , it can be seen that we are approaching the point where the injectors can outflow the fuel system.

What are the reasons for this low flow?  There are several restrictive points in the system.  Starting from the front and working back, they are:

• The fitting at the fuel rail only has a diameter of 5.5mm
• The banjo fitting at the outlet of the fuel filter. 
• Fuel filter is a low-flow design (2 lpm).
• The steel fuel line is only 3/16" ID.   [BTW: the -6AN fitting we'll be using has an actual measured ID of 5/16"]

After market pumps can develop a lot of pressure though, so what's the problem?  One significant issue is based on how we tune our cars air/fuel ratio.  Notice in figure 1 that in this case the fuel pressure sender is in the small diameter restrictive section of the delivery system.  Now the diameter of the fuel rail is much larger than the fuel line leading up to it.  So when the injectors are at a high enough duty cycle as to approach the maximum capacity of  the preceding delivery system, the pressure in the fuel rail will see a drop off at each successive injector as indicated by the wavy blue lines.  There will be enough pressure to deliver sufficient fuel for the first two cylinders and probably the third.  But the last cylinder (#1) will be starved and thus risks a lean condition. 

Since the EGT is usually tapped to the #1 runner, a  lean condition is indicated by a high temperature in that cylinder.  But typically, an 02 reading is also used to tune and the O2 value we see is based on all four cylinders.  Hence we have been accustom to thinking that our lean threshold is much higher ( > .85V) than it needs to be. And our fuel pressure gauge has not given us a proper indication of the problem as it is far upstream and is not subject to the pressure drop off in the rail.  It would be better to mount the fuel pressure sender at the end of the rail but that would be a difficult installation.

It is asserted that this leads to a loss of power because we effectively have two very rich cylinders, one about right and one lean.  Because we have to protect the lean cylinder, we sacrifice power in the first two.  The fuel pressure regulator also does not help alleviate this problem. Since it is at the end of the rail, it can only regulate the maximum pressure provided there is enough flow.  It does nothing to correct the low pressure, low flow situation.

The solution is to upgrade the flow capacity of whole fuel delivery system to minimize the pressure differential seen by all four injectors. Or, put another way, a high flow pump and big injectors are great. But you've got to have big enough line to actually get the extra gas to the intake.

After the new fuel delivery system was designed and built, we took it back to the flow bench and found that it flowed  ~10 lpm @ 60psi. Very nice :-)

A word of caution: The following procedure is pretty involved and is not recommended for those without a reasonable amount of mechanical knowledge and automotive repair experience.

Parts, Tools & Supplies List

Procedure

There are three main parts to the procedure: 1) Disassembly & stock system removal, 2) Assembly of new hoses and fittings & machining the fuel rail, and 3) Routing new lines and installing new assemblies. The diagram below is the basic plumbing hookup for the system. Use it as a guide while following the instructions further down.

Since this project is meant as a 'do it yourself' mod, we aren't selling kits anymore. If you need assistance getting your rail machined, please drop us a line so we can arrange to give you a hand.

Disassembly & stock system removal
	1.  First, you'll need to relieve the fuel pressure in the system. In the hatch, pull back the carpet on the drivers side. Disconnect the fuel pump wiring harness pictured. Start the car and give it some throttle until it dies.
	2.  Disconnect and remove the battery and the battery box.  Remove the upper IC pipe and throttle body elbow. Now you can see the fuel filter (pictured). Have a couple of shop rags ready to catch any remaining fuel then *disconnect the fuel line (B). You'll need two wrenches. One on the banjo fitting and another one on the top of the fuel filter. Now remove the two bolts holding the bracket (C). Finally, using two wrenches again, disconnect the filter from the steel line below (A). Its a little easier to get to the bottom fitting if you pull the line up a little to give you better access.  Unless you are going to try and salvage the steel line, you don't have to be too worried about bending it up.  Both the banjo bolt and bottom fitting can be very hard to remove.  You may need to soak them in penetrating oil prior to removal
*If the engine is out of the car, you can skip disconnecting the old  filter from the steel line as it would be preferable to remove the stock line and filter as one unit from the car. With the engine still in the car however, it is very difficult to get to all the the line cluster clasps needed to remove the steel line.
	...After the fuel filter is removed. Note: leave this part of the filter bracket (pictured) on the firewall. Remove the filter from the other part of the bracket. Retain the bracket and all bolts as we will be using it to install the new filter later. Look at how tiny the inner diameter of the old fuel line is!
	3.  Remove the throttle body bracket.  This bracket will later be machined to make room for the new fuel fittings.
	4.  Remove the two bolts holding the rail fitting in place and pull the old fuel line out. Discard the old fuel line.
	...After removal of the old fuel line. The end of the fuel rail will be drilled and tapped to accept a new AN fitting. Now would also be a good time to remove the EGR valve and install a blockoff plate (lower arrow).
	5.  Next we need to remove the fuel rail.  Click on the image for a bigger clearer pic. Start by removing the three bolts (A). These also hold down the cables for the cruise control which you should bend back out of the way. Next, disconnect the PVC hose (C). Now you can unseat the rail. Pull it and the injectors out just until they are clear of the head to give yourself some room to disconnect the injector harnesses. Using a small flat blade screwdriver, for each injector connector, carefully pry the wire clip to the side of the connector (B) and disconnect the injector. Make sure you keep track of the wire clips but be aware that you'll probably break the little plastic holder on the bendix connector (which is ok).  Unclamp and remove the fuel return line and the vacuum line (D). Pull the rail clear then remove the injectors and put them in a clean area. Fuel injectors are expensive and somewhat fragile so be very careful not to drop or abuse them. Lastly, remove the fuel pressure regulator from the end of the rail and set it aside.
Assembly of new hoses and fittings & machining the fuel rail
	6.  Take a look at the schematic. We are going to build the 'B' hose that runs from the fuel pressure sender adapter to the fuel rail. This will consist of a straight connector, a 22" length of stainless steel braided line and a 45° connector. First, a few words about working with AN connectors and braided line.  If you are not familiar with these components, click here for a brief tutorial. 7.  Once the 'B' line is done, assemble the 'A' line. We have found that if you start with 15' of line and use 22" of it to make the 'B' line then you will need to cut off about a foot of the remaining line.  If my math works out, that means our 'A' line is about 12'2" long. The issue here though, is that there are multiple ways to route your line so we recommend that for the 'A' line, just attach a straight connector to one end and cut the other end to length once you've routed the line up to the new fuel filter.
	8.  Assemble the swivel coupler, fuel pressure sender adapter and 'B' hose. Do not use teflon tape on any flair end but do use it to seal  NPT connections (in this instance that's only the 1/8 NPT fuel pressure sender). We strongly recommend installing a fuel pressure gauge while upgrading the fuel delivery system.  Discard the fuel filter clip. Temporarily fit the coupler onto the top of the fuel filter.  Set this sub-assembly aside for later.
	9.  To install the K&N filter in the stock bracket we need to cut a 1" x 6" strip of rubber to use as a spacer. We use 1/16" gasket sheet rubber.
	10.  Wrap the fuel rail in a shop rag and then secure it in a vise with the input side up. Using an 11/16" bit, drill out the end of the rail approximately 1 1/2" into the rail. Be careful to align the drill prior to starting this operation to ensure that the passageway stays coaxial with the rail. We find it helpful to 'spin up' the drill prior to engaging the material as otherwise it will tend to bind up.
	11.  Next, cut the threads in the rail with a 3/4-16 tap. Notice how close the original rail size is to the -08AN size!
	UPDATED STEP! 12.  Now we need to affix the -08 to -06 flair union reducer fitting to the rail. Mix up a small quantity of JBWeld as per the package directions on a piece of cardboard (you'll need a dollop about the size of a half dollar).  Then spread the threads of the fitting as well as the threads of the rail with  the JBWeld. Be careful not to glop too much on or it could obstruct the orifice inside the rail.  Next, insert the fitting and screw it down. Don't over tighten or you'll squeeze out too much of the JBweld which is providing the seal.  Just a little past hand tight should do it. With a rag, clean up any overrun around the fitting. IMPORTANT: You must let the JBWeld cure undisturbed for at least 24hrs or you run the risk of a fuel leak.
Routing new lines and installing new components
	13.  Jack up the car and put it up on four jack stands so you can get to all the underbody areas (You can also use two jack stands and do half the car at a time). Remove the fuel tank access panel in the hatch (pictured). Disconnect the stock fuel line. Be aware that this fitting is known to be quite a bear to get loose!  Again, you may want to soak it in penetrating oil. We usually have to use a huge pair of channel locks and a vise grip to get this one loose.  Be careful not to crank on or bend the metal line coming out of the fuel tank.  Its not hard to crease it and end up with a fuel leak here. After the line is disconnected, you have the choice of removing it or just pushing it off to the side and out of the way of the new line. From under the drivers side rear wheel well, locate the stock fuel line route and feed the 'A' line up and over the fuel tank.  Use teflon tape on the fitting and secure the 'A' line as pictured.
	14.  Route the new fuel line from the back of the car to the front. We recommend following the stock cluster of lines. Secure the SS with cushion clamps.  Use a 3/16" bit and drill into the sheet metal under the car to fasten the cushion clamps with sheet metal screws. Don't try to drill through the thick unibody frame members. Pay particular attention to following the contour of the wheel well as you don't want the line to snag as the rear wheel travels on the suspension. We usually use 5-6 clamps on the underside front to back. At the front of the car, feed the line up through the cross member still following the stock lines. Once the line is in the engine compartment you'll need to use zip ties to secure the line to the stock line. Or,  if you have the engine out of the car, just continue to use cushion clamps to secure the line to the firewall. VERY IMPORTANT: Make sure you've routed the line behind the steering linkage boot and secured it so that it won't rub on any of the moving parts of the steering system.
	15.  Now that the 'A' line is routed up to the filter bracket, you can mark it, tape it, cut it and attach the straight hose end fitting if you need to. Use the rubber spacer you cut earlier and install the K&N filter in the top part of the  bracket as shown. Attach the 'A' hose to the bottom of the filter then bolt the bracket back in place.
	16.  Secure the 'B' line to the fuel pressure sender adapter sub-assembly as shown in the schematic and  then attach that to the top of the fuel filter. (This photo doesn't show the FP sender, but you will want to orient the assembly so that the sender 'points' to the throttle body) 17.  Reversing the procedure used to remove it, install the fuel rail and it's associated pieces.  Don't forget to hook up the return line and the vacuum line to the FPR [voice of experience here]
	18.  Connect the 45° fitting to the rail as shown. Ensure that the connector points down so that it will impinge the least on the throttle body bracket.
	19.  Using a die grinder and a heavy duty carbide bit, machine away the indicated area on the throttle body bracket. The best way to do this is to hold the bracket in place on the car and see where it rubs the 45° fitting, then remove more material. Repeat the process until there is at least 1/8" clearance. Secure the machined bracket in place.
20. Install the throttle body elbow, upper IC pipe, battery box and battery. We highly recommend using either a TMO datalogger or connecting +12V to the FP connector (behind the battery on the firewall)  to actuate the fuel pump relay to check for fuel system leaks prior to attempting to start the vehicle. We have been very pleased with the results obtained with this modification to our cars.  In general, we have found that our EGTs are measurably lower and O2s a little higher which allows a greater tuning range.  For those interested, our entire fuel and control system consists of: Stock DSM fuel pump SteveTek High Flow Delivery System 660 ND injectors APEXi SAFC We find this combination to be very well integrated. Enjoy!

Copyright 2000, by SteveTek Inc. 
Please direct any and all correspondence regarding this document to engineering_staff@stevetek.com