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Premium Member
560 Posts
Discussion Starter · #1 · (Edited)
Greetings all!
In this write-up I will guide you on how to modify the Fuel Rail on your 4.7L engine. I will discuss two different ways to do this, one which is more cost effective and the other which better achieves the goals of this modification.
What are the goals of this modification you ask? They are twofold:

1. To decrease the amount of time fuel spends in the fuel rail. This lowers the total
temperature of fuel and reduces differences of temperatures between each injector.
2. Balance the flow and pressure of fuel among all the injectors.

This modification is based off the idea of another fellow who did this to his Dakota. You can find his write-up here and I credit him for coming up with this mod:

He did research on the temperature of fuel, how it affects the efficiency of the engine, and Duner's Fuel Rail cooling. He came to the conclusion that it's not entirely fuel temperature that affects the engine's efficiency therefore cooling the fuel may not be the answer. Instead the temperature of the fuel at each injector needs to be uniform to allow similar combustion efficiency in each cylinder. This should increase efficiency and take some work away from the computer as it doesn't have to try to achieve an optimal fuel/air ratio in cylinders that are all burning differently.

After completing this mod I have noticed that my throttle response is a lot quicker and my Jeep has more power as it keeps pulling hard through each gear. I am still evaluating any increase in MPG but so far it looks like 1-3 extra MPG.
I wonder if the last cylinder in bank 2 is so problem prone because it's the last cylinder in the fuel rail and therefore it burns the hottest.

The two ways to do this are:
1. With two fuel rails. The one on your engine now (or another) and another from a junk
yard or wherever. You need two passenger side rails (this side has a 4AN pressure
test port that will be used as the new fuel input).
2. Using your existing (or an extra) fuel rail only. Doesn't provide quite the cooling and
efficiency of distribution of fuel. I HIGHLY recommend buying an extra rail to do
this as you could leave your engine disabled if something goes wrong.

Tools Needed:
-8mm socket for the fuel rail bolts
-10mm socket for the spark plug coils and resonator box
-Shop towels for cleaning up spilt gas and cleaning components
-Flat Head Screwdriver OR socket for hose clamps
-Access to a Vise
-Hack saw (or Dremel) with a good blade for metal cutting
-Masking Tape for marking where to cut the fuel rail
-EFI Fuel Rail Disconnect Tool, or in my case, a strip of plastic cut off an empty milk jug :)
-Valve Stem Core Remover (only needed for Mod 1)

Parts needed for either mod:
-6AN Push-Loc Hose Barb to 6AN female 90° Elbow (JEGS #110071)
-6AN Push-Loc Hose Barb to 6AN female straight (JEGS #110051)
-6AN Male to 5/16 Male Push-on EFI (JEGS #640930)
-6 Fuel Injection Hose Clamps (JEGS #16047, 10-pack)
-200+ grit sand paper

Parts needed strictly for Modification 1: (Push-Loc = Push-On = Twist-Loc)
-Fuel Rail off a 4.7L engine in good shape. Can be taken off a Dodge or a Jeep, should
be identical but check to make sure. I got one from a salvage yard for $50
-1 foot of 6AN push-loc (or twist-loc) hose (make sure it's safe for gasoline) (6AN = 3/8)
-2 feet of 4AN push-loc (or twist-loc) hose (make sure it's safe for gasoline) (4AN = 1/4)
-2 3/8" x 1" barbed hose plugs for capping off the cut crossover ends
-6AN x 4AN x 4AN all male y fitting (Got off EBay for $15)
-Two 45° 4AN Push-On Hose Barb to 4AN Female fittings (SUMMIT #MRG-P454)
-Two 120° 4AN Push-On Hose Barb to 4AN Female Fittings (SUMMIT #MRG-P1204)

Parts needed strictly for Modification 2: (Push-Loc = Push-On = Twist-Loc)
-2 feet of 6AN push-loc hose (make sure it's safe for gasoline) (6AN = 3/8)
-6AN x 6AN x 6AN all male Y-fitting (Got off EBay for $18)
-EFI Fuel Rail Fitting - 6AN Male to 5/16" Hard Line (JEGS #103100)
-6AN Flare Cap (JEGS #110312)
-Two 45° 6AN Push-Loc Hose Barb to 6AN Female fittings (JEGS #110061)
Pictures of the parts are below (I got the Y-Fittings off of Ebay for about $15 each):

Parts from JEGS:

Parts from SUMMIT

Hose Plugs (Got off Ebay)

Fuel Rail:

Let's get to it!


-Remove the Fuel Pump Relay switch found in the fuse box under the hood. See Picture

-Start your engine, it will die after a few seconds. Then keep cranking until the engine no longer sputters. This releases the pressure in the Fuel System.
-Disconnect the negative terminal of your battery and isolate
-Remove your intake resonator and hose. Remove more if necessary to gain easy access to the fuel rail.
-Remove the 8 ignition coils from the engine. All the coils are the same so the order in which you reinstall them really doesn't matter. The nuts are 10mm in size. Keep in mind the location of the resistors and the grounding straps mounted on 4 of the coils. See picture below, there is a resistor and strap on either side of the engine.

-Disconnect all the injectors. You DON'T want to mix these up. However, the connectors are only given enough wire length to reach their respective injectors so mixing them up shouldn't happen easily. There are red clip locks on each connector that you need to slide toward the back of to connector. After you slide the lock back , you can press the tab and slide it off the injector. I broke almost every red clip lock trying to get them off because of how dried out and brittle they were. They are not required for the connector to stay on, they just prevent the tab from being pressed.

-There any many wires and hoses/tubes that run over the fuel rail to get to their destination. Push aside/tuck away all you can to clear the area for fuel rail removal. You DON'T want to man handle the fuel rail because you can cause damage to the injectors which will still be attached. One thing to keep in mind are the EVAP/Breather hoses coming
off the driver's side of the throttle body. They are hard plastic and after a while under the hood get VERY brittle. I broke one while just trying to get it off the throttle body.

-After clearing as much as possible around the Fuel Rail, turn your attention to the Fuel Rail connection. There is a silver safety lock that you must remove first. See Picture

-Now that the safety clip is removed you have to either use a tool designed to disconnect fuel rail fittings or a little trick I found. If you have the tool...GREAT! Slide the tool underneath the connector and you will be able to pull the connector off. If you don't have the special tool you can do what I did. Cut a strip of plastic out of a store bought milk
or water jug that's about 2" long and 1/2 inch thick. See Picture

-Take the strip, wrap it around the fuel inlet tube, and then push/slide it up into the connector. This will push the 4 clips inside the connector away from the tube and allow it to separate. You may have to wiggle it a bit to get it to disengage. See Picture

-Now that the Fuel Line is disconnected from the rail, it's time to remove the rail from the engine. Ensure that the areas around the injector holes are clean and free of any debris. You don't want dirt falling into the cylinders/intake valves. Remove the 4 8mm bolts holding the fuel rail to the engine. There are two bolts on either side. See Picture

With the bolts out, you can work around the rail slowly loosening and pulling the injectors out of their ports. BE GENTLE, the tip of the injectors are easily damaged. Pull the rail completely away from the engine. All 8 injectors will come with it. Now proceed to remove each injector from the fuel rail. There is a clip that holds them to the rail and in the right orientation. See Picture

Remove the clip by spreading it apart with your thumbs and pushing it toward the outside of the fuel rail. After the clip is off, the injector can be removed by pulling it away from the rail. The injectors for me took some good pulling/twisting to get them out.
This is a good time to replace any injectors that may be malfunctioning or damaged. Inspect for damage and replace if necessary.

---------Modify Fuel Rail -----------

Now it's time to modify the Fuel Rail. Proceed the following steps using either the one you got from the junk yard or the one you just removed (AT YOUR OWN RISK!). Keep in mind that if you are doing MOD1 you only need to do the below steps for the passenger side of the rail since it's the only side that will be used.

Take your Fuel Rail and using masking tape measure up the crossover 4" at either side, this is where you will cut the crossover and separate the two sides. See Pictures

Using your sandpaper, clean the cut ends of the existing crossover tube and remove any sharp edges. Be careful not to let any dirt/debris/sandpaper grit fall into either rail. Otherwise the injectors could pick it up and get clogged.

------------Build Main Fuel Feed-------------

Proceed to build the main feed out of these parts (More details on the parts in the first thread):
-6AN Hose to 6AN Female 90° Elbow
-6AN Hose to 6AN Female straight
-6AN Male to 5/16 Male Push-on EFI
-5.5" of 6AN Hose (Measure to ensure 5.5" is correct for your application)

Assemble the parts as seen below.

Using Push-Loc (Or Push-On, Twist-Loc) Hose with matching fittings can be pretty tricky. The barbs on the fittings are larger and sharper to grab the hose strong enough as to not need clamps. One trick that I've read about is coating the fitting and inside of hose with dish soap. Then using a vise to hold the fitting (NOT too tightly!! The fittings are aluminum and will crush easily in a vise!), grasp the hose and push it onto the bard end of the fitting until the hose pushes against the hose cap included on the fitting and doesn't turn freely. See Picture

Once the Main Feed is complete you can now move on to either constructing Mod 1 OR Mod 2 depending on what you want to do and what you can afford.

I will cover both in the next steps starting with MOD 1.

Premium Member
560 Posts
Discussion Starter · #2 · (Edited)
4.7L Fuel Rail Modification Continued...

-------------------- MOD 1 --------------------

Attach the 6AN x 4AN x 4AN Y-Fitting to the Main Feed and then attach the 4AN 45° elbows to create what's pictured below with the 45s pointing left and right. It's a bad quality photo, sorry bout that. Don't tighten them down too much, you will need to remove/adjust them later.

Take your two passenger side rails with the 4AN test ports.

Using a valve core remover, remove the core from each.

Now you want to cap each cut crossover piece on each rail. Using 6AN hose, EFI hose clamps, and the hose plugs cap each crossover elbow as seen below. Make sure the clamps are nice and tight. There are several ways this could be done. With hard line to AN adapters and then close the open end with a flare cap, weld the tubes shut...etc, the main goal is to seal off the ends so fuel doesn't pour everywhere....obviously. The method I chose seen below was inexpensive and got the job done.

After you cap the cut crossover ends you are ready to install Fuel Rail MOD 1 back onto your engine. I will discuss reinstallation after I cover MOD 2.

------------------- MOD 2 -------------------

Attach the 6AN x 6AN x 6AN Y-Fitting to the Main Feed and then attach the 6AN 45° elbows pointing down to create what's pictured below. Don't tighten them down too much, you will need to remove/adjust them later.

Cut two (2) 8" pieces of 6AN hose and attach to both 45° elbows. I had cut 7" which you will see in the picture below and was a little short. 8" should be just about right. Adjust accordingly for your application.

Then take the other ends of the hoses and slide them over the sanded/cleaned crossover pipe on either side of the Rail. Hold the hoses in place with three (3) EFI hose clamps on either side
Using the EFI Fuel Rail Fitting (6AN Male to 5/16" Hard Line) and 6AN Flare Cap, cap the old fuel inlet on the driver side of the fuel rail. See Picture

You will now have the complete assembly for MOD 2.


All that's needed now is to reinstall the fuel rail (MOD 1 or MOD 2). For MOD 2 you will probably want to take the hoses off the cut crossover ends for easier installation of each rail.

Push the top of each injector back into their ports on the rail and secure with the clip. They may be tricky because the O-Rings on the injectors is pretty thick and may bind. I used a very small amount of new engine oil to moisten the o-rings and inside wall of each port to assist with reassembly.

After each injector is back in place on each rail carefully reposition the rails and the injectors with their ports on the top of the engine. AGAIN, you don't want to damage the end of the injectors! Carefully work each injector back into their ports and then secure each rail with the two 8mm bolts.

The Driver side rail for MOD 1 requires that you run the cut and capped crossover elbow around the fuel line coming up from behind the engine. See Picture

After the rails are mounted, proceed on reinstalling all your coils, resistors, ground straps, and plugging in anything that was disconnected (injectors, coils, possibly more).

Take the Main Feed (with either the setup for MOD 1 or MOD 2) and push the EFI adapter into the fuel line connector. It will lock into place when you get it all the way in. Replace the safety clip. Find a good placement for the Main Feed where the hose is not kinked and you are not twisting the stock fuel line too much. You also want the Y-Fitting in the middle of the intake manifold.

I found that running the Main Feed as seen below was suitable and held it in place

----------Install MOD 1-----------

Cut two (2) 9" lengths of 4AN hose. Take a measurement to make sure though because your application may require a different length. The hose must run from the 45 elbows on the Y-Fitting to the 120 elbows on the test ports. DON'T forget to include the length needed to slide the hose onto each fitting. Each fitting will need about 1". Push the 120° 4AN elbows on to one side of each hose and the 45° 4AN elbows to the other side of each hose. You will end up with two hose assemblies with a 120°and a 45° on each. Attach the 120s to the test ports (the new fuel inlets) and the 45s to the Y-Fitting. Don't tighten them down yet, just finger tight. You will need to adjust them. Here are the 120s on the test ports without hose.

----------Install MOD 2-----------

Reattach the 6AN hoses to each crossover end using the EFI hose clamps to secure them in place.

-----------FINAL STEPS------------

After getting all the hoses and fittings hooked up, start tightening all the fittings making sure that they are not twisting or kinking hose.

DO NOT OVERTIGHTEN THE FITTINGS! They are only aluminum and the seal created by AN fittings doesn't need them to be super tight. DON'T use any kind of sealant or tape on the threads. AN fittings are designed to create a tight seal without any of that. Tighten them until they are really snug using a short crescent wrench

MOD1 Installed:

MOD2 Installed:

Reinstall your fuel jump relay and start your engine. Give the engine a good few revs and hold the RPMs at about 2,000 or so to clear out any air. Check for any leaks while you do this. If you spot any shut of the engine immediately and do what needs to be done to fix it.

Reinstall your resonator box and tube and anything else that you may have removed during this process.
Go for a test drive and test out your new mod!

Thanks for reading! I'd love to hear about your experience with this modification and what it did for your performance and efficiency. If you need any tips/help/advice please feel free to post it here or send me a PM.

-Jeep Boy
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Premium Member
560 Posts
Discussion Starter · #3 · (Edited)
*******UPDATE 12/17/2013
The hose clamps on the passenger side rail came loose on me and the rail cap came off while the engine was running. This was neglect on my part as I didn't check the tightness of the clamps for a few months. Needless to say...fuel sprayed everywhere and I had to let it evaporate for a while...

To fix this issue for good I purchased 2 -6AN to 3/8 Hard-Line fittings and caps.

Flare Cap:

Cost me right around $30 for 2 of each. They didn't need much tightening to really grab on to the fuel rail. I tried pulling them off and they are not going anywhere.

Driver Side Rail:

Passenger Side Rail:

These fittings can be used with either Mod. They are just end caps/pressure test ports for Mod 1 but for Mod 2 you will need to change things up a bit. You will need to buy 2 more - 45 Degree 6AN to 6AN Push-Loc Hose fittings at $9.99 each from JEGS #110061. These will be installed at the end of the compression fittings and then hose will need to be cut to fit between the 45s on the Y-Fitting and new ones you just installed. A much stronger way to grab onto the fuel rail then rubber hose and clamps.

YETI - The Abominable WJ
3,762 Posts
It is a really cool mod, but I don't know that I would do it as it is pretty involved. I would likely get some type of wrap for the fuel rail before I disassembled this much. Or maybe if I had to do injectors, I would do it at that time.

Premium Member
560 Posts
Discussion Starter · #5 ·
It is a really cool mod, but I don't know that I would do it as it is pretty involved. I would likely get some type of wrap for the fuel rail before I disassembled this much. Or maybe if I had to do injectors, I would do it at that time.
Hey thanks IrocZ! It was definitely an interesting mod to try!
It's actually not too bad, it looks bad but it doesn't take much to remove the entire fuel rail. And once you have it in two pieces, its much easier to install. The injectors also come out and go back in pretty easily, i was actually surprised.

Wrap would be the quickest and most inexpensive way to keep heat away from the rail. I've read about several folks who used the wrap and had good results.

40 Posts
so after all said and done how much did you spend on this mod?

Premium Member
560 Posts
Discussion Starter · #7 ·
so after all said and done how much did you spend on this mod?
Total cost to install Mod 1 was about $165

Total cost to install Mod 2 was about $110

Roughly $250 for all the parts to try both modifications.

I recently made an update to both Mods as the hose clamp rail caps didn't hold up and one ended up coming off while the engine was running. The update entails removing the hose rail caps and replacing them with compression fittings that will stay put. The Compression fittings cost $30 for two fittings and two caps (see above for more info) BUT:

--Using the compression fittings for Mod 1 saves you around $12
(no hose plugs and clamps needed)

--Using the compression fittings for Mod 2 saves you $6.99 for the clamps, however, you will need to buy 2 more - 45 Degree 6AN to 6AN Push-Loc Hose fittings at $9.99 each from JEGS #110061. These will be installed at the end of the compression fittings and then hose will need to be cut to fit between the 45s on the Y-Fitting and new ones you just installed.

2 Posts
Custon fuel rail.;

Hey there Jeep Boy and everyone.

Great post about the fuel rail mod.

Have a question. Since there is no fuel rail return line on the WJ 4.7.

Waht do u think about that fuel rail. Take 2 bare fuel rail and mod to bcame 4 seprate fuel rails 2 injectors each.

The reason is that i read WJ have 2 problems heat and the time that the fuel spend in the system.

Tell me what u think.

Tks a lot.



Need some opinions about this project.

tks again

Premium Member
560 Posts
Discussion Starter · #9 ·
Interesting concept pasair777!
That would pretty much reduce the temperature as far as possible without wrapping the rail with insulation and/or installing a return line system.

It is definitely a tougher design to build as you have to close off the open end of the rail after you cut it and you also have to attach (through welding more then likely) an AN fitting to each cut piece. Would also be more expensive since you would need more fittings. If you go through with this project, be sure to post some pictures so we can see the end result!

2 Posts
Tks jeep boy.

No doubt it is a little more expensive and laborious project.

But what the hell, we have to feed our children right? hehe

The idea is more cold fuel, equal distribution, I read somewhere about problems because of fuel stravation in some cylinders..

AND the MOST importante, easy acess to removel the lines and injectors. Man waht a PITA to remove the stock fuel rail. Im trying to take the intake manifold out and man...

Seriously, I thought about cutting out everything.

Surely I will send photos if I go ahead with this idea.


00 GC 4.7

2 Posts
It's good to see my idea take root here. It's been almost 6 years since I modified my Dakota's fuel rail in this manner, and I have never had any problems running the engine with this modification. I did have a few times where a little fuel would leak, when I applied a little side pressure to each fuel hose going to either rail, but nothing else springs to mind.

I am going to do this modification to my 2001 Durango. I am currently in the process of swapping in a 2009 Corsair 4.7L engine, to replace the original engine that lost a conrod bearing for cylinder 8. I have already swapped tone rings, and the new engine is in - I just need to finish bolting it in, then install various and sundry engine accessories.

Premium Member
560 Posts
Discussion Starter · #12 ·
t vago,
Thanks for the comment! You still seeing good results from this mod on your Dakota?


2 Posts
Yes, I am still seeing good results. Mainly, I see improved response if my truck has been heat-soaked (such as running on the highway for a while, stopping for ~10 minutes, then going back on the highway). Fuel economy has also improved a bit.

I do see something that seems a bit odd, if the truck has been sitting overnight in cold weather. Mainly, the engine will sputter for a few seconds, almost like the fuel pump isn't delivering fuel. After that, the truck will run normally.

1 Posts
Yes, I am still seeing good results. Mainly, I see improved response if my truck has been heat-soaked (such as running on the highway for a while, stopping for ~10 minutes, then going back on the highway). Fuel economy has also improved a bit.

I do see something that seems a bit odd, if the truck has been sitting overnight in cold weather. Mainly, the engine will sputter for a few seconds, almost like the fuel pump isn't delivering fuel. After that, the truck will run normally.
Thanks to the both of you,great ideas. I'm putting together a 2000 sport with an 2002 HO Motor and my thought is the temperature/pressure difference is greatest in the 6-8 cylinder fuel rail area so to me tapping into the center of the rail is best.I only added drilling the shrader fittings to remove internal threads and resize the hole in the rail.j


1 Posts
I just wanted to thank you for posting this information and the others for sharing their ideas. I have only owned my 2004 Jeep Grand Cherokee 4.7L HO Overland for a couple of years. This is my first Jeep, and I did not what I was getting myself into and didn't know how much work this used vehicle needed until I discovered the previous owner(s) didn't do much maintenance. It had about 185k miles on it when I bought it and the oil was the only fluid they changed. The body looked clean and the engine sounded smooth (other than the exhaust leak). It even had the original 2003 Chrysler transmission filter. Found out about death wobble the hard way, but the front end is nice and tight now after replacing everything that was worn out. I feel like I've spent more time under the Jeep and repairing it than actually driving it. lol

I've been banging my head like many others trying to find out how to fix the heat soak issue. Trying to research if it's the fuel rails, the injectors, the starter, or something else. I replaced my fuel injectors, added thermal insulation to the rails (and wrapped part of the downpipe from the exhaust manifold to the pre-cat since it runs right next to the starter) but forgot to add something around the actual injectors in case the fuel is boiling in them and leaking into the cylinders. And I too have burned up a starter trying to force it to overpower what seems like an excessive amount of compression in the cylinders when trying to restart the hot engine after only being shut off for 10-30 minutes.

I was going back and forth on which mod I was going to try and even went to Pick-n-Pull and pulled a spare fuel rail. I ordered enough parts to do either mod but ultimately went with a variation of Mod 1. Instead of capping the drivers side fuel rail quick connect, I used that for the fuel feed from the Y adapter instead of using a passenger side rail reversed for the drivers side.

I also decided not to cut and cap the connecting tube between the two rails. I don't know if this will have a negative impact (i.e., if there isn't enough pressure imbalance between the two rails to cause some flow between the connecting tube to keep the fuel in the connecting tube from sitting in there too long).

The reason I chose this adaptation of Mod 1 was to avoid removing the fuel rail and to avoid cutting/altering the stock rail (other then removing the valve stem for the passenger fuel pressure check port). I liked the idea of feeding the fuel midway into each rail but was tempted to go with with Mod 2 if I was going to cut the connecting tube anyway.

I also used 6AN connectors for everything and used a 4AN to 6AN expander on the passenger fuel pressure check port.

I can add the details of my procedure and parts used if anyone is interested.

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