Tech Tips: Fuel System Series

Lethal Performance Tech Tips | Fuel System Series


With any build, whether you’re gunning for 600rwhp or 1500rwhp, you’re gonna need fuel.


Here at Lethal Performance, we offer fuel system options for just about every level of horsepower, from the budget build to 2000rwhp builds. You can purchase the systems complete with everything needed to install, but it’s important to understand the components of the system for installation & purpose. That’s where our latest Tech Tips series comes in!


With each episode, Jared will go over the components that come in our fuel systems, from the budget kits which use the factory feed line & fuel rails to the complete systems that come with everything from rails to pumps. Be sure to bookmark this page, as we will add each episode below as they are released.


Episode 1: The Lethal Performance Return Style Harness



When converting your factory returnless setup to return style, wiring is key. Fortunately, we’ve made it easy! Our dual & triple return style harnesses are included in every Lethal Performance / divisionX fuel system but did you know they can also be used in just about any other return style setup? You can simply cut the fuel hat connector off of the end of the harness and splice the harness to your own fuel hat wiring. #nowyouknow


Our return style harness has multiple components: 

  • Fusible link
  • Relays
  • Ground wires
  • Trigger wire
  • Fuse holders
  • OEM style connector


Let's start with the included fusible link.



These are included with every harness. The link will connect to the positive terminal on your battery box. The 10g wires will then connect to the long 10g power wires of the harness that lead to the relays.



Each harness will include 2 or 3 relays, depending on which harness you order. These will control the pumps. The relays are powered via the fusible link and have attached black wires which are the grounds. You will need to ground these to an appropriate spot on the vehicle.



Also attached to the relays is a blue wire. This is the trigger wire that will tell the pumps to work. It can be wired in 2 different ways, either as a ‘key on’ setup or to prime like the factory pump(s).


After the relays you will find 2 (or 3) fuse holders wired in, each containing a 20amp fuse.



These fuses protect the relays if there is a short between the pumps and the relays. The fuses can also be upgraded to a larger amperage should you need it for larger pumps.


The last section of the harness is a loomed section coming from the fuse holders which leads down to the OEM style 6-pin connector. This connector will plug directly into the divisionX Gen 3 SN95 fuel hat OR you can cut the connector off and wire the harness directly to your own fuel hat setup. We will cover more of the connection options when we discuss the fuel hats in future episodes.

Episode 2: The divisionX SN95 Fuel Pump Hat



In episode 2 of our Fuel System Series, Jared goes over the basics of the divisionX fuel pump hat for the 99-04 Mustang.



We use these fuel pump hats in all of our Lethal Performance and divisionX fuel systems for the 99-04 GT, Mach 1 and Cobra models. We offer systems ranging from the Budget & Budget Plus kits to the full 1400+rwhp fuel systems. This hat is a direct replacement for your factory fuel hat setup, making it super easy to convert to a return style system and support tons of horsepower without worrying about sumps, external pumps, etc.


NOTE: This hat will work in the GT and Mach 1 factory tanks, however you will need to remove the plastic basket at the bottom of the tank that supported the factory fuel pump setup. Also to note, the 03-04 Cobra fuel tanks have a superior baffle system which helps to eliminate fuel starvation due to fuel slosh. If you have a GT or Mach 1 you can choose to upgrade to the Lethal Performance 03 Cobra style fuel tank (CLICK HERE).


Let’s break down the essential pieces to the hat:

  • OEM-style 6-pin connector
  • Feed & Return Ports
  • OEM Level Sender attachment
  • Fuel pump connectors & wiring
  • Fuel pump basket


The divisionX fuel hat has one prominent feature not found elsewhere: the OEM-style 6-pin connector on top. What’s the mean? Not only is it a leak-proof design, but it also gives you a plug & play wiring option using either our Lethal Performance Return Style Harness (discussed in Episode 1) or, if you want to use your own wiring, our 6-pin pigtail (SKU: DX-0045).

If you choose to use our Lethal harness (or if you purchase a complete fuel system that comes with the harness), the system will be plug & play. The harness plugs directly into the connector at the top of the hat. There will be 2 loose wires for the level sender that get wired to your factory harness.



To access the level sender wires in your factory harness, simply cut the connections and peel back the wire loom to reveal the OEM wires. There will be 4 wires, 2 small and 2 large. The 2 small wires will be your level sender wires. You will connect the yellow wire to yellow wire and black wire to black wire (however, these wires are run by ohms and not done by positive/negative so you could cross them and the sender will still work properly).

NOTE: Sometimes, the level sender will need to re-learn. If your fuel level is not reading properly, give the car some time/miles to adapt.


If you are using your own wiring, you can purchase the divisionX pigtail (CLICK HERE). This pigtail has the same connector as our Lethal harness to plug directly into the fuel hat, but allows you to wire in your own setup, including the same level sender wires.



The divisionX SN95 fuel hat will come with the feed & return fittings already installed. The feed fitting supplied is a 10an O-ring and the return port has an 8an O-ring. These fittings can easily be swapped out to accommodate different sized lines.


On the underside of the SN95 fuel hat, we’ll start with the spine of the hat. This is where you can attach your OEM level sender. The fuel hat accepts the 03-04 Cobra level sender with no bracket needed. If you have a 99-04 GT/Mach 1 or a 99-01 Cobra, you can purchase the divisionX level sender bracket (DX-37011) and use your OEM level sender.



There are also 2 wires on the underside of the hat for wiring up the level sender—one with a spade connector and one with a terminal. The terminal will be grounded to the spine of the fuel hat while the spade connector will connect to the spade connector on your factory level sender.



Also on the underside of the hat you will find the fuel pump connectors which allow plug & play use of most fuel pumps.


The bottommost part of the fuel hat is the fuel pump basket, equipped with o-rings for seating of the fuel pumps. The divisionX fuel pump hat accommodates the most popular fuel pump choices from both Walbro and Aeromotive.


Here are the pumps you can use in the SN95 fuel hat:

  • Walbro 255lph (SKU: WAL-GSS342)
  • Aeromotive Stealth 340lph (AER-11542)
  • Walbro 400lph (SKU: WAL-F90000267)
  • Walbro 465lph (SKU: WAL-F90000267)
  • Walbro 465lph High Pressure (SKU: WAL-F90000274)
  • Walbro 485lph (SKU: WAL-F90000285)


Check out the fuel chart below for their flow rates & E85 compatibility:



IMPORTANT: When installing the fuel pumps, you will want to make sure that they are positioned so that the bottom of the fuel filter sock is 1.75”-1.87” from the bottom of the fuel hat basket. This will insure that you have the proper placement for fuel pickup.



CLICK HERE for the full instructions on the divisionX SN95 fuel pump hat.


Stay tuned for Episode 3 next week covering the divisionX hat for the S197/Coyote platforms!


If you have any questions, please feel free to give us a shout. Stay tuned for future episodes of our Fuel System Series where we’ll go over more components of the return style fuel system.