Swapping an LS engine into a 1984 Jeep is a dream for many off-road fans. But if you want your swap to run smoothly, you must build a fuel system that can handle the LS’s demands. This guide will walk you step by step through the 84 key parts and steps you need to get the job done right, even if you’re new to engine swaps.
Understanding The Ls Swap Fuel System
The LS engine needs high-pressure fuel injection, unlike the Jeep’s original carbureted setup. This means nearly every part of your old fuel system needs to change. You’ll need new lines, pumps, fittings, and safety upgrades. Missing even a small part can cause headaches or even engine failure.
84 Essential Items For An Ls Swap Fuel System On An 84 Jeep
- LS-compatible fuel tank
- High-pressure in-tank fuel pump
- Fuel pump wiring harness
- Fuel pump relay
- 10-gauge power wire
- 30-amp fuse
- Ground strap for pump
- Bulkhead fuel pump connector
- Fuel tank sending unit (LS pressure rated)
- Fuel return line port in tank
- Fuel vapor/vent line port
- Fuel filler neck (compatible with new tank)
- Fuel tank straps
- Fuel tank skid plate
- High-pressure fuel line (3/8” or 8AN)
- Fuel line fittings (AN or EFI rated)
- Fuel line clamps
- Rubber grommets for lines
- Proper line routing clips
- Fuel line heat shield
- Inline fuel filter (5-micron recommended)
- Spare fuel filter
- Fuel filter mounting bracket
- Fuel filter fittings (AN or metric)
- Inline fuel pressure regulator (58 psi fixed or adjustable)
- Fuel pressure gauge
- Fuel pressure sensor (for EFI monitoring)
- Return line (5/16” or 6AN)
- Return line fittings
- Return line clamps
- Return line heat shield
- Flexible EFI hose (for engine bay to hard line)
- Hard line (steel or aluminum)
- Pipe bender tool
- Fuel line flare tool
- Quick disconnect LS fuel rail fittings
- LS fuel rail
- LS fuel injector O-rings
- Fuel injector retaining clips
- Injector wiring harness
- Injector connector adapters (if needed)
- Intake manifold gaskets
- Intake manifold bolts
- Throttle body gasket
- Throttle body bolts
- LS compatible throttle body
- Throttle cable or drive-by-wire setup
- Accelerator pedal bracket
- Fuel pressure pulse damper
- Fuel rail mounting bolts
- Sealing washers for all fittings
- PTFE tape for threads
- Vapor canister (EVAP system)
- EVAP line (if using emissions controls)
- Vapor canister purge valve
- EVAP purge solenoid wiring
- Fuel tank rollover valve
- Fuel tank vent hose
- Hose clamps for vent
- Fuel cap (pressure rated)
- Fuel pump strainer
- Fuel pump insulator sleeve
- Fuel pump ground wire
- Fuel pump noise isolator
- Fuel line disconnect tool
- Hose cutter
- Fuel-safe zip ties
- Fire sleeve for lines near exhaust
- Heat shield tape
- Mounting hardware for regulator
- Rubber mounting washers
- Vibration isolators for fuel pump
- Wiring loom for fuel wiring
- Fuse holder for pump
- Weatherproof connectors
- Fuel leak test kit
- Thread sealant for fuel fittings
- Fuel line cleaning brush
- Service manual for LS wiring
- Wiring diagram (Jeep to LS ECU)
- LS ECU (proper tune for fuel system)
- OBD-II diagnostic scanner
- Fire extinguisher (for first startup)
- Safety glasses and gloves
Step-by-step Ls Swap Fuel System Installation
- Remove the old tank and lines. Clean under the Jeep.
- Install the new fuel tank. Check for leaks.
- Mount the high-pressure pump. Use vibration isolators.
- Wire the pump with a relay and fuse. Run 10-gauge wire for enough power.
- Run new fuel lines from the tank to the engine, avoiding sharp bends and heat sources.
- Install the inline filter as close to the engine as possible.
- Connect the return line from the regulator back to the tank.
- Mount the pressure regulator and set it to 58 psi.
- Attach quick disconnects for the LS fuel rail.
- Connect all wiring and test for leaks using your leak test kit.
- Prime the pump and check pressure before first startup.
- Double-check all fittings and clamps before driving.
Common Mistakes To Avoid
- Using rubber fuel hose instead of EFI-rated hose
- Skipping the return line (needed for proper pressure control)
- Running lines near the exhaust without heat shielding
- Forgetting a relay for the fuel pump
- Not using a 5-micron filter (can harm injectors)
Many beginners miss the importance of vibration isolators for the pump, which reduce noise and extend pump life. Another overlooked detail is the fuel tank vent system—without it, you’ll get vacuum lock and poor performance.
Example Data: Fuel Line Materials
Here’s a quick look at common fuel line options.
| Material | Pressure Rating | Pros | Cons |
|---|---|---|---|
| Rubber (Carbureted) | 30 psi | Cheap, easy to find | Not safe for EFI |
| EFI-rated Rubber | 100 psi | Flexible, safe for LS | Needs proper clamps |
| Steel Hard Line | 200+ psi | Durable, OEM style | Harder to bend |
| PTFE Hose (Braided) | 1000+ psi | Resistant to all fuels | Expensive |
Fuel Pump Options Compared
Choosing the right pump is critical for the LS swap. Let’s compare popular types:
| Pump Type | Flow Rate (lph) | Noise | Reliability |
|---|---|---|---|
| Walbro 255LPH In-Tank | 255 | Low | High |
| OEM GM LS Pump | 190 | Very Low | Very High |
| External Inline | 255+ | Moderate | Medium |
Final Thoughts
Upgrading the fuel system for an LS swap on an 84 Jeep is not just about buying a few parts. You need to carefully plan every step and make sure each item is high-quality and compatible. Taking shortcuts can lead to breakdowns or even dangerous leaks. If you’re unsure about wiring or pressure settings, consult a professional or use trusted resources like Holley’s fuel system guide.
Take your time, check each step, and your LS swap will reward you with power and reliability for years.
Frequently Asked Questions
How Much Pressure Does An Ls Fuel System Need?
Most LS engines require 58 psi of steady fuel pressure. Too low or too high can cause poor running or damage.
Can I Use My Jeep’s Stock Fuel Lines?
No, the original lines aren’t rated for EFI pressure. Use EFI-rated lines or steel hard line for safety.
What Size Fuel Pump Do I Need For A Stock Ls?
A 190–255 lph pump is enough for most stock or mild LS engines.
Do I Need A Return-style System?
Yes, most LS swaps work best with a return-style fuel system for stable pressure and temperature.
Is A Fuel Pressure Regulator Required?
Absolutely. The LS needs a regulator set to 58 psi. Some pumps have built-in regulators, but external is preferred for swaps.
