A popular modification for the older 4.0L Jeep Cherokee engines is to replace the stock fuel injectors. Stock injector have a single port, some aftermarket injectors have 4 ports (producing better throttle response, smoother idling, and MPG/power gains). Usually these types of injectors can be found in an early 90s Dodge Neon’s (as well as other vehicles). The model injector number you need depends on what year Cherokee you have.
- Flat head screwdriver
- Masking tape
- 6 new/rebuilt fuel injectors with new o-rings on each end
- A 10mm deep socket with ratchet and extension
- Fuel line quick disconnect tool (for 1996 and up engines IIRC)
- Eye protection
- A couple of rags
- Remove the cap on the fuel rail test port. Place a rag under the port and using a flat screwdriver, release the pressure inside the rail by pressing the Schroeder valve in. (Wear Eye Protection)
- Using the masking tape, label the wires running to each injector 1-2-3-4-5-6 from front to back. It’s very important to not mix these up. If the order is not correct you will have a misfire. Disconnect the injector electrical connectors after doing so. (1999 and down you just have to wiggle and pull. 2000/2001 have locking clips that you need to disengage to pull the connector off.)
- Disconnect the vacuum line from the fuel pressure regulator. You can remove the line at the manifold or at the regulator. Be careful it may be brittle. If you crack or break this line you will have a rough idle, due to a vacuum leak.
- Time to disconnect the fuel lines. This is optional, but a VERY good idea since the fuel hoses are not very flexible and the lines break easily. For pre-1996 engines, all you do is squeeze the white tabs together and CAREFULLY pull off the fuel line fitting. For 1996 and up engines, you will need a fuel line disconnect tool to separate the fittings. The fittings are different sizes so they can only go back on one way – no need to label them.
- Removing the air intake tube from the throttle body will make the removal of the fuel rail easier. Also stuff a rag in the throttle body to keep crud out. Removing the throttle cable and cruise control linage (Automatic Transmissions Only) isn’t a bad idea either. Remove the bolts holding the fuel rail to the intake manifold (10mm). The rear most bolt is a stud (10mm).
- Remove the fuel rail and injectors. Wiggling the rail back and forth while pulling with a little force should do the trick. Be careful not to bend the rail while doing this. Best to grab the rail at each end, using both hands. After removal, check the openings to make sure all the o-rings are out. Make sure nothing falls into these hole openings. To remove dirt and crud, scrape inside – out carefully with a flat head screw driver.
- Remove the old injectors from the fuel rail. There are metal “clip-nuts” that slide off the injector body where they attach to the rail. Use the flat blade screwdriver to pry them off. Make sure your new injectors came with new clip nuts before throwing these away, otherwise you will reuse them. Pull out each injector.
- Time for new injectors! The ones we installed are a rebuilt Neon “703″ injectors. They have about the same flow rate as the stock injectors, but instead of the one outlet hole, they have 4. This gives a better spray rather than a stream of fuel for a better atomization and burn (smoother idle and efficiency).
- Use the Vaseline to lightly lube up the injector o-rings. Push each fuel injector into the rail, making sure they are straight. After they are all seated, make sure they are rotated the correct way and install the clips.
- Reinstall injectors and fuel rail, making sure each injector is fully seated within the holes, and bolt the rail back up. The torque spec for the bolts is 20ft-lb. Reconnect the wiring connectors to the correct injectors. Reinstall the fuel lines making sure the clips re-lock when you press them on. Reinstall the vacuum line to the fuel pressure regulator. Bolt the throttle cable bracket back up, and reattach the cables to the throttle linkage. Reinstall the air intake tube to the throttle body (make sure to remove the rag). Screw the cap back onto the fuel rail testing port, put your gas cap back on, and reattach the battery.
- Turn the key to “ON” (do not start the engine). Go back to the engine bay and inspect for leaks around the injectors and the fuel lines. If no leaks, turn the key off and then turn it back to “ON” (do not start the engine) for a few seconds to prime the fuel lines. Then start the engine. It may take a few seconds to get the fuel to the engine. The idle may be choppy for a few minutes but should smooth out as everything adjusts.
Note: If you experience running issues with the injectors, or very poor gas mileage, you may need to reset the PCM back to factory air/fuel trims. To do this, follow this procedure:
-Disconnect the battery terminals and touch them together for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.)
Reconnect the Battery Cables
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”
The PCM Adaptive memory has now been flashed, or erased from the PCM.
When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.
When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.
The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
Special Thanks To Justin Raducha For Performing This Upgrade And For Supplying Us With Pictures.