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Upgrading Jeep Cherokee XJ 4.0L Injectors

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.

Tools/Parts
- Flat head screwdriver
- Masking tape
- 6 new/rebuilt fuel injectors with new o-rings on each end
- Vaseline
- 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

Lets Begin
- Remove the fuel filler cap and disconnect the battery.

 

- 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.

 

7 thoughts on “Upgrading Jeep Cherokee XJ 4.0L Injectors

  1. This is Great, I would like to get something with a slightly higher flow rate like a 440cc injector, But then i would have to re-tune it.

  2. This also works with 97-06 Jeep Wranglers, but instead of rebuilt injectors I got mine from a local “you pull” junk yard. Make sure you get the ones with the right electrical connectors. 4 cylinder cars like 90s Neons and Breezes have the one your looking for.

  3. I grabbed the ones I used for the writeup from the junkyard also, then cleaned and rebuilt them. I strongly advise you either clean/rebuild them yourself if you’re going to do that, since most of the benefit of this swap comes from having nice clean, freshly rebuilt injectors instead of the old dirty ones. Swapping new dirty ones for the old dirty ones won’t get you much of a benefit, and may even hurt the performance.

  4. Excellent write-up! I’ve had the orange ford injectors (from a police interceptor) sitting around for a year! Finally installed them today. I followed each step, except I didn’t remove the breather tube- wasn’t in the way. The O-rings & disconnect tool cost me $21 at Advance Auto, injectors ran about $30 at the JY. The stock O-rings seemed a teensy bit thicker, but no fuel leaks, and the idle was purring delightfully on the first start. Just got back from a test drive and there’s definitely much better throttle response! Not that I needed more- I just like saying I have police interceptor injectors! Haha! Mine is a 97 XJ 4.0 with 249k miles and runs perfectly. Was averaging 14.67mpg- hopefully, this cheap & easy mod will put me around 16-17 mark!

  5. I recently had a 1997 Cherokee 4.0 overheat. ..cracked the head and the block. Replaced the engine with a 2001 4.0. However the mechanic used the fuel rail and new Bosch 4 hole injectors from the old engine on the replacement. The injector numbers for the 2001 engine are different, and I read the type “EV1″ from the old engine is different from “EV6/USCAR” recommended for the replacement. Would I be berrer off to demand the mechanic replace the original fuel rail and old original injectors on the replacement engine? (The fuel economy is terrible!!)

  6. I just read an article that was posted on morris 4×4, where they swapped out injectors from a doge neon and installed them in a Cherokee 4.0, they mentioned the 703 injector specifically – so my question is – what year neon injector will be compatible with my 99 Cherokee 4.0 ?

  7. Good write up. I have a 2000 Jeep Cherokee and narrowed down issues running to the fuel injectors. I liked the idea of the 4 port injectors so I went to the salvage yard and pulled some injectors from the Dodge neons like it says. When I got back home I was compairing the injectors and noticed the neon injectors are about 1/2″ shorter. My jeep injectors look identical to the pic above. The skinny black ones. I am open to suggestions on how to fix this.

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