XJ 4.0L Fuel Injector Swap

One of the easiest modifications on our beloved 4.0’s is a fuel injector swap. For some, this may sound like a technical and daunting task, but rest assured, it’s actually quite simple. The reason for this swap is simple. Jeep used 1-hole pintles on their injectors while Chrysler used 4-hole pintles on the rest of their products. The 4-hole pintle allows for a more even fuel spray pattern, resulting in better atomization, making the engine work less and run a little smoother.  The results you gain from this are a smoother idle and better throttle response. Some have seen a very mild gas-mileage gain, but this is due to running clean injectors as compared to the stock ones that are dirty.

87-98 XJ’s use what is commonly referred to as EV1 injectors. This is due to the electrical connection they have. The injector you need is Bosch part # 0280155703. These injectors can easily be found in most 95-97 Dodge/Plymouth Neon, Dodge Stratus, Plymouth Breeze, and Chrysler Cirrus vehicles with the 2.0 engine. Just be sure to check the side of the injector for the correct part number as Chrysler used many different injectors in the mid-90’s and early -00’s. One possiblity for the 87-98 XJ’s though is to use EV1-to-EV6 adapters. These will allow the use of EV6 njectors, making the hunt for the much harder to find 703’s a thing of the past.

99-01 XJ’s received an updated injector, called EV6 injectors. The injector you need is Bosch part # 0280155784. These can be found in most 98-01 Dodge Caravans, Plymouth Voyager, Dodge/Plymouth Neon, Dodge Stratus, Plymouth Breeze vehicles with the 2.4 engine. Again, be sure to check the side of the injector for the correct part number as Chrysler used many different injectors in the mid-90’s and early -00’s.

This image shows the difference between an Ev1 injector (on the right) and an EV6 injector (left)

ev6 ev1

When you’re looking for the correct injectors, just look on the side for the part #. Here is a 784 as an example:

injector

Some people have used 0280155710 injectors from Ford 302 V-8’s, but these have a lower flow rating and do not utilize retaining clips, so some slight modification is needed. With this in mind, I have found 703/784 injectors to work best with the Jeep 4.0. This swap can also be done to any ZJ or WJ that has the 4.0L.

Once you have 6 injectors, clean them up (a simple Google search will give more detail) and make sure to have new o-rings and micron filters. So, let’s get into the step-by-step.

Tools/supplies you’ll need:

- A medium sized flat blade screwdriver
– Masking tape / Painters tape
– 6 new/rebuilt fuel injectors with new o-rings on each end
– petroleum jelly (Vaseline)
– a 10mm deep socket w/ ratchet and extension
– fuel line quick disconnect tool (for 1996 and up engines IIRC)
– a few rags
– 1 hour of time (+/-)

The Process:

1. Unscrew the gas cap.

2. Disconnect the negative (black) terminal from the battery and place a rag on the battery to keep the terminal from touching the post.

battery

3. Remove the air intake tube from the throttle body and stuff a rag in the throttle body to keep crud out. Also disconnect the breather tube from the intake box.

4. Disconnect the throttle and cruise control (if equipped) cables from the throttle body.

5. Unscrew the test port cap on the fuel rail. You’ll want a rag below it as some fuel will spill out.

fuel rail pressure

6. Connected to each injector is a electrical wire. Use the masking tape to label these #1-6 from front to back. You do not want to mix these up when you reconnect them.

7. Disconnect the Fuel Pressure Regulator vacuum line from the intake manifold.

vacuum line

8. Disconnect the fuel lines from the fuel rail. This one is optional, but I recommend it as the lines aren’t very flexible. Up through ’95, just push in the white tabs and carefully pull. ’96+, you’ll need a disconnect tool (cheap at your local parts store).

fuel lines

9. Disconnect the electrical plugs from the injectors. For 87-98 XJ’s, just wiggle and pull. For 99-01’s.use the screwdriver to pop the red lock tab up and then pull the connector off the injector.

This is pretty much what you should be seeing at this point:

engine

10. Remove the 2 bolts holding the fuel rail on. Gently pull the fuel rail away from the engine.

11. Once the fuel rail is off, remove the small metal clips from the injectors. They are right where the injectors meet with the rail. You need to reuse these so don’t lose/bend/break them. The flat head screw driver works very well to pop them off.

12. Hold the rail vertically over something to catch some fuel (a medium tupperware container works very well, especially the kind Hillshire Farms lunch meat comes in) and remove the bottom injector. Some fuel should come out of the opening. then remove the injector from the opposite end. More fuel will come out. Now remove the other 4 injectors.

rail

13. Make sure that all the o-rings from the stock injectors are out of the rail and the engine. If there’s any gunk buildup in the engine holes, use the screw driver to clean the holes. Scrape the gunk off in an “inside to outside edge” pattern, being very careful to not let any crud get into the engine as this would be very bad. Clean the screwdriver off after each scrape.

port

14. Make sure the new injectors have the new  o-rings and pintle caps on them. Lube all the o-rings with a small amount of vaseline. This will keep them from tearing.

lube

15. Plug each injector into the rail, and refasten the metal clips to “lock” them in place.

16. Firmly press the rail and injectors into place on the engine and re-install the 2 fuel rail bolts.

17. Put a small amount of di-electric grease in each electrical plug and reconnect them to the injectors, following the # sequence you taped to the wires.

18. Reconnect everything – fuel lines, vacuum line, air intake, throttle/cruise cables, and battery terminal.

19. Check the ground. Anything there? No? Good. Recheck everything you disconnected. Is all connected again? Yes? Good.

20. Turn you ignition to “RUN”. DO NOT START THE ENGINE! Check around the injectors/fuel lines for any leaks. If there are none, go to the next step. If there is one, recheck the o-rings on the injectors. if there’s a tear in one it’ll leak.

21. Turn the ignition off, then back to “RUN” for a couple seconds. Now start it up. It may take a couple seconds. If the idle is choppy, wait a few minutes and it should smooth out. If it doesn’t and it’s not running smooth, follow next steps to reset your PCM into a “learning mode”.

Resetting the PCM:

This very simple procedure will Erase the “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed.

After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

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. You will run a little rich until the PCM adjusts for the new air/fuel mix.

**Full credit goes to Justin Raducha for the images used in the write up section of this post**

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8 thoughts on “XJ 4.0L Fuel Injector Swap

  1. Nice write up guys!
    When you un-hooked the negative terminal off the battery you reset the adaptive memory in the PCM on both Renix and JTEC so you don’t have to do the key cycle trick. Also be careful using the petroleum jelly to lubricate seal as sometime it can cause the rubber to swell, Try a dry silicone spray instead.

    • Thanks for the tips. The o-rings for the injectors are made from a different rubber though, designed to not swell due to oils and fuels, so no harm there. A dry silicone is never a bad choice though.

  2. The article says to make sure that the pintle caps are on the injectors but if im not mistaken the stock XJ injectors do not have the pintle caps Are they supposed to have them?

    • With the new injectors, yes, they are needed. The head design is different and the pintle cap keeps the injector centered in the port.

  3. Hey I went and picked up six injectors from an 01 pt cruiser 2.4 and they are to short. Are all of these to short?

    • You probably got a set of 740’s which are too short for use in the XJ. Check your injector part number (refer to the first few paragraphs of the article to see where the part number is located) and make sure you have the proper injectors (703’s for 88-98 XJ’s, 784’s for 99-01 XJ’s).

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