How Tos / Tech

Jeep Tech: How to Replace Your Leaky Fuel Injectors

Worn injectors can cause performance to fall off so gradually you’ll not notice it. But new injectors are apparent immediately.

If you’re experiencing leaking fuel injectors, you might think new O-rings will correct your engine’s fuel delivery problems, but you’d probably be wrong. O-rings might do the job but usually they are only a temporary fix. If your fuel system is leaking all over the intake manifold through the injectors, you’ll need to replace the injectors. And if you can change the O-rings, you can change the injectors. But you’ll still need a good shop manual.

This is how we discovered our 1990 Cherokee’s injectors were bad; they were spraying more fuel on the engine than in the engine. It was at night and all we noticed was a very slight gas odor so we thought it was a minor leak back at the fuel tank. We parked the Cherokee and forgot about it until the next morning. While it was warming up we decided the check for fuel leaks. Beneath the engine it looked like the fuel pump was pumping gas directly on the ground with none getting to the cylinders! We killed the engine immediately! The new O-rings had quit working.

If you’re not comfortable working with the fuel system—and you need be extremely competent because of the gas’ volatility—find a good shop in your area with experienced and competent techs. If you are okay working on the system, first find a good shop manual for the year and model of your Jeep. Make sure the manual includes good instructions and photos on the fuel injector installation. For instance, we used a Haynes Repair Manual for the Jeep Wrangler, 1987 through 2008, which uses the same 4.0L straight six as the 1990 Cherokee Laredo (the vehicle we used for photography).

Author’s Note: Exchanging the injectors will be the same for all Jeep 4.0L engines, only the external accessories might be different and/or in different locations.

Although we found that the instructions in our Haynes Repair Manual were very complete and excellent, there were a few steps that we felt were unnecessary. Read through all the instructions a couple times before you begin the procedure, and try to identify each component as it’s mentioned. Do this a few times. Trust me; this will work in your favor later on when you’re deep into the task.

Summit Racing offers remanufactured Jeep fuel injectors and new units for the 4.0L straight six. Since the XJ is 25 years old—and we’re not trying to restore it back to showroom fresh, just able to run the trails and cruise the highways and byways—we chose the remanufactured injectors. Summit Racing also offers a full line of Haynes Repair Manuals.

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Once the fuel injectors were replaced, trail running in the XJ was fun again—and odor free.

Each individual injector is packaged separately from Summit Racing, in case only one or two are needed to correct the problem. We decided to replace all of them at one time.

To relieve fuel pressure, remove the gas cap. Disconnect the battery’s negative cable. Remove all the accessories from the top of the engine (air cleaner, etc.).

Tag each injector with its number and begin disconnecting vacuum lines and electrical connections.

You can see the injector is not seated fully.

After tagging them begin disconnecting the injectors

Use masking tape and/or indelible ink pen and identify every tube, line and wire before disconnecting them.

Loosen the bolts holding the fuel rail down.

One at a time, disconnect the control wires from the injectors.

Be careful, the older the connectors are, the more brittle them may become.

Notice the number on the injector’s connector.

You have to loosen the fuel lines.

Free up each injector.

Disconnect every line.

Continue to disconnect each piece.

Some components may not be readily seen at first, just carefully keep removing the parts.

A few items will have be removed because they are in the way, not because they are part of the fuel system.

Remove the entire fuel rail as one unit.

Carefully maneuver the frame rail around any obstacles.

Thoroughly clean each component that you’ve removed.

Disconnect the individual fuel injectors from the fuel rail.

Install the new injectors onto the fuel rail.

After cleaning everything thoroughly, carefully reinsert the fuel rail with the injectors onboard back into place.

Insert all six injectors into place and begin securing everything back into place.

Everything is back in place and ready for the air cleaner.

Worn injectors can cause performance to fall off so gradually you’ll not notice it. But new injectors are apparent immediately.

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