Have you smelled fuel vapors coming through the heater vent on cold mornings? Maybe just caught a whiff of gasoline vapor when you open the hood? It is always a cause for concern and sometimes difficult to find the source since fuel quickly evaporates. I experienced this phenomenon on my 1988 Cherokee at 100K miles and again at 165K miles. In each case, I found the culprit to be one or more leaky fuel injector o-rings.

Troubleshooting

You're going to have to open the hood for this one. I know we don't like to do that as it usually cost money and some significant others actually forbid us from this risky operation, but I tell you it is the only way. With the engine running, look along the fuel injector rail (left side of engine from the driver's perspective). On older models like my 88, the injector rail is silver with a small silver canister (fuel pressure regulator) on the front side and six injectors pointing into the engine. Look for fuel leaking from anywhere along this rail. You may see fuel on the manifold heat shield directly below the injectors. In one case, mine was obvious as fuel was spraying out of the front two injectors. In another case, it was not obvious until I moved the injectors slightly that I saw the leak. Once you determine where a fuel leak is coming from turn off the motor.

What You'll Need

You will need a nearby dealership and a checkbook, or a few tools, $20 in parts, and a couple hours. The parts you will need are one o-ring repair kit and two quick connect line repair kits (although I would recommend buying at least three quick repair kits and a fourth wouldn't hurt). The o-ring kit contains six brown o-rings and seven black o-rings. The brown o-rings go on the engine side of the injector and six of the black o-rings go on the rail side of the injectors. The seventh black o-ring is to seal the fuel pressure regulator to the injector rail. The quick connect hose repair kits will be used on the inlet and outlet fuel line connections. They contain a plastic clip connector, two small orange o-rings and a spacer. I have gotten away with using the existing quick connectors, but for the few dollars and the ease of replacement why risk a leak. A minimum of two are required, but you may find another leak some where and an extra in the toolbox might be prized on day on the trail. As for tools, you need a 13mm socket with a short extension, small torx driver, small pair of pliers, and a small pick set is handy. While your gathering everything up, grab a couple shop towels/rags, some lubricant about the consistency of KY Jelly (Permatex Trans-Gel is preferred), and six sticky labels numbered 1-6.

Stepping You Through It

1) First, we must think safety. Take a second to disconnect the negative battery cable. Next remove the fuel cap to help depressurize the fuel system. Let the engine cool before performing any work. Also, DON'T damage the injector rail in any way. They are not repairable. It you find it damaged, do not try and repair it. Several Cherokees have burned violently due to fuel leaks along the injector rail assembly.

2) Next, place a rag under the pressure test port on the forward portion of the fuel rail. It's that little silver cap thing just aft of the fuel pressure regulator. Now, take the cap off. Don't worry, there is a valve under the cap like the ones on your tire. Take a small object and press the valve post in to relieve the pressure. A little gas may come out with a hiss. Dispose of soiled rag properly.

3) Before we get too far along, lets go ahead and label the wires going to each injector with the sticky labels. Just label them so you know which wire goes to which injector. It is just as important as keeping up with what plug wires go where when fooling around on the other side of the motor.

4) Look at the rail near the firewall. See a hose coming up and connecting to it? That is the inlet or feed fuel line connection. On the other end of the fuel rail, coming out of the left side of the regulator is the outlet or return fuel line. Both lines have quick disconnect fasteners. If you have not dealt with these before, this is a good time to start because these two are right where you can get at them. These fasteners are used on several components of your Jeep such as transmission line connections. Place a rag under the inlet/feed connection. With your fingers, squeeze the plastic tabs sticking out of the connection compressing it against the metal tube protruding from the rail. While compressing, pull the hose away and turn the opening upward to minimize fuel spillage. Look for two small orange o-rings and a small plastic spacer. This is where the pick comes in handy to retrieve the small parts from the hose opening. If you're lucky, all three items are on the tube where you can see them. Dispose of soiled rags appropriately.

5) Repeat step four on the regulator side outlet/return fuel line connection. The hard fuel line will work back about an inch and barely clear the opening to the regulator. Take a look where this hard line goes . . .right into another quick connect fitting on a flexible hose. Is it leaking? If so, use a repair kit on it as well. Remove the vacuum line from the right side of the regulator and twist out of the way.

6) Scan the fuel rail assembly and see what crosses over it that might get in the way of removal. I disconnected the accelerator cable on the aft side of the throttle body. Just pull the black horse shoe shaped connector to the right side of the vehicle and off the ball stud. Squeeze the black mounting connector allowing the cable to pass through the mounting bracket (I used a small set of pliers here). Lay cable out of the way. Disconnect other crossing connectors as necessary making sure you remember (label) where they go.

7) Now remove the four 13-mm bolts holding the rail to the manifold.

8) Disconnect the wiring harness from each individual connector. You did read the part about labeling these didn't you? There is a small safety clip holding the electrical connectors on tight. Carefully use the pick to remove these clips and safeguard them. The wire connector comes right off after the safety clip is removed.

9) The rail assembly, regulator and six injectors are all yours now. Carefully wiggle each injector back out of its hole in the engine head. Slightly twist and turn the whole assemble until you get it free. Some manuals recommend removing the accelerator cable bracket to facilitate removal; however, I have not found this necessary.

10) Take a look at how the injectors are attached to the rail. There is a very special clip holding each one to a little silver cup looking thing on the rail. These clips can be removed by hand and the injector pulled free from the rail. DO NOT loose these clips. They don't sell them separately from the rail assembly ($$).

11) Once the injectors are loose, you might as well check each one for proper operation. Check resistance across each injector's connections. You should read 16 ohms. Another way to check operation is to power the injectors with 12 volts. You should hear a click as power is applied. Check each opening for obvious blockages. Remove the old o-rings by rolling them off with your fingers.

12) Install new o-rings by rolling them on. Apply a light coating of Trans-lube to the outside of ALL the o-rings. Reinstall injectors in fuel rail (they should be rather snug going in and feel tight). Note how the clips fill the groove in the injector and go over the lip of the little cup.

13) Might as well replace the regulator o-ring since we have everything apart. You'll need a small torx head driver to remove the two screws holding the regulator in place. Twist and pull apart to remove the old o-ring. Roll on a new o-ring and lube before assembly.

14) With the rail assembly back together, wiggle it all back in place. Line up each injector with its hole and push evenly to seat each one. Make sure each is seated all the way to the first large bulge on the injector.

15) Install the fuel rail bolts to about 20 ft-lbs. It is a good idea to put a little Permatex Anti-Seize on the threads to fight dissimilar metal bonding.

16) Install your quick connect repair kit carefully. The connector, o-rings, and spacer should "click" into the female side of the connection. Then slide the quick connector fitted side of the line over the other end until you hear another click.

17) Hook up the vacuum line to the regulator, plug in each injector and install their safety clips, and reattach the throttle cable (as applicable).

18) Look over the entire area for anything left unhooked or that looks out of place. Reconnect your battery ground cable and put the gas cap back on. Make sure any spilled fuel is cleaned-up and disposed of properly.

19) Enlist the help of an assistant. Leave the hood open and observe the injector area while the assistant turns the ignition key to power, but not to crank the engine. This will cause the fuel pump to pressurize the system and should quickly identify any leaks. If no leaks are observed, have the assistant start the engine. If any leaks are noticed immediately shut-off the engine, clean-up the fuel, and troubleshoot your leak.

By - David Jones