Fuel smell from under the hood, or out the tailpipe ? The fuel rail can leak, and the fuel injectors, or fuel injectors O-rings can leak. Fully inspect the fuel rail, fuel injectors and injector O-rings for leaks. If you un-install or replace the injectors, buy new injector O-rings and lubricate them with engine oil before re-installing them. 49 +/-5 psi is normal fuel pressure, and a common problem is a failed fuel pressure check valve on the in-tank fuel pump assembly that allows fuel pressure to drop when the engine is off.

An unstable idle might be a dirty throttle body, or a dirty/faulty Idle Air Controller (IAC). Clean them both. Replace the IAC with a genuine Jeep part if necessary.

Cleaning the Idle Air Controller (IAC) :

Purchase sensor safe Throttle Body cleaner spray.

1. Remove the Throttle body from the intake manifold.
2. Remove the IAC with a TORX 15 driver (2 bolts)
3. Gently wiggle out the IAC from the throttle body
4. Clean the IAC with Throttle Body Cleaner (not carburetor cleaner). Usecleaner, a rag, and a toothbrush. Be gentle; don't twist or pull on the IAC pintleas it is fragile and can be damaged easily
5. Also clean the IAC housing in the throttle body
6. While you have the Throttle Body off, give it a good cleaning also.
7. Reinstall IAC, the Throttle body, and check idle quality.

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Thank you, I'll try that tomorrow before work.

 

If I can hear flooding back into the tank after I shut off the engine, would that be the check valve? Also would that cause the misfiring?

 

Gurgling at the tank after shut-down is normal, and may or may not indicate a faulty check valve. IF there is 48 psi of fuel pressure while the engine is running, something else is causing the misfires.

When a 1997 to 2001 Cherokee won't start on the first try day after day, the first thing to suspect is a failed check valve on the fuel pump. The fuel pump check valve is supposed to hold pressure in the fuel line while the engine is off. The check valve is located on the fuel pump and located inside the gas tank. A failed check valve allows the fuel to drain back to the tank. This results in one or more of the following symptoms:

SYMPTOMS
• Longer than normal cranking times
• Never starts on first try, almost always starts on the second try
• Rough idle fora few moments of idling
• Rough running for first ½ block of driving
• Little or no fuel pressure at the fuel rail test valve similar to this -

1- Key in on position; fuel pump primes for 2 seconds then stops. 0 PSI
2- Cranking over the engine. 2-3 PSI
3- Engine starts and idles for 20 seconds. < 5 PSI
4- Engine idles and fuel pressure creeps up to 45-50 PSI.

POSSIBLE CAUSES
• Failed check valve on the fuel pump in the gas tank.
• Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.

Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail, and you may be dealing with a bit of vapor lock as well, especially in warmer weather.

1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.
2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank.Watch the pressure gage and see how long it takes to loose pressure.

If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.

There are a few solutions to the problem -
1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.
2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.
3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.

You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.

If you do replace the fuel pump assembly, purchase a high quality OEM style pump assembly such as Bosch or Carter. Some cheap aftermarket fuel pump assemblies, like Airtex, and Precision don't hold up and will fail completely within 12-18 months.