Brief misfire/stumbling/rough idle after starting XJ when hot.

Just as the title says, my XJ runs funny for a short period of time after being restarted when the engine is hot.
I live in AZ. The car does not over heat when its in operation, not even when in stop-and-go rush hour traffic or when stationary and idling. The temperature sits dead center of the gauge, just like it should.
I notice the problem only in very specific circumstances, but it is reproducible very easily. After driving the car for a period of time, and then briefly stopping it (2 - 10 minutes depending on outside temperature), and then restarting it again, the car idles rough and idle speed varies, vibrates a lot, sometimes sounds like it wants to quit. Usually, it evens itself out within a minute, or pressing on the throttle and revving the engine briefly seems to cause it to go away as well. Every now and then however, when you give it gas under these circumstances, the engine sputters up as it revvs and feels like it has no power for a second, but then quickly recovers and runs normally again.
The last time this happened, the check engine light came on. The code was "Cylinder 3 misfire detected". I cleared the code and it hasn't come back since.
There is no white or black smoke from the tail pipe. No funny smells in the exhaust. I cannot detect the smell of significant amounts of unburnt fuel in the exhaust either.

I'm stumped. Any ideas?

My XJ is a 2000 Cherokee Classic 2WD, 4.0L I6, 195,000 miles.

Search for "Heat soak" and you'll have lots of reading to do regarding this issue on your 2000. The factory fix is a useless wrap for injector number #3. Most people have had limited to no success with this. The primary solution for this problem is to install an e-timer on your electric fan so it runs for a few minutes after hot shut down.

Heat soak, and probably a failing Check Valve also.

When your 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 in 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 for a 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 a leaky injector.

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, don’t hold up and fail completely within 12-18 months.

This is why I love Naxja.org - I have started experiencing symptoms as described (long cranking, rough idle/stumble), and in less than a minute and on the first page of posts, found this. Thanks Naxja.org, thanks Tim_MN.

Mine does the same but I noticed its only when the electric fan comes on. Whenever it comes on the whole jeep shudders and wants to quit but as soon as its off its fine. Might replace my battery or alternator because I don't think she can handle the fan, stereo,sub, etc. If anyone else has ideas let me know too. Thanks