Pulleeeze help!! My '98, 4.0, 6 cyl. Cherokee (Sport? Bought used. Has Police Package, no insignia) starts, stalls, starts, stalls, runs, keeps running, stalling, running for a mile or so, then runs for a while longer then tries to stall again and after a few miles, runs just fine. After sitting for a few hours the whole cycle repeats itself. Tried STP Gas Treatment and Sea Foam fuel system cleaner. Computer check shows no codes. Check engine light not on. This started after two straight weeks of rain, if that's a clue.

 

You may want to check your fuel pressure at the fuel injector rail test port.

You can rent, deposit refund, a fuel pressure test set from an auto parts store.

Your fuel pressure should be around 49 psi. With the test gauge hooked up, start the engine and check the fuel pressure at idle, then advance the throttle and check the fuel pressure with the pump under demand.

Edit: The PCM does not monitor fuel pressure so you won't get a CEL.

 

I have an 98zj...It does the same thing... especially on cold days... It back fires also...have changed the dist.cap, rotor button, put in oe plugs, mopar plug wires and am preparing to change the crank pos. sensor... should I change my fuel pres. sensor/fuel filter too??... any help appreciated.

 

Your suspicion regarding dampness may be right on the mark. The behavior could be due to moisture trapped under the distributor cap and/or old spark plug and coil wires. If this is true then after a few days of warm dry weather the condition may just go away. I hate mysteries like this as I imagine you do too, it's best to attack it now while it's in your face, because you don't want the problem to rear it's ugly head when you can least afford to deal with it.

Try this simple procedure. Remove the distributor cap and inspect for moisture, wipe it out and fog it with WD-40, shaking out any excess before restoring it. If the problem is due to the wires, old or new, they may benefit when sprayed with WD then wiped down followed by a coating of dielectric grease. If they're old then the real answer to that part of the equation should be obvious. If you choose to replace them then treat the new wires with dielectric grease anyway.

 

Does it idle better and stay running when your engine gets to temp? Might be your idle air control(iac)

 

Did you get to the bottom of this one?