I have a 98 jeep grand cherokee. i just bought it recently and when buying it the guy said the catalytic converter was bad. hooked it up to a code reader and its said the o2 sensor was bad. i changed the oil in it yesterday and afterwards it started messing up it will crank but almost immediately shut off. ive talked to some people about it and they named off a couple of things it could be. the o2 sensor, catalytic converter, oil sending unit, or the ecu. havent replaced anything yet want to get some more opinions first.

 

Sounds to me like a security system issue. Try locking and unlocking the door with the key a couple of times. My 97 had this problem and the horns were burnt out so the only way you could tell the system was engaged was that little red flashing LED on the dash top. Mine reset with the key fob. Using the key door locks was out because the tumblers were frozen.

When the system is engaged, it will allow you to start it, but the ASD relay will shut off the fuel pump and spark within a second or two after starting.

Welcome to CF!

 

I'll give it a try but I think I found the problem. I got under it today and unplugged the o2 sensor tried cranking it and it stayed running for about 5 or 6 seconds and shut off

 

It's possible the 02 sensor is shorted, but now the PCM isn't getting a signal and is shutting it down.

 

Yea that's what I was thinking. I was looking around on the Internet and some jeeps like mine have a recall on the catalytic converter