I have a 1999 xlt 4.0 extended cab auto. I have to turn the key twice to start it after it cools down. It sputters when It starts like it wants to stall and you have to pump the gas to get it going. The only code that pops up is an o2 sensor. I changed plug's wires all my fluid's and fuel filter. No ideas on what it can be. Maybe losing the prime in the fuel line?

 

if you haven't figured it out and you're loosing coolant in the reservoir I'd say head/ headgasket that could cause an o2 to go bad too. but if your not noticing that or other head symptoms then perhaps you have clogged injectors or your fuel pump maybe going bad. how long had it been since you changed the fuel filter previously?

 

your fuel filter is nearly plugged up / or your fuel pump is failing