04 4.0 struggling to start when warm
 

So my 4.0 wj has some starting issue. When it's cold it starts just fine, but say if I was running errands and starting and stoping frequently it starts to struggle to start up, and the other day even it sounded like it was misfiring for a minute after I started it. Any ideas?

When you say it struggles to start, do mean it turns over slowly, or has an extended crank time before it starts?

It's a little more of a delayed start

So extended crank time, and the crank slows down when warmer. When truck is cold it fires right away with no struggle

Start with having the battery load tested, then check the charging system, then see how many amps the starter is pulling when you're cranking the engine over.

Brand new battery starter and starter relay, replaced twice in fact

Check the fuel pressure when it's acting up.

Okay, here's something my 2000 WJ is doing and IDK if it has anything to do with your problem but I'm going to throw it into the mix anyway.

I deliver newspapers and I get to the distribution warehouse at 11:30 PM to get a good fast-loading parking spot. The truck doesn't come with the papers until about 2:00 AM, so I sit there, trying to stay warm by running the engine and heater at intervals during that time. It started this crap last winter, but now it's worse. If it's shut down long enough for the o2 sensors to cool, it runs ragged until they warm up. The engine is fully warm, but the PCM thinks it's cold and sends a rich mixture command to the injectors. As soon as they warm, it's idles fine. I'm pretty sure that's what it is because if I give it some throttle, it smooths out sooner. I've got 182K miles on the originals, so maybe I should change them, huh? I've got the CA emissions with the split downpipe and 2 small converters.