I've been having hard starting issues for a while. At first the jeep would crank a few seconds longer than usual on warm starts, sitting for a few hours or less after running. Felt as if it wasn't getting fuel. Not related to the problem I installed some 784 injectors with new O-Rings. This changed the hard start issue from just a long crank to "stumbling" on warm starts. It will crank and stumble like its only half catching and then will finally fire up. It also fires up extremely quickly on cold starts. More quickly than normal, I barely touch the key and it fires. I'm thinking I have a fuel leak somewhere that's throwing off the mixture when I start but I can't detect any leaks. Any ideas? I've had heat soak issues before and this does not feel like heat soak.


Plugs are new
Compression is good
Starter is good
Crank sensor is new

 

Still could be heat soak. The 00-01 XJs are particularly susceptible to this issue.

You can get a hold of a fuel pressure gauge and perform some advanced fuel pressure testing to try to see if you have any fuel leakage past the injector into the cylinder. The factory service manual outlines this procedure.

 

Have you reset the PCM? Very easy to do - I would try it again to see if it makes a difference.

1. Disconnect both battery terminals (or just the positive if you are comfortable with DC power).

2. Ground the positive cable (and negative if you removed that) for 60 seconds. I usually hang the positive battery terminal on the AC Compressor bolts and leave the negative terminal connected to the battery.

3. While the PCM is discharging, induce a load on the system to make sure it's discharged (turn on the headlights for a few seconds)

4. Reconnect positive terminal. Turn key to "run" but don't start the engine. Turn on headlights for 10 seconds (apparently this will "erase" the PCM adaptable memory).

5. Turn headlights off. Turn car off for 30 seconds.


I usually do it twice to make damn sure the PCM gets reset. I chased a hard start issue for a while, "thought" I reset the PCM but 3 weeks later I did the above and resolved the issue.

If all else fails, try heat shielding the injectors, rail, and above the intake manifold. DEI sells a kit for the 4.0 that does exactly that.
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