2000 4.0 dies when at operating temperature

[Air2jjs]

Hello All,
I've been working on this annoying problem that has morphed into a major issue.

Typical long crank issue. Previous owner did not address the problem. I would not have bought the Jeep with this problem but my spouse did.

-I changed the entire (Delphi) fuel pump/ sending unit/ pressure regulator.... no effect, still long crank
-Cleaned injectors... no effect, still long crank
-Replaced fuel rail (Summit) and all injectors... starts immediately hot or cold, but with new problem. Driving after coming up to temperature, acts like its running out of gas and dies.
Will not re-start until cool.

Logic says reverse the last thing you changed

Removed Summit fuel rail and re-installed the OEM fuel rail with the new injectors. Result= still starts easily but when warm, dies. Yes, I have increased the area of the heat shield near the injectors and wrapped both fuel rails with heat cloth wrapped with high temp metal tape. I also wrapped the fuel line as it rises from the frame area passing by the exhaust.

Thoughts? By the way, this is an almost perfect Sahara 2000 model (86,000 miles) but I have spent more time and effort on this than any other (well, except for my Grand Wagoneer)

 

[Jerry Bransford]

If it runs ok when cold my guess is you have a bad O2 sensor that is causing the PCM to give a way too rich or way too lean fuel condition. The PCM only refers to the O2 sensors when the engine has started to warm up, it ignores them when the engine is cold.

If you replace the O2 sensors, install ONLY NTK, NGK, or Mopar (all of those are made by NTK) O2 sensors. Do NOT install Bosch sensors as they do not run correctly in a TJ due to it requiring a different bias voltage than what the TJ provides. No aftermarket O2 sensors either.

 

[Air2jjs]

Thanks Jerry

 

[TrailYacht]

Are they factory replacement injectors? Maybe pcm is using the mapping from old injectors have you done a hard reset via grounding capacitors? Jerry is still most likely right here lol

 

[Air2jjs]

TrailYacht, I did purchase OEM injectors but maybe what I removed were not and mapping is incorrect. How do you do the hard reset? I'm searching the forums now.

 

[Air2jjs]

Reset the PCM, no help. Looking into the O2 sensor now.

 

[Air2jjs]

O2 sensor no help. Now I’m wondering if I got a bad load of gas. Also changed out the throttle body, TPI, air flow and idle solenoid. Still warms up to operating temp… then 7 min later, dies.

Next steps
-drain all gas
-replace cam sensor (failing when hot?)
-replace crank position sensor

After that, truly at a loss for what could be wrong.

 

[Jerry Bransford]

O2 sensor no help. Now I’m wondering if I got a bad load of gas. Also changed out the throttle body, TPI, air flow and idle solenoid. Still warms up to operating temp… then 7 min later, dies.

Next steps
-drain all gas
-replace cam sensor (failing when hot?)
-replace crank position sensor

After that, truly at a loss for what could be wrong.

Start with a Mopar crankshaft position sensor, no store brands there. Or at least a premium brand of CPS like NAPA sells.

 

[Air2jjs]

Thanks Jerry

 

[Scotty555]

Air2jjs did you figure this out? I am in a very similar issue, 3 years later..​

 

[macleanflood]

Air2jjs did you figure this out? I am in a very similar issue, 3 years later..​

Might want to start a new post and tell us more about your Jeep.

-Mac