Ive had this problem for awhile now. After my 2007 3.7l Grand Cherokee has warmed up and I shut it off it will not start for about 20 minutes. Just cranks. Ive replaced the spark plugs, the crank shaft position sensor and the cam sensor. No effect. There are no codes. Starts cold no problem. The problem seemed to disappear after I changed the water pump due to a leaking gasket and changed the coolant. But is back now after a few months. ASD relay was changed 50000 km ago but that was before I owned it.
Any thoughts?

 

Alas I cannot post links yet but I found a really good thread on this over in the Jeep forum. Here are the take aways:

Poster stated:

I would say it definitely sounds like vapor lock . i checked the service manual and unless you have a code to point to a specific part (possibly ambient air temp sensor or asd relay) all i can suggest is test or replace the purge solenoid .If the vehicle is already in a hot or closed loop state , the purge solenoid should activate and it sounds as if it is not for whatever reason . I can't post pictures from my service manual (they are easy to find on-line), but here's the description

SOLENOID-EVAP/PURGE
DESCRIPTION
The duty cycle EVAP canister purge solenoid (2) is
located in the engine compartment attached to a
bracket.
OPERATION
The Powertrain Control Module (PCM) operates the solenoid.
During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When
de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.
The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During
closed loop operation, the PCM energizes and de-energizes the solenoid 5 or 10 times per second, depending upon
operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the
amount of time the solenoid energizes. The PCM adjusts solenoid pulse width based on engine operating condition.

Another poster stated that ethanol based fuels could cause a problem. In the case of this op he drained his tank and filled up with a non-ethanol fuel and did not have a problem with that tank of fuel. No more heat soak issues. Of course after that post the op never posted back so there's no way of knowing if the issue came back after one tank but since there isn't much involved wrench wise in running the gas out of your tank and filling up with a non-blended fuel it might be worth a shot. Just keep a full gas can handy during the run down!

 

Thanks for the info will investigate. I inspected the ASD and fuel pump relays and did not have a no start fault after engine warmed up yesterday.

 

I tested the solenoid and it will actuate with 12v applied. Now does it get a signal when the engine is hot or at a certain rpm I'm not sure. Still burning my ethanol blend.

 

Sometimes just the mere pulling the relay and re-inserting it polishes the contacts enough to make it work! After that happened to me, I pulled them all and used a pencil eraser in the relay's blades and contact cleaner on the sockets.