I have a 2002 WJ 4.7L V8 2WD with 74000 miles. Recently, when it has been sitting for more than 15 minutes, it is hard to restart. This happens whether it has been 15 minutes or 15 hours since it was last turned off. When I try to start it, it takes about 10 seconds of cranking before it fires up. It turns over normally (no problems with starter or electrical system). Once it is cranked it runs perfectly. No hesitation or bucking anywhere from idle to full throttle. Battery voltage is fine, gas is of known good quality. Still has original fuel filter. Spark plugs were changed 10,000 miles ago. Dumped trouble codes and found none.
I did a little troubleshooting to try to narrow down the problem:
I hooked a fuel pressure gauge to the rail via the schrader valve which is located over the passenger side valve cover. When I did this the jeep had been sitting for about 2 hours. The gauge indicated ZERO fuel pressure. I turned the ignition switch to ON but did not start the engine. Fuel pressure remained at zero. I cranked the engine. Took about 10 seconds to start. During cranking, fuel pressure remained zero for about 3-4 seconds, then started building up gradually. When it reached about 20 psi, the engine caught and started running. Fuel pressure went rapidly to 52 psi and stayed there. Engine ran fine.
I then shut down the engine. Fuel pressure rapidly dropped to 10 psi (like in about 3 seconds). From there, over the next 10 minutes it slowly dwindled to zero.
Attempting an engine restarted yielded the same results as above. This time, I stopped the engine and as soon as the fuel pressure dropped to 10 psi, I attempted a re-start. The motor cranked perfectly. I shut down the engine.
The fuel pressure was at 10 psi at this point. I turned the ignition to ON but did not crank the motor. The fuel pressure jumped to 52 psi and then immediately fell back to 10 psi. I then turned the ignition to off. I then repeated this several times (again, not cranking the motor). Same deal... pressure jumps when switch is ON but drops immediately to 10 psi.
This time I waited 10 minutes until the pressure went to zero. I turned the ignition to ON but did not crank the motor. The pressure stayed at zero. I turned the ignition OFF and back ON again. Still zero. Again I went OFF-ON. This time the pressure jumped to about 5 psi and stayed there. Another OFF-ON cycle got it up to 10 psi. I then cranked the motor and it started fine.
Ok, I know that was long, but obviously I have a pressure bleed-down problem somewhere. I checked around the motor and under the jeep and on the tank and didn't see any obvious leaks. I assume that means the leak is either internal to the tank or a fuel injector leaking down. How can I rule out one or the other or move forward in the diagnosis of this problem? I don't have factory service manuals right now but I ordered some...
Also, I saw this TSB on wjjeeps.com, but it is listed as only applying to 99-2001 jeeps... although it sounds awful similar to my problem: