1993 XJ6 4.0 Fuel 39 / Fail 39 Engine seems to run fine. What is this code about? Problem occurs after driving at least 7-10 min's. Under that and no Fault Code / Chk Engine light.

sounds like fuel delivery problem, have pep boys tell you what codes are if you dont have diag tool. if its fuel pump, easy fix, under car, not in tank

Someone will need to check it over when it fails to start. You need to know if it is not getting fuel to the injectors or spark to the plugs.

Someone would need to check the fuel pressure with a gauge and replace the fuel filter to eliminate the pump. Assuming the check engine light is not on, it could be a vac leak or other problem.
The most common problems are a leaking EGR valve or faulty throttle position sensor, but those components should make the check engine light come on if they fail.

Are you sure the battery didn't fail, these new sealed batteries do this excat thing, one min they are fine, then dead.

Hello
The engine and automatic transmission in this vehicles drive train are fully electronically controlled by a computer called the PCM (Power Train Control Module). Whenever a problem like this occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump, engine coolant temperature sensor and MAF sensor for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL A TRAINED TECHNICAIN HAS DIAGNOSED THE PROBLEM TO AVOID SPENDING YOUR HARD EARNED MONEY ON PARTS THAT MAY NOT CORRECT THE PROBLEM

Is the check engine light on ?
It sounds like the engine temp sensor is not right, but if that were true you should have a check engine light and a code for the sensor.
Have you checked fuel pressure ?

Hello
The engine and automatic transmission in this vehicles drive train are fully electronically controlled by a computer called the PCM (Power Train Control Module). Whenever a problem like this occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump, engine coolant temperature sensor and MAF sensor for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL A TRAINED TECHNICAIN HAS DIAGNOSED THE PROBLEM TO AVOID SPENDING YOUR HARD EARNED MONEY ON PARTS THAT MAY NOT CORRECT THE PROBLEM

When this stall or fails to start occurs have a pressure gage hooked up to the fuel injection pressure test port (top of engine in the pipe that supplies the fuel to injectors) and see if you are losing fuel pressure.

With it just stalled you need to isolate the problem to fuel spark or compression to know that to do next. no spark inghtion modules fail. no fuel fuel filters and fuel pumps fail. Compression cooling system problems ( no fan) raditor coolant low) therostate stuck clossed. find something and reply and I'll be glad to respond to your post.

chek filters for fuel on frame and in tank