I have a 98 Grand Cherokee that stalls and the fuel gauge hasn't worked right since I got the vehicle (used) in June 2012. It runs for approximately 45 minutes till it heats up, then it stalls like older carbureated vehicles would have done when they vapor locked. I have to wait 45 minutes to an hour till the vehicle cools off, then it runs again, till it warms up and stalls again, I took it to a mechanic who had to use an older scan tool to read codes, and he put a pressure gauge on the fuel line from the tank and pump to the engine, and told me it was reading 20 PSI or less, and the pump was bad and would have to be replaced. The tank has to be removed, gas drained, old pump removed, new pump installed, tank put back in, and pump wired back and plugged in, then see if this solves the problem.
I have also been told the crankshaft position sensor might be bad and have to be replaced as well as this causes the kind of failure I have been experienceing to happen as well. Is this a correct diagnosis (es) or is there some other cause for it stalling and not running for 45 minutes as it has been ?

 

Start with the sensor .....notorius problem

 

I have seen a bad PCM do the same exact thing. When it stalls check the fuel pressure as soon as the engine dies. If you have fuel pressure (not sure of the spec, but somewhere between 40 and 50 psi) and the engine still does not start, you have another issue. Checking for spark would be the next thing to check.

 

Agreed. If you find there is little to no pressure though, check for ground and voltage at the pump. If you have ground and voltage, the pump is sure to be it. If you are missing voltage, you will have to start back tracking the wiring to find where the problem is. I can probably get the wiring diagrams from work and upload them if needed.