Newbie here. Just playing with new to me '89 with 70k on it. Going over a two-track pass at about 11,800 fuel pump got noisy. I stopped on the down side to check, opened fuel cap and tons of pressure and HOT fumes. Filler pipe and tank very hot. After about 30 minutes going down, noise got quieter and stopped. I opened the cap and normal pressure, but filler completely cool. Never noticed any change in engine through all this and no over-heating according to temp gauge. What the heck is going on there?

 

The fuel tank is supposed to be vented via the evap system, which routes vented air thru the charcoal canister, and when engine is running, the engine sucks in fumes abosrbed by the charcoal canister.
Seeing as your tank got pressurized, Id say the vent is not venting. you got a clogged vent. A clogged vent will also cause fuel pump problem as the pump must work very hard to pull fuel out of a sealed tank that can not vent. This may cause the pump to over heat, and fail, and loss of fuel pressure. in worse case, the pump may even cause the tank to crush, as a vacuum is pulled as fuel is removed with no way for air to enter.
as for heat, conceivably a tank with blocked vent can become under positive pressure is the fuel is heated, either by high daytime temperature, or perhaps an over heating pump.

Run an evap system test,

I once had a spider nest block the charcoal can vent in my van, cause the fuel to not be delievered no matter how hard the pump tried as it fought pulling a vacuum on the tank.

In mean time, leave the fuel cap loose, and do not fill tank completely. The loose cap will allow her to vent so you can drive withlut pulling a vacuum inside the tank until repair can be made. dont fill to max with loose cap to minimize fuel spill.
even with cap tight, do NOT park inside garage until repair done. liquid fuel expands a lot when heated, if your vent dont work to release pressure, and say you have a tank full of cool gasoline, and you park in a warm place, pressure will build up, more so if your tank is full. unvented the tank will pressurize, and this can cause enough pressure to perhaps blow off a hose or wreak a seal, then you may have a flood of gasoline, thus park her outside!

anyway, your evap system per your description appears to be clogged. dirt or spiders in the vent hole, or a kinked evap hose can be the problem.
Check your year specifis repair manual as different hear XJs may have different evap systems.
Often there is a basic diagram of the evap system on a decal in the engine bay, that may help you locate the hoses and charcoal canister. more advanced newer vehicles may have electrically activated vales or even little vacuum pumps in the system for better operation or diagnostics as new cars will even generate a check engine code is the system detects a leak, even a loose gas cap can be detected, but your old XJ does not have that whiz bang stuff, and I think is a totally passive system with no electronics to go bad.

So check it out. hopefully a simply done fix like block vent or pinched hose.

Use great care around fumes, as gasoline fumes is explosive! Work on your fuel system outside, not in the garage unless it is well vented, no pilot lights nor sparking electric things nearby. Do not ignore gas fumes, kaboom!

 

Tons of information here robsjeep...thanks so much, this is very helpful! Any thoughts on elevation playing a part in this?

 

High elevation should not be a problem. Had my XJ and other vehicles at 10,000 feet, no problem I am sure many an XJ drove up Pikes Peak without this issue. You have a defect or clog someplace.

 

fuel pressure regulator.