Hey there, I've got 266k on my '99 XJ and it's had an odd issue since I purchased it. Upon acceleration it will randomly drop RPMs and lose power, and it sounds like the engine is struggling to run. Two things will make it stop, flooring the gas, which occasionally makes a "pop" sound, or letting off the gas for a second. Fuel pressure tested at 45PSI, all six cylinders tested at 145-160PSI compression (from my own research these numbers are within tolerances). The problem is completely random, although seems to be happening more often.

The only thing I can guess at this point is fuel pump, fuel filter, or injectors. What do you guys think?

 

i'm betting on clogged fuel filter or clogged/malfunctioning injectors. Change the filter first and see if that fixes your issues. If not, remove the injectors and clean them manually (lots of guides on how to do this). It may be worth it to replace the micro filters at the same time.

 

hi, i think you should try and check the distrubitorcap, rotor, leads and spark plugs.