Grand Cherokee 1998 problem, help wanted!!?

check fuel pressure,plug wires,injectors,computer freeze frame,and miss history.tap on computer and see if smptons change.

back fires when it's hot engine idles unevenly. Sounds like you have a cyclinder that isnt' firing. Since it's when its hot I'm gonna say when the engine heats up and expands somethign is shorting out. Backfiring means there is unburned fuel in the headers. So i'm gonna guess and say bad plug wires, or caps, or distributer cap. do a spark gap test when the engine has the problem. or just pull each plug one at a time when you pull a plug and the engine shows no change thats your culprit.

Sounds like a misfilre. Could be a bad ignition control module, ignition coil, or the computer. You should get a mechanic that will diagnose your vehicle when it gets hot to find out what is wrong and not waste your money just swapping out parts.

are you loosing oil too? They've got a problem with the intake plantum leaking oil into combustion chamber and causing a spark knock. you should notice it blowing blue smoke out the tail pipe when this happens. If not, then you may have carbon built up on the piston and causing it to pre detonate.

If it's the oil leak, the intake plantum gasket will have to be replaced.

If it's the carbon built up, you can pure a spoon full of water down the intake to knock of the carbon.

Do a compression test

You may have a burnt valve

After getting Hot if you have a burnt valve it won't seat