98 Jeep Wrangler Engine Troubles

Hi, I'm new to the forum.

I have read numerous posts similar to my engine's problem, and haven't found a solution yet. Here's the trouble: Burning out plug #4, running very ruff, idles okay most of the time.

Vehicle type: 1998 Jeep Wrangler 2.5L I4 w/Multi-port fuel injection
Have performed the following:
Compression test; Cylinders #1 & #2 - 130 lbs. pressure
Cylinders #3 & #4 - 150 lbs. pressure
New TPS (Throttle positioning sensor)
New IS (Idler sensor)
New Plugs (3 sets in last 3 weeks)
New Wires, cap & rotor
New coil (stock)
Put Gas Treatment in the gas tank
Diagostic by mechanic showed no electrical error codes (He suggests it's possibly mechanical)
Check engine light is not currently on. It has been on, but has gone off.
I don't believe it's a head gasket with the cylinder pressure readings like they are.

Anyone have an idea of what more I should do or try?

CRANDY

Crank position sensor and Camshaft position sensor is what I'd think of.


-edit- after further thought, you could have a fuel delivery problem so check the fuel filter and pump output.

Thanks for the suggestions. Actually I pumped the gas out of the gas tank (about 11 gallons) and refilled it with premium gas. She is running like a top now. Hard to believe the trouble was caused by bad gas.

Good catch...glad it was only some crappy gas.