Sacnasty

Hi guys I have a 1995 XJ 4.0. Here recently when I crank it up let it warm up and start driving down the road all of the sudden it starts spitting and sputtering running rough like it has a foul plug. I let off the gas then give it gas again it runs fine for a few seconds then start spitting and sputtering again I just repeat this process a few times and it starts running fine. It's got practically new cylinder head and a cold air intake that's really the only modification to the motor. Also has new plugs that are only a few months old and wires and distributor cap. Seems like something is trying to go out any suggestions on this would be helpful

tjwalker

Did you have this issue BEFORE you replaced plugs, wires and cap? If not, it is a possibility that one of the new parts are suspect. Also it is a good idea to replace the rotor whenever replacing the distributor cap.

Start with simple things first. Test fuel pressure. Try to recreate this symptom in your driveway while you watch the fuel pressure gauge. For a 95 4.0 liter engine, the fuel pressure spec is 31 psi. Then disconnect the vacuum line leading to the fuel pressure regulator under the hood and the pressure should jump to approximately 39 psi. If there is any raw fuel in that vacuum line, the fuel pressure regulator will have to be replaced.

If fuel pressure checks out okay, I would start testing (don't just replace them on a hunch) some of the engine management sensors like the throttle position sensor, coolant temperature sensor, map sensor.

Good luck and keep us updated.