I going nuts with this issue on my daughters 2000 XJ

[reyesryder]

Hi eveyone,

In the last 5000 miles, new O2 sensors, new injectors, and new plugs. Jeep has an issue where it almost acts like the exhaust is plugged. Starts fine, but drive it a few blocks and it starts losing power to the point you have to pull over and it will hardly idle. Shut it off and restart it and it’s fine. Start driving and it’s the same issue. No CEL. Just installed a new CAT, TPS, checked fuel pressure which is at about 45, but no luck. Any ideas?

[Skruffy]

Vacuum lines can be a problem. typically not exactly your symptoms but easy to check and fix if in fact they are leaking.

[Anak]

Details such as what year your XJ is could be helpful. It is one thing if you have a Renix era Jeep, another if you have an H.O. and yet another if you have OBDII.

The use of a scan tool that can show you what the sensors are reading would be helpful here, if it is an option. For OBDII it is an easy option, but for Renix not quite so easy.

[maxbraketorque]

Could be any number of things, but my first thought is crank position sensor. However, since fuel pressure is low (it should be 53 psi), perhaps the fuel pump is failing. Have you logged the fuel trims? If the fuel pump is going bad, the fuel trims will go strongly positive and stay there.

[8Mud]

Just something I would look at, rear 02 sensor wire cooking on the exhaust, front O2 harness cooking on the header, especially if you have swapped out a water pump or steering pump. Sounds like as soon as the motor switches over from open loop to closed loop the fuel trim turns to crap. Might also want to take a look at the O2 sensor heater fuse.

[Tim_MN]

The symptoms do not suggest vacuum lines or fuel pressure as the primary suspect for the symptoms. 49 +/- 5 psi is the specified fuel pressure for 97-01.

As already suggested, the onset of the symptoms seems to be as the PCM switches from Open Loop to Closed Loop and monitors all the engine sensors. You should suspect a faulty engine sensor, or wiring issues to an engine sensor, and O2 fuses. Test the engine sensors, especially the Coolant Temperature Sensor and the O2 Sensors. Inspect all the sensor wire plugs for chafed or melted wire insulation, and corroded, bent, or pushed back wire pin plugs. Look especially closely at the wire harness and wire plugs for recently replaced sensors.

Confirm that the O2 sensors are NOT Bosch or auto parts store generics. It is well proven that Bosch and auto parts store generic O2 sensors can easily cause drivability issues. You should only use NTK O2 sensors.

All the other engine sensors should be genuine Jeep parts. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a " Lifetime Warranty ". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

[maxbraketorque]

Even if fuel pressure spec is 49 +/- 5 psi, I'd still watch fuel trims from startup to stall.

[bruceb]

I would suggest that once the vehicle stalls, pull the spark plugs and see how they look. This may help direct you into what direction of diagnostics to follow.

• Light tan spark plug: Good mixture.
• Dark brown or Black Spark Plug: Too rich
• Black, oily Spark Plug: Oil fouled (see valves or piston rings.)
• White, no color on spark plug: Too lean.
• Good running conditions: If everything is good, the spark plug should have a tan/light brown color.
• Rich running conditions: If your engine is running too rich, the spark plug will be black and sooty.
• Lean running conditions: If your engine is running too lean, the spark plug will be white.
• If the spark plug is black and oily, they are oil fouled.