So I swapped a 2000 jeep 4 liter engine into my 95 because it blew a rod and we changed and checked every sensor from my old engine to my new engine. and it still doesnt run right and the check engine light wont turn on and it blows black smoke. and when it starts to run rough the fuel pressure starts to climb. but what is weird it runs for about 15 seconds or so the way it should than it starts to act up and idle really rough what could cause that?

WHen you swapped the engines, did you take notice that everything was the same? Sensor locations, CPS, PCM Connectors, flywheel? Reason I ask is there is a break I thought it was 96+ that a direct swap, but prior to 96 the 4.0 was a renix( at least 88- early 90) and there was a differance in allot of sensors along with locations. Also doesn't your 00 4.0 have ciol packs instead of a distributor?

Yes it does have a coil pack instead of a distributor. but what is werid is the distributor goes right in where the pack goes and it runs like it should for about 10-20 seconds than it starts to act up. and the fuel press climbs when it acts up?

and yes the sensor locations are the same except for this one for one of the gauges we had to relocate but that wouldnt cause it to run so weird.

Unplug the upstream O2 sensor and see if it smooths out the idle.

that is the one right below the exhaust manifold correct?

Yup. The connector should be right around the #6 intake runner.

okay i will try that thanks. and what if it stops acting up when I disconnect it? wont the check engine light pop on?

The check engine light will come on. If it starts to run normal plug the sensor back in while its running if it starts to run worse I would bet that the O2 sensor is stuck either rich or lean. This could be confirmed with a scan tool capable of live data.

If it doesn't change anything than we'll try plan B!

well I tried that and didnt change a thing. whats plan b? I hope its not my engine.