Ranger is stuck running in open loop. It will start out in closed loop but quickly get to temp and go into open loop. I have tested all the sensors and have hooked up my scanner and checked all the data everything looks good. I even tried a different computer but still the same problem. When in closed loop all sensors and readings are normal. Goes into open loop and all the sudden short term and long term fuel trims go to zero and the o2 sensor shuts down from what I have read this is normal. The only thing is there is no load on the engine it's just idling in the garage. It runs like crap you can actually tell a huge difference when it goes into open loop it almost stalls and runs so rough its a wonder it stays running. Any ideas would be good.

 

You said you checked the o2 sensors with a scanner? They're voltage will be constant. usually open loop is an Emissions deal.

 

I found the problem it was the o2 sensor wasn't staying hot enough to keep the truck in closed loop. Everytime it went to idle the sensor would cool down and force open loop cause it thought the engine wasn't warmed up enough. You must have enough backpressure to make the sensor stay hot. I only had a glasspack muffler and about six feet of pipe. I found a cat I removed from my srt4 neon put that on and bingo problem solved. Now working on someway to install a muffler. I was just playing around today and welded up some pipe and made a stack that comes up thru the bed. It just doesn't look quite right though lol.

 

Lol. Its gotta be nice not having that bed floor there. all kinds of room.