i HAVE A 2001 RAM 1500 4X4 5.2 ENG. It runs rough and undrivable when it goes into closed loop. the long term fuel trims are +30 the upstream o2 sensor seams ok goes between .16 V & .98 down stream reads rich around .850 so what would cause the pcm to think the engine is running lean and increase the fuel trim while the upstream 02 is seemingly ok but the downstream is seemingly rich. the only code is cam/crank sensor code p1391 Cam and crank sensor has been replaced by my mechanic who is usually really good, he said he tested all the relevant wires and had the ecm tested and reflashed he had recently replaced the dist cap, rotor plugs . He tested the fuel pressure when it was running bad it had good pressure reading, the pump is only a year old. He has given up on the truck and I would like some guidance before I try something else.

 

in open loop the pcm is ignoring 02 sensor data. at this time the pcm is metering fuel trim based on preset calculations of engine rpm, coolant temp, iat and throttle position.
downstream 02 are not used in fuel metering at any time.

unplug the front 02 sensor connectors...if it runs good, replace the front 02 sensors.

 

Ok thanks, for what it's worth, I drove it this morning and the LT fuel trims were normal, near 0 and even after the fuel sys went into closed loop it ran great until the truck was up to operating temp, around 180 then the LTFT #s went nuts, +35 and the trk started to run terrible, it went back into Open loop and continued to run bad, I didn't think the long term fuel trim change so quickly, it has me baffled, reading near 0 then it went neg briefly and then immediately high positive.

 

Thank you primem for your input. I unplugged the upstream sensor, but the Truck is still running very rough. fuel system now remains in open loop, the only code now is for the O2 heater circuit and the scanner shows the sensor volt reading pinned at 1.000V. The fuel trims are all pegged at 0 The down stream O2 sensor is oscillating between .020 V & .860. Could I have a bad Cat. Conv.? ALSO I NOTICED THE TIMING IS OFF, anywhere between 13.5 and 22 on the scan tool. would certainly seem like it could cause my truck to run like it does, but the truck run good before it warms up? All these issues, Probably why my mechanic gave up on it .

 

Learned bad behavior. Leave the front O2 sensor unhooked, reset the PCM. (disconnect the battery, turn on the headlights, count to ten, turn off headlights, reconnect battery) Go for a ride. If it is still running wonky, take a look at what the PCM thinks engine temp is.