2003 Dakota 4x4 3.9. P1391 code and an O2 downstream short to power code. Both crank and cam sensor are new and motor fresh rebuilt. Sync is set as it should be. I get the p1391 code only when the motor is cold. Won't rev over 2500rpm pops and farts and bucks when you try to drive it. Let it come up to operating temp and it runs fine. I have noticed at higher rpms when passing on highway I sometimes get a multiple cylinder misfire. All is brand new so I'm leaning towards a wire issue. Any known bad areas to check out in the harness? Any ideas where to go next? This is getting frustrating. The truck does seem a little harder on gas and lacking power compared to my old worn out v6 I had. What to do next?

 

What brand crank sensor did you install? These trucks seriously dislike the aftermarket sensors in critical locations..... the cheaper the sensor, the more likely it is to give you issues.

 

Agree TOTALLY w HeyYou.

These trucks would do better w a working/tested used oem sensor than a brand new off brand sensor.
New oem is ideal of coarse.

 

The fueling goes from open loop to closed loop at some point relative to ECT. The fact that it won't run in open loop but will in closed loop is a little backwards from normal.

Fuel sync is set at +0 straight up?

When I had similar issues with my 3.9, it was a crank sensor issue. A slow/offbrand sensor will see the two 5 degree windows as one long 15 degree window.

 

I looked back in my pile of receipts from the engine rebuild and the sensor is in fact an aftermarket. The fuel sync was set with the old crank sensor before the first time the code was thrown. At that time the fuel sync was 0 - 2. My snap on scanner read from 0 to +2. After the first episode of it acting up I replaced the sensor. After reading the comments I put the scanner on and the fuel sync is reading 5 to 6. I'm hoping it's just a cheap sensor issue. I'm ordering the mopar sensor from rockauto since the dealership in my town is rediculusly priced. In a few days I hope the issue will be corrected. The cam sensor was also changed to a known good mopar sensor that was in the old truck that this one replaced