I have a stock 1999 Jeep Cherokee Sport with the 4.0. I keep getting the P0340 code and the Jeep kinda jerks going down the road every once and a while.
I have replaced the crankshaft position sensor with new one from the dealership. Can't figure it out all and any help would be great.

 

That could could also be the Cam sensor inside the distributor.

 

Would that cause the jerking going down the road? Also could it be the ignition coil?

 

Yes and possibly. The code you are getting is specific to those two sensors though, I'd start there.

 

So I am still having trouble with my jeep. I still get the po340 code as well as p1391. I have checked both the crank sensor and cam or ignition pick up sensor and they test fine. I put a different computer in it and it still does the same thing. I have checked all my grounds and cleaned them. Jeep idles fine, no smoking from the exhaust. The battery gauge does go down to around 9 volts sometimes. Scratching my head on this one. Anyone have any ideas of where I should look next?

 

According to my FSM (2001) a weak battery can cause a PO340. what is the condition of the battery? Also, have you checked the condition of your sensor connectors and circuitry? I know you said you checked the grounds. Maybe hit the sensor connectors with some contact cleaner. The p1391 is an intermittent signal loss. If the sensors are good and the PCM is good. Chances are that you may have a problem in one of your harnesses. Keep us updated!

 

Have you tested the TPS at all? I'd look at that as well as the EGR valve, Idle-air control valve, clean the throttle body. How are your fuel injector wires?

 

Changed the TPS and cleaned the throttle body and no change. My battery tests good under load according to Oreilly's. Fuel injector wires are fine they were a little oily but I cleaned them as well as my connections to my ECM, Cam sensor, and crank sensor

 

I had same problem with my 2000, changed out crank position sensor, no help. found an fixed vac leak, problem solved. Don't know what the connection was, but jeep ran well after that.

 

Battery gauge should never dip to 9v. Have the alternator tested for free at az or advanced.
Also mine did that when a coolant hose leaked on it.

 

Alternator is less than 2 months old

 

That is what the guy that looked at it said it was. He said the alternator was bad and overcharging causing my problems. He replaced the alternator but still have the same issues

 

Had the alternator and battery tested and they tested ok. I am going to replace the battery temperature sensor to see if that changes anything. I tested the old one with a meter and it checked below the range so I will update what I find

 

Changed the battery temperature sensor and no change still over charging at the battery. Could it be a bad ecm or a damaged wire in the harness going from the alternator to the ecm?

 

Possibly. The voltage regulator is inside the PCM. I have no idea how to test it tho.