Pontiac Repair: Jerking/Lurching Van, crankshaft position sensor, montana minivan

Question
2000 pontiac montana minivan 3.4 V6-  The van has started jerking and lurching at 40 mph and gets worse at 70 mph.  We were told that it was the fuel pump, but we have changed it out and are still having the problem.  I have also changed out the fuel filter and the fuel relay switch.  The tacometer jumps all over when this happens.  It also, at times, stalls out.  When the veh is in park and idling, there are no problems.  Any information would be greatly appreciated!

Answer
Hi Jason:

well I would say that you either have a bad crankshaft position sensor or the harness between the sensor and the ignition module is bad. you can check the sensor whith an ohm meter cold it should be between say 800-1400 ohms. if it much lower or much higher it's one or the other. check the senor at the module. the plug is on the drivers side and it has a yellow and purple wires. I'm sure that is why it's running that way and the tach is jumping all over.
Good luck:}