Expert: Roland Finston - 12/5/2011

Question
We have a 1996 chrysler town and country. We have been having a problem with the van running rough. It liked to die while we were driving down the road and while stopped if you did not have your foot on the gas. We replaced the coil pack again. This is twice now. It has new pluggs and wires. It died and would not even crank over. We finaly replaced the computer. It finaly started up. It ran smooth once. We shut it off and restarted it and then it started running so rough the whole van vibrates. Now after checking it with the obd 2 it is saying that the coil is not working for 3 cylinders and that the injectors are not working on those same 3 cylinders. Is the new computer bad or is there something else that may be the problem. He also checked the wiring and said he did not find any bad spots and that he has power going all the way through.

Answer
Hi Taryn,
The only part which I can identify which would cause half of the cylinders to be affected both as to spark and injection is the cam shaft position sensor. It may be that the tip of the sensor is not positioned closely enough to the surface of the cam sprocket and that wear on the cam shaft is causing enough free play as to cause the signal to be lost during half of the rotational angle. Do you know which of the 6 cylinders are not firing? That would also give us a clue. If it were 1/3/5 or 2/4/6 then that would argue against my theory. It then would have to be related to wiring or grounding of both plugs/injectors on one entire bank of cylinders and that seems unlikely as there is no common wire for the plugs and the injectors nor does their appear to be a common ground except the cylinder head itself and I can't imagine how that could happen. On the other hand, if the bad cylinders were in serial order that would support my theory about the cam position sensor's signal being defective for a reason yet to be determined, but about which I conjectured.
Let me know which cylinders aren't working. If the sensor is going to be removed and re-installed a new paper spacer should be put on its tip, the o-ring lubricated as well.
Roland