1998 Dodge Dakota Distributor cap

  • 3.9L
  • 6 CYL
  • 2WD
  • 180,000 MILES
I had some rough idle like it was misfiring. Got a code for misfire on cylinders 2 and 5, I replaced the plugs, plug wires, rotor, and distributor cap. While I was tightening the distributor cap down, I noticed I could turn the cap some, about a quarter of a turn. So the distributor is bolted down, but the cast piece that the cap fastens to will rotate some. I had to get a friend to turn the engine over while I turned the cap to get it to run. It runs good now, but I get an odb-II code 1391 for the crank or cam position sensor intermittent signal loss. Why does my cap turn? I think it should be fastened down in some way to be in the correct position. I need some advice on this. Thanks very much.
Do you
have the same problem?
Sunday, November 9th, 2014 AT 4:24 PM

1 Reply

Are you saying the distributor housing is cracked into two pieces? I only saw that happen once before, a real long time ago, on a Volkswagen. Tying it down with a shoelace got the guy going again. That was in the mid '80s.

Chrysler had problems with their distributors in the early '90s where the bushings would wear out and allow the shaft to wobble. That allows the gap to change between the reluctor and pickup coil. That gap is pretty critical. At first it would cause erratic ignition timing, and if you could put up with the annoyance long enough, it would lead to a misfire each time that gap got too big to generate a sensor pulse. That problem was solved before they came out with the OBD2, (on-board diagnostics, version 2) emissions system on '96 models that would tell you which cylinder was misfiring, but the same thing could happen, I assume, with a cracked housing. If normal engine vibration made the pickup coil move too far away from the teeth on the reluctor, signal pulses would be lost intermittently.

The difference is you have a crankshaft position sensor for initial spark timing. The camshaft position sensor in the distributor is for injector synchronization only. That's why you don't notice much or any change in engine performance when you adjust the distributor. Spark timing must be very precise. Injector timing is not critical. What IS important though is you must have signals from both the camshaft and crankshaft position sensors for the Engine Computer to turn on the automatic shutdown, (ASD) relay. That relay sends current to the injectors, ignition coil, alternator field, oxygen sensor heaters, and fuel pump or pump relay. Loss of signal from the distributor will therefore cause a no-start condition or intermittent stalling.

Obviously you aren't supposed to be able to move the distributor cap around so we know you found the problem. In this case I wouldn't hesitate to find a used one in a salvage yard. The bushing problem was solved a long time ago, and other failures are very uncommon, so your chance of getting a defective one is real small.

By the way, I know you believe me, but code 1391 is:

P1391 - Intermittent Loss of CMP or CKP

"CMP" is "camshaft position sensor" which is in the distributor. This code proves you can believe the computer as much as you believe me!
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Monday, November 10th, 2014 AT 1:40 AM

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