If you have to ask how to replace it, you might want to leave it to a professional unless you have the time and are interested in learning car repair. This can get a little involved for the do-it-yourselfer although it is not terribly difficult.
To diagnose it, you can check the ignition timing with a timing light. If the marks bounce around a lot at idle, suspect the chain. You might also hear it slapping against the metal cover. A more accurate but more difficult method is to remove the distributor cap, then use a ratchet and socket to turn the crankshaft a small amount each way. The rotor in the distributor should start to turn as soon as you turn the crankshaft. If there is a delay when you change directions, the chain is loose.
Also be aware that there was a lot of trouble with distributors in the 3.9L in the Dakotas in the late '80s. The bushings would wear which allowed the shaft to wobble and change timing. That looked the same with a timing light as a sloppy timing chain.
A former student recently told me there is a modification to the timing chain that includes some type of tensioner to take up the slack that develops. They never needed that for the past 40 years so I don't know what changed, but you might inquire at the dealership about an upgrade kit. That would not be covered under any kind of a recall unless it's related to an emissions problem. Even then it might not be covered if it's considered normal wear. There would be a service bulletin that explains the testing and replacement procedures.
Sunday, May 1st, 2011 AT 2:00 AM