I've been chasing a problem in my '99 5.9 Durango for a couple of months now. It developed an occasional misfire and when idling, would sometimes keep slowing down until it stalled. Check Engine light indicated the upstream 02 sensor. First I replaced that with a Bosch aftermarket one and when that didn't fix it, bought a genuine Mopar one--made no difference. Also replaced the aft one. Sent the PCM off to have it checked & repaired if necessary--report was that nothing was wrong with it. Thoroughly cleaned the throttle body & idle air valve--made no difference. Had battery & alternator output checked & cleaned terminals. Last weekend replaced the plugs, ignition wires, cap & rotor and throttle position sensor. Seems to run fine for twenty miles or so then miss comes back and gradually gets worse (at highway speeds). It still occasionally slows down and stalls if left to idle for several minutes. After several of these stalls, the CE light again accuses the new 02 sensor. I obviously haven't thought of something..what is it???

 

check the catalytic converter

 

What type of plugs did you use? Did you use OEM wires or aftermarket? I hear MSD 8.5 wires are equal or better than OEM. I'd go with OEM/dealer O2 sensors. Usually, el cheapo Champion copper core plugs gapped to .40 inches is what's recommended for the Ds.

 

Thanks for the tips, but the car passed colorado's tough emission testing easily just before the problem began, suggesting the cat is working. When thumped, it does not sound like stuff is loose inside. Wouldn't the aft 02 sensor pick up that it wasn't performing?

I used NGK platinum plugs gapped to .40 and good aftermarket cables. (NGK actually manufacturers Dodge's 02 sensors in their subsidiary, NTK) Since the problem is unchanged, I think that eliminates those as a cause. In fact, the truck runs better now with this tuneup, as expected, but the mystery miss and idle problem still occur after it has been driven some distance--not on short drives. I'm stumped! Please keep the ideas coming!

 

this is your problem(or at least part of it), these trucks dont like platinum plugs, they run best on copper core plugs, preferably the champions referenced on the underhood label and in the owners manual, if the shop guy trys to tell you that any other brand, or core type is equivalent he is WRONG, simply putting platinum plugs in these engines can cause all sorts of problems including misfires and poor idling,

summary: take out the crappy overpriced platinum plugs and put cheapo copper core champions in it gapped at .040 and get back to us.

 

+1

Replace those POS plugs and buy some cheap Champion Copper plugs. Gap them at .040