I recently upgraded to a 98 Dakota after my 93 was totaled. So far it has been a good upgrade but i have been having issues with the CEL coming on. It has a Re-manufactured PCM and has 208k miles on it
Im getting these codes:
P0300 Random Cylinder Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0305 Cylinder 5 Misfire Detected

As near as i can tell the engine is running perfectly fine about 99.99% of the time, but every once in a while i will feel a jolt from the motor while im driving down the freeway. the CEL usually comes on about 24hr after this jolt if it was cleared/read. ive had it read and cleared 3 times in the last week and it keeps coming back.

After some google searching it looks like Cylinder misfire codes are a common problem on bank 1 (cylinders 1,3, and 5) for ODBII 3.9L dakotas, but so far i havent been able to turn up a consistent answer as far as the cause.

What i have done already: New Cap/rotor and spark plugs

What i am planning to try next: Injector cleaner and an oil change with some seafoam, maybe new plug wires and coil

Possible causes ive read for this problem aside from cap/rotor/plugs:
Timing chain
bad injectors
bad Crank/cam sensors (usually accompanied by a CNK/CAM code however)
problem with canister purge solenoid
02 Sensors
intake/plenum gasket
head gasket/cracked head

I know the 3.9L magnums had a wear problem on the timing chain, i changed the one on my 93 because i could hear it rattling. i know that could cause this due to improper crank/cam sensor positions, but i don't hear any similar rattling from this motor.

So, most of those other threads ive looked at are several years old and never had much of a straight answer. so im wondering if anyone else has had this issue recently and how they fixed it.

thanks
-Nemesis

 

I think with those codes and the high miles on that engine,a few things id be checking for sure is..1) plenum gasket,im sure its leaking!its also a vaccum leak as well,check for oil build up in back of plenum..2)im sure your timing chain is a little stretched,so that will throw of your fuel sync(timing)might have to take it to shop to get that set,it requires a high dollar scan tool...3) check for a general vaccum leak,such as brake booster line and valve,check small lines as well...these can all cause random misfires...

 

I would swap your bank 2 upstream O2 with your bank 1. See if the codes follow to the passenger side cylinders.

I ran into this same problem and after replacing plugs, wires, cap and rotor it was the bank 1 sensor 1 O2.

 

My dad says the plenum gasket is definitely a troublemaker on these engines, so i will check that out. I think the chain may have already been replaced. if it hadnt im sure it would be rattling quite a bit with that many miles on it. the PCV valve on the right side of the motor isnt working properly but my dad says he doesnt see how that might affect it.

AFAIK on the 98 there are only 2 O2 sensors, upstream and downstream of the CAT, but i will look into that.

 

it depends on your emissions model. Some have 1 cat 2 O2 and some have 3 cat 4 O2

 

I have 2 cats, 2 O2's on each (4 total) - mine is a Canadian truck tho.

 

well i put some injector cleaner in it and some seafoam in the oil (going to change it next weekend) and so far the CEL has not come back on yet. rotated and got the tires all up to pressure today and ill go out to town later and keep watching it.