Hello dodgeforum folks, l go by Ron. I have an 01 ram 1500 4x4 5.2l (140k). Have had the truck 15yrs. Not long after purchase, I did a cold air, reprogram and dueled it. I had hi-flo cats to put in, but the exhaust guy talked me out of it, stupid! He puts the 2 o2s 12" away from eachother in the same pipe, even more stupid! My fault too, i should have said no. I knew the pcm would not like it. So jump forward to now. I started getting a misfire when i was going to work. When i get home I scan and get 2 codes.
1- p0305 (cylinder #5 misfire detected)
2-p1940 that's because of the incorrect exhaust work
After work I stop and get a plug and install it. Next morning same thing. I decide to get rid of this o2 issue so while i'm getting all new plugs(champion #rc12lc4), l get a bung plug for the ego and place a rubber sleeve over the o2(to protect and have fresh air) and tied up out of the way. Next day, same misfire issue, but over about 10 min it smoothed and stopped. After work, maybe 2 min then stopped. Great thing is I don't have the o2 issue anymore, but still have the #5 misfire. The colder the truck the longer the misfire. The misfire is undetectable if it's there until I put it in gear and give it gas.
The old plugs looked used, but not terrible. The new (fouled #5) plug still looks brand new (no oil and no excessive gas smell). Also checked pcv system, ok. Update for later today. Pulled k/n intake system and found only mild oil film in the pellum which for the truck's age and a wet filter system they used doesn't surprise me, especially since the "fouled" plugs are clean. So though the pellum could still be the problem, it doesn't seem likely w/no visible oil pooling, a clean plug and only 1 cylinder misfiring. Also disconnected #5 injector plug to see what happened and immediately got a p0205 (injector circuit malfunction - cylinder #5) so i'm questionable about an injector problem since i have never had this code and it started rough idling immediately and went back to normal after reconnecting injector and code reset.

 

I am finding conflicting information on the P1940.... it's either an injector circuit malfunction, or, and EGR solenoid problem. Considering your truck doesn't HAVE an EGR valve....... I wonder if that is a false code??? If you clear codes, does it come back?

Your truck has two O2 sensors. The pre-cat sensor monitor fuel/air mixture ratio. This one has the biggest effect on fuel economy, and how well the engine runs. The second sensor is supposed to be post-cat, and it just measures catalyst efficiency. Having them both in the same pipe is standard. (unless you have california emissions, then you might have as many as four sensors.....)

How is your distributor cap? Plug wires? May also want to consider a compression test......

 

HeyYou, thanks for your input. Reguarding the 1900 series code #, it's been several days since I reset that so I'm off on that #. It had something to do w/that 2nd o2 seeing the same dirty air because the fix I described is working and not giving a fault code anymore. I'm glad I finally killed that monkey.
Regarding cap and wires, I have been holding on that because I did a cap & rotor 1yr ago and the hi-po wires looked great. I did the arcing check last night in the dark and no light show. Early this morning while cold, I took a possibly good spark plug and put it on the #5 wire and no spark w/o reving. Same plug on different wire and great spark. I removed the wire from the cap and found corrosion. I used dielectric grease on both ends in the beginning and when I redid the cap a yr ago. Somehow moisture got in there and corroded the connection anyway. I cleaned the cap pole and installed the original mopar #5 wire (I kept the mopar oem's) and viola, no more misfire. I will be doing a cap, rotor and wires next weekend and will update the thread w/the outcome.
Thanks again for your input, HeyYou.
Job well done!

 

Let us know how it turns out.