Hey guys I'm new to the dodge forum. Picked up a 2003 Dodge Dakota single cab from my uncle with the 3.9L. It sat for 4 years in the front yard and cranked right up with a jump pack. The truck currently has 118,000 miles on it. Got it with 103,000 and is in great condition. I'm having a bit of a problem with it that I've been fighting for about 2,000 miles and would like to hear some advice from everyone else. I picked up a misfire on Cyl 1,3 and 5. Has a light stumble in idle and runs smooth under throttle then on the highway you can start to feel a stumble again. Naturally i felt to do a tune up so i did Plugs (gapped properly), Wires, Distributor cap/rotor, Distributor pickup coil and also a crank position sensor. Still had the misfire. Also from a while back like 5,000 miles before this the truck did break down but the coil went out so its also relatively new. Fired up and still misfiring. The Pcv valve started to make a loud racket and i replaced that which fixed the light throttle stall it had problems with. Decided it was a good idea to check my 02 sensors the data looked good but the truck sat for a while so said why not and did the bank one sensor one 02. Still has the stumble. Compression is between 180-160 on all 6 cylinder. Fuel pressure sits around 55 psi at idle under throttle no change and nothing seems funky with the fuel trims. My buddy who had a 3.9 project gave me a known good ecm to try out and known good injectors still no change. I was nervous about the truck sitting for so long and did a complete seal overhaul on the engine and good thing i did because there was a ton of soot in the top end and in the pan. Heads did not have any cracks and valve seats showed no leaks. Cam looked good lifters had smooth actuation and looked good. Cleaned up the top end and the pan. I cleaned the piston surfaces up while i was in there as well. all put back together and still have a stumble but the engine sounds much better. I know it probably seems extreme to do all that but with it sitting for so long it eases my mind knowing the engine is in better health now. Most vacuum hoses have been replaced the ones that look suspect. i need to pull the 02 and try and run it without it possibly see if the catalytic converter is clogged. it doesn't seem to have any acceleration issues at all so i wouldn't think this would be the case. Will get around to that tomorrow and have an update then. Hoping if i get this figured out it could help someone else down the line doing their own wrenching. Curious what y'all think, Thanks again.

 

Since its all on one bank and spread across it I would lean towards a bad O2 sensor on that side or a large intake leak near those ports. Try unplugging the 02 sensors and see if it runs better. If so then you have your trouble spot. Keep in mind that dodge motors tend to be very picky with o2 and intake sensors. Try to go OEM or high quality aftermarket if they are unavailable.

 

Sorry for the late response. I unplugged the 02’s and it felt to idle better but I could still feel a miss. Drove it around a little had cylinder 1 and 5 throw a pending code but never triggered the CEL. I had my temp gun on me to see if one cat was getting hotter than the other and they seemed to be right around be the same temps 300-350F at idle. Manifolds at 450-500F. I’ve just replaced the intake manifold gasket for the second time, filling the corners with RTV to fill the gaps. I would like to think my intake manifold is good. I’ve put an upstream bank one Denso 02 in it. Thinking I’ll put a downstream in it as well considering the idle got slightly better