I have a 2002 Ram 1500 4x4 with the 5.9. It has been idling rough and hesitates to the point of almost losing all power under load when cold. After punching the gas several times or babying the throtal over a 1/4 mile it seems to run fine until it sits about 8hrs and cools down then the same scenerio again. The gas mileage is around 11.2 not sure if that is normal for a magnum 5.9. I changed cap, rotor, plugs, wires (all oem replacement) iac (twice not sure about first one seemed like plunger was extended much further than 2nd one) tps (twice just for giggles). i cleaned the TB very well including where the iac sits and all vac ports. Checked the infamous pluenum no oil detected and no leak in intake (sprayed carb cleaner on outside) evap lines are good and charcoal box is not spitting any debry into lines. Im almost at a loss with this thing. Im still driving it daily. I have not yet tested pressure on fuel pump but Im not sure that is the problem i poked the needle on the test port and seemed to have plenty of pressure after warmed and cold (after sitting over night check valve seems to be holding). I also dismantled the fuel rail and all injectors and cleaned them very well. No codes stored. Please help it seems there are a lot of people with a similar problem and no one has come up with a solution................yet.

 

How old/how many miles on your O2 sensor? How about your cat?

 

Sounds like you have a sensor going bad, maybe coolant temp, ambiant air, map, or another sensor that affects air/fuel ratio. After your o2 sensors get hot and go to closed loop it clears up. I would run it by a shop that can monitor those sensors and verify they're reading correctly. Fuel pressure is a possibility even if you have some pressure at the test port. You should have around 55 psi (i think). Generally convertors and o2 sensors give trouble after driving, not on start up, but any thing is possible.

 

Thanks for your advice I pulled the cat and it was plugged up. Welded in test pipe and new cheapy thrush turbo muffler and it actually sounds pretty decent. I also checked the muffler bearings while I was there and all is well.

 

lol did you change out your o2 sensors.