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.

 

sounds crazy I know, but allow it to idle in neutral for about 15-30 seconds before you move next time you start it after it's been sitting for a decent amount of time.. get back and post up what it does, and if the problem persists..

 

Does the Iac need time to set its points before taking off or does the fuel pump need the time to fully re pressurize the system? I dont remember having to wait on it before this problem. If it helps the truck sat at an auction for about a month before I got it back (Repo do to economic struggle) it just started since then.

 

you're zigging, I'm zagging so to speak here.. Sounds like you checked the usual suspects, and didn't find any issue..

the next major thing that could be causing this 'when cold', has nothing to do with the engine (per say, as all components are working in concert to get power to the road, right?)..

My first thought when reading your original post was water in the dist cap, I've seen tiny cracks allow moisture to infiltrate, which causes a hard start, and running like crap for a few minutes- but you said you swapped those.. the next thing I would consider would be an injector- but electronic gadgets are usually all or nothin', once they go that's it.. So I'm stepping away from that one for the time being..

The next thing I would look at is your tranny fluid level.. if it is an auto anyway.. Your symptoms sound similar to a torque converter draining while it sits, and it takes a little bit to refill when you get going..that's the reason I wanted to see if it happens after you idle in neutral for a few minutes.. How many miles on that rig?

 

Does the truck start running rough after a couple of minutes. If so then the problem may be your pre cat O2 sensor. It takes a few minutes for the sensor to heat up then its starts updating the PCM. The pre cat is the sensor that causes the PCM to adjust the fuel mixture. When you punch the throttle you get the O2 to register a richer mixture and things smooth out until the sensor cools down again. Just finished going through this on my truck. If you know anyone with a scan tool that reads live data you can monitor the the sensor readings. It should fluctuate between around 80 or 100 mv (millivolts) to maybe 600 or 800 mv. This switching between lean (low voltage) and rich (high voltage) allows your PCM to fine tune the fuel ratio. They aren't expensive but removing is always fun its tucked up next to the cat and transmission. People here will debate with what products to loosen the rusts hold on your sensor but in my humble opinion the best way is to soak it for a day or so repeatedly with whatever you choose. I've tried everything but this CRC Knocker loose can't find it around here. But I've used PB Blaster, CRC Freeze Off, Liquid Wrench, AeroKroil and heat for mine and other stuff. Anyway if you determine it needs to be changed I suggest soaking it like I said then cut off the top of the sensor get a 22mm 6 point socket and breaker bar it should come loose. The cable connector should be on top of the transmission take your old one to the parts store and check that the connector matches up. I got one that was keyed differently even though it was supposed to be a pre not a post cat sensor or you can get a universal sensor cheaper and change the connector. Haha damn that was long winded but I know how frustrated I was getting LOL... Good luck

 

I started the truck and let it run a bit before taking off. No difference but I never actually suspected the tranny because it is more of a severe misfire than a tranny problem. I also attempted to remove the pre cat sensor but can not break it with anything. Ill try soaking over night before I cut the section of pipe out. I got much higher temp reading on the exhaust pipe before the cat then i did after (the method was advised by a local muffler shop) so i think the cat is clogged or damaged. Ill post if this works but after some in depth research it seems this is a common issue to my symptom (the pre cat not functioning properly) Ram has 138k on original cat and 02. Thanks for the help so far. Ill be sure to post a resolve.

 

i thing ur in the right direction i would try messin with the cat

 

Thanks for all your advice guys. Pulled the cat and it was plugged right up. Welded in test pipe and new turbo thrush muffler and it sounds great for a 35 dollar fix. I also swapped my muffler bearings never would have thought they could go bad.

 

Damn maybe I should check my bearings too they do have over 100K on them!! Hmmmm while you are at it you might want to top off the headlight halogen fluid to be safe... Just sayin