Ok I have a bit of a problem that just came up. 99 Ram 1500 3.9L

Yesterday morning I got in the truck and it was running bad. Misfiring, popping through the exhaust and idling real rough. After about 10-15 minutes it smoothed out and ran fine the rest of the day. So I immediately thought cap & rotor (even though I had replaced them both not more than 1 1/2 years ago). Yesterday evening I replaced both and asked the wife how the truck was doing and she said fine. I took it out for a drive afterwards and no problems at all. This morning I start the truck up and it is doing the exact same thing. Any ideas where to start looking next?

 

Sounds like it could be a moisture problem after sitting over night. When's the last time you replaced the wires?

 

The wires were replaced a little over a year ago. I may go ahead and replace those tonight.

 

Hey,

My truck had a similar issue last week. It was a bad pre-cat o2 sensor, for me. Put in a new one and the idle issues cleared right up.

While I was trolling around here for some answers, other folks had similar issues with clogged cats, blown 02 sensor fuse, often due to a blown intake plenum gasket. Some things worth checking anyways.

(i'm not an expert, just reporting what I found )

 

+1............

 

Ok. I replaced the pre-cat O2. No change. Complete tune-up (cap, rotor, wires, plugs). No change. Checked O2 Sensor fuse and its fine. I re-read the plenum thread again and I do have 1 of the symptoms at start-up until warm, fuel ping, along with overall poor performance. I did look down the TB, the best I could with the limited amount of space, and did not see any oil. I am going to do the test outlined in the plenum thread and see if this is the problem. I am almost praying this is the problem so I can move on with life.

 

Rough idle cold is going to be vacuum leak, (plenum certainly qualifies here....) or fuel pressure issue.

 

Hey everyone; I had the exact same problem last year. Turned out to be the collant temp sensor................Mike

 

Ordered the Hughes setup 3 day UPS so I can have it for the weekend. Will tackle this first thing Saturday morning and let you know how things turn out.

 

I may be crazy, but I don't think the o2's come online until you achieve a certain operating temperature.. I've watched it real time with a laptop slaved to the OBDII port, and when the engine starts to hover around 120*, it will start to sample o2's- on, off, on, off, on... and stay on after the engine starts to hold steady above 140*..

I'd rule o2's out if it's happening right at start-up.. the PCM is operating of pre-determined tables for operation at that point..

The NINJA HeyYou is on it... vacuum.. I trust what he says..

if that plenum gasket is blown, and you have a nice film into your intake runners from evaporated oil, and it is dripping into the cylinders themselves, that will play hell trying to get an engine warmed up... It would be fairly easy to spot, as you would get a nice puff of blue smoke a few seconds after start up.. and it would run like poo based on that.. and because your plenum gasket is in effect a vacuum leak too..

just my .02.. good luck dude!!!