skips,sputters, stalls at idle, sometimes

[AJ1500]

I need some help trying to figure out what is going on with my truck
a little history, it's a 98 4X4 with 5.9 and 200+K miles on it
it started about 2 years ago, just every so often it would begin sputtering and skipping if left at idle for a couple min. then it would die
then my cat converter came apart,I was getting codes for every cylinder misfiring at different times. I replaced the cat and the upstream 02 sensor
also replaced the exhaust due to being all rusted out, the truck had dual exhaust on it but every parts store I called said it came with single, so I converted it down to 2 into 1
now before all that the truck had got to where almost every time it would sit and idle it would go into the spit sputter then die issue, if I was quick I could hold the throttle and bring the idle up and most of the time it would be ok
but other times it would spit and backfire like crazy when taking off
I would have to work on and off the throttle and finally it would clear out enough to go, then run like a top until the next time. sometimes it will run all day and never do it. after replacing everything it seemed OK for a few days then slowly went back to doing it again.
I replaced the cam pickup in dist, tune up is fresh
now it's coding both 02 sensors, off and on. I can clear the code and it may run a few days before it sets the code again, the skipping doesn't really jive with the codes because the light can be on and it run like a top and never miss a beat, or the light will go out on it's own but the truck run like crap at idle again.

 

[Max78]

What brand O2 sensor did you use?

If you are getting a code for them I would look at the wiring first, then make sure you have zero leaks before the O2 sensor. If all else fails drop in some new NTK O2 sensors.

 

[dapepper9]

^^+1. NTK or direct from Dodge are best bet. Lotta guys wanna use Bosch because they're generally pretty good but not for these. Upstream will be only one causing issue, downstream is monitor only.

Another possibility is the idle air control motor. I fought hard starts when left to sit for 6hrs or more. It would start and stumble really bad. My issue was leaky injectors and iac in that regard.

Personally i would start with 02 being as you have questionable exhaust history on the truck and codes to match

 

[AJ1500]

I do have an exhaust leak that I am going to fix today, small leak at the flange of the right header where it meets the pipe from the cat. I can see that setting off the 02 sensor but don't understand how the sensor being coded for running rich can cause all the idle issues, and why is it so speratic
I have been leaning toward leaking injectors because my mileage also went to crap but don't want to invest in them until I'm more certain.
I did remove inspect and clean the IAC valve, it was a little grungy but not terrible
didn't make any difference
I just can't seem to wrap my head around why it will run like a top never miss a beat at idle then out of nowhere start skipping sputtering and die, or back fire like mad when you take off, then you have to kind of get on it to sort of blow it out, once you do it's back to smooth sailing

 

[yoda]

I would second replacing the upstream 02 with oe. It doesn't matter one these trucks if they stick rich or lean they will give that symptom on a cold start. It seems like the pcm always pulls fuel away when it is trying to test the 02 sensor operation.
If you have a scan tool, look at the long term adaptive memory when the truck is acting up, if it is -20% or more I would start with the upstream 02

 

[AJ1500]

OK I repaired the exhaust leak at the flange this morning
I checked and the codes were for #1 02 sensor high circuit and # 2 hi voltage
I had some injector codes but that was from me unplugging them when it was skipping to see if I could find one not working
I don't know if it fixed my problem but I can say it fired up and idled smoother than it has in a while. even when it ran fine it has had a slight rough idle when cold
so now all I can do is drive it and see what happens
the reader I have is just a basic reader and most of it's functions don't work
but it can read and clear codes

 

[Max78]

A leak before the upstream O2 can wreak havoc with your AFR and make an otherwise healthy engine sound like its on its last leg.

I had a Cherokee with a cracked exhaust manifold, it would not idle and ran like absolute crap, new exhaust manifold and O2 sensors and it was a new vehicle.

What happens is when the exhaust pulse passes the leaky area it draws in fresh air giving your O2 sensor a false reading of lean so the PCM dumps in more fuel to compensate, and well it can get bad enough to melt your CAT, and do all sorts of funky stuff.

Be sure to leave the battery disconnected for a good long while to reset the PCM for when you fixed the leak so your fuel trim tables can start from fresh, same if you install new O2 sensors.

 

[AJ1500]

define a good long while, I'll go unhook it now

And Thanks for all the helpful comments so far, this thing has been driving me crazy

 

[Max78]

I usually disconnect the positive cable for about 30 seconds and then I let the positive cable sit on the negative terminal and cable to drain the capacitors for about 5 mins.

If you simply disconnect it I would say let it set for 30 mins.

 

[AJ1500]

hmm never knew you could do that to drain caps, I will have to remember that
I unhooked the neg. for about 2 hours, should be good

 

[AJ1500]

OK now I'm really confused. now that the exhaust leak is fixed when I first start the truck cold it is smooth as glass, can barely tell it's running,,, but that only lasted about 3 min. as soon as the motor started warming up it started running like crap, but now it's all the time. it hasn't sputtered out and died or backfired and skipped after sitting at a red light but it is skipping non stop, I can feel it when driving just as bad as when it's at idle, it feels like it's trying to run on 3 cylinders and when I get on the throttle it takes it a min then it will finally kick in and take off but as soon as I let off it's back to skipping. so after about 30 miles all the sudden it started running so rich the exhaust was burning my nose and eyes. acting like the new cat I just installed is plugging up
or something, then the engine light came back on. I'll have to hook the reader up tomorrow again and see what code I get but WTH, I just fixed a small exhaust leak, that was it and now it is running worse than it ever has. it's never done this while driving down the road
I'm going to pull all the plugs and look at them as well
it has a brand new cap and button and new cam sensor in the cap not even 2 weeks old
what else should I look at, could the 02 sensor cause this

 

[dapepper9]

It definitely could. Unplug the electrical connector on the front 02 and test drive again. Take its signal out of the equation and look for a change.
Great explanation from the FlyinRyan tuning discussion page

 

[AJ1500]

so I got under the truck this morning before leaving for work and unplugged the 02 sensor, truck ran like a top, never missed a beat not one skip hick-up sputter or hesitation.
all I can say is Wow, and I'm amazed that all this time I have been fighting this problem it boils down to a small exhaust leak and now a bad 02 sensor. the sensor is new but I guess the exhaust leak caused it to fail.

now if I can just find the vacuum leak that is making my A/C vents change to defrost when I accelerate. or open the vents when everything is off during acceleration

 

[dapepper9]

Congrats! Now get er soaked in some pb blaster or kroil and get a new one in there

 

[AJ1500]

have the new one sitting here on my desk, gonna install it during lunch and unhook the battery for a bit.
I sure hope that's the end of this little adventure