Last weekend fired up the 2001 Dodge 5.9 liter w/140,000 miles and it started running so rough the truck was literally shaking all over the place. Thought maybe bad gas so I ran a tank of Lucas Oil fuel cleaner through it with no positive results.

Mid week CEL threw a P0306, #6 misfire code. In Feb I had relpaced the plenum with a Hughes kit, at the same time replaced the cap, rotor, plugs & wires. This week I pulled the the cap, rotor and # 6 plug and everything still looked great. I also looked onto the intake and with the new plemun it is dry as can be in there.

Since it still ran rough I swapped injector #6 with #2 to see it the problem followed. No codes since, but still runs rough.

Interesting thing is that there is still power, mileage hasn't dropped and after running down the Hwy it seems to smooth out (although not perfect) and sometimes it even purrs like a kitten. Although EVERY time I start it up cold it shakes and runs rough. I have also developed an exhaust leak at the joint behind the CAT. Not sure if it's related though.

After searching the forums hi and low I'm thinking a couple things. The Pre-cat O2 sensor is going bad, the CAT is getting plugged (not rattling yet), or even worse there is a crack between a couple valves on one of the heads.

Anyone have these symptoms and drove it to resolution? Can the O2 sensor be cleaned? If not at least that might be an easy replacement. Any way to tell if the CAT is bad for sure?

Thanks,
Mike

 

You should have replaced the o2(with an NTK from rock auto) and the cat (gut or replace with a MagnaFlow) when you fixed the plenum. Unscrew the precat o2 and see if it runs right.

 

Pardon my ignorance.... I just climbed under there and have a question. I thought the CAT was the oval unit after the pipes merge. What I see right after the header/exhaust connection is on each side of the trans is a small oval canister. On the top of the canister is one sensor and in the exhaust tube after the small ovals is another sensor.

What are the 2 canisters? Do I pull the ones that are screwed into the top of them?

 

Do you have a california emissions truck?

 

Check your ECT Sensor.

 

That's a cali rig, and those are pre cats.. curious thing is the big **** cat (the third one) is not monitored..

I doubt you clogged the pre cats.. they're pretty resilient.. if you did, God help you, they are stupid expensive.. You certainly could have clogged the big cat though.. you may wanna have a look see about that..

Are you saying it gets better when it gets to operating temp? Or, that its still missing? I hesitate to ask, but what color is your coil? If its yellow, take it off and throw it far far away.. it sounds like a really bad misdirected though, which could be caused by a legion of things.. check fire, check fuel. I'm thinking you can rule out air and exhaust, unless you have a vacuum leak..

Get a can of ether.. spray it carefully around the firewall, taking care not to hit the air intake.. if you hear a raise in engine speed, you have a vacuum leak, and you have a pretty good idea now where its takin up hiding..

Come back with results!

 

Misfire, not misdirected.. I hate this phone sometimes..

When you first start the engine, it runs off of a set tune that isn't based on environmental factors.. they are stored and don't change.. it immediately starts weighing variables afterward though, and begins adjusting.. the o2's don't come on line until the engine is somewhere around 120*..

Coil, straight up clogged cat, or vacuum leak is my notions.. did it all of the sudden start doing this or did it gradually get worse?

 

All 2001 5.9L came with 3 cats...2 pre cats and 1 large one after the y-pipe regardless of it being cali or federal emissions. My '01 RT is federal emissions and came stock with 3.

You may want to try removing and cleaning the throttle body, especially the IAC port on the back side and the tip of the IAC sensor being careful not to push or pull on the tip while cleaning or you could cause internal damage. If it doesn't clear up afterwards, you may need to replace the IAC sensor.

 

Yep, It's a Cali truck. The thing was running great and then out of no where I started it up at the ball field and it just started shaking. The roughness is worse on cold start. After running down the road it seems to smooth out a bit, but is still running rough at operating temp.

The coil is black.
I have already cleaned the TB really well.
I cleaned the IAC when I did the plenum and it still looks good.
No other misfire codes since I swapped the injectors, so the problem didn't follow.


I might try the ether trick first. That's probably the cheapest.
Then I'm thinking that since I was burning oil before the plenum fix and I have 140k miles that a new big cat may be in order. I have seen a lot of threads talking about the High Flow CATS. Any suggestions on brands and good place to purchase one?
If that doesn't do it I will look into O2 pre-sensors. I have heard about the NTK's from rockauto. Anyone have the correct part number?

Thanks,
MIke

 

be careful looking for cali rig o2 sensors.. that gets confusing quick.. go to NGK.com, and drill down using their database to find the part.. that's how I ended up doing it..

by the way: believe it or not, cali rigs make it a LOT easier to go duals.. the pre-cats are monitored, the big cat isn't.. you can cut the big one out (so long as your not IN cali, that is).. and run separate pipes.. I put a magna flow high flow on each bank post pre-cat, and run them to a magnaflow true x muffler.. night and day compared to stack.