Running rough, black smoke

[jeepsouth]

1043405

Hi, I'm a new jeep owner and have a few problems with my 94 4.0l cherokee.

It starts first time, but runs rough at idle and low speeds and cuts out when running downhill or when stopping at lights, and produces lots of black smoke from the exhaust.

The check engine light comes on for a few seconds at startup but there are no local agents that could read the error code so I am on my own.

I have checked the air filter , the plugs (black) and the leads are new, apart from that I haven't a clue, any ideas would be greatly appreciated

[addsig]

 

[dingus]

1043412

it sounds like you're running EXTREMELY rich... my guess would be the oxygen sensor. try replacing that. if that doesn't solve it, perhaps your piston rings are allowing oil to escape up into the combustion chamber and burn off with the fuel.



how many miles do you have?[addsig]

 

[jeepsouth]

1043424

my jeep has only travelled 40,000km and isn't using any oil.

Where would I find the oxygen sensor and can you tell if they are faulty or do you just replace them

[addsig]

 

[dingus]

1043489

the sensor is located on the exhaust manifold downpipe. to check it, unplug it and smack a voltmeter positive terminal on it. then ground the negative. start the engine and check the readings. it should be between 0.1 and 1.0 volts. if it doesn't read that, it is faulty. regular scheduled routine maintenence suggests replacing it 82000 miles or 82 months, but things can go bad at any time. hope that helps... if you need more assistance, pick up a service manual from an autozone or pepboys or email me and i can go into more detail. [addsig]

 

[MudderChuck]

1043492

The advice from Dingus sounds good, he is probably right. A couple of other things to look at are the ERG valve and the injector rail pressure. If you´re gonna have a Jeep you´re going to have to have the book, shop manual, Chiltons or such. Have also seen a cracked exhaust manifold, fool the O2 sensor. The cracks are often on the bottom or covered with the heat sheilds and almost impossible to find. Need a mirror, a flashlight and a really cold morning helps to generate some vapor that can be seen. Cracked exhaust manifolds often show up after a muffler replacement, when somebody was a little to heavy handed (BFH) removing the old peices.[addsig]