Rough idle at start-up/smelly exhaust

Tiny
TRAVIS STOUT
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  • 2002 DODGE DAKOTA
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
I noticed black residue and water shooting from my exhaust pipe and at the same time feels like engine is misfiring. I am not sure where to start looking for the solution as the check engine light has not came on. The exhaust smells rich so I am thinking maybe regulator or throttle position sensor.
Thursday, June 30th, 2011 AT 12:20 AM

5 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Chrysler has almost no trouble with either part. Start by looking for a vacuum leak. The oxygen sensor will detect that unburned oxygen and the Engine Computer will command more fuel. No matter how much extra fuel enters the engine, there will always be that unburned oxygen being detected.

Also consider the MAP sensor as a possible cause of running rich. He has the biggest say in how much fuel enters the engine. It can report the wrong value of engine vacuum but as long as those values remain within specs, no diagnostic fault code will be set.
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Thursday, June 30th, 2011 AT 12:50 AM
Tiny
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My parts store doesn't show a MAP sensor for this engine (much to their surprise also) I wonder if I also have a faulty check engine light because of the sheer amount of residue and water coming from my exhaust is such that when I am parked in my driveway and I hold it on 3500 RPM'S for 30 seconds you could write your name in the black spot on the driveway, thus making it hard to believe that the o2 and fuel are still within specs. If it doesn't have a MAP sensor what else would it have?
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Thursday, June 30th, 2011 AT 5:26 PM
Tiny
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The MAP sensor is bolted to the side of the throttle body.

Black soot from the tail pipe is not uncommon, and clear water is a byproduct of the catalytic converter doing its job, so those are probably not the best symptoms to look at. I'd be more concerned with feeling a misfire. The next step would be to connect a scanner that can read live sensor data during a test drive. If the oxygen sensors are switching rapidly between rich and lean a couple of times per second, the engine is most likely running properly. If one of the readings stays lean longer than normal, that O2 sensor is detecting the unburned oxygen from the misfire. You will smell the unburned fuel at the tail pipe.
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+1
Thursday, June 30th, 2011 AT 6:32 PM
Tiny
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I don't have a scanner or code reader so I guess this is officially over my head. About the MAP sensor: if O'Reilly and Auto Zone both don't show one for this engine does that mean that the entire throttle body would need to be replaced?
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Thursday, June 30th, 2011 AT 9:01 PM
Tiny
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Nope. Check it out on rockauto. Com
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Friday, July 1st, 2011 AT 2:20 AM

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