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Why is my 91 Voyager 3.3 liter V6 tailpipe black with carbon?


27 replies to this topic

#21 jglen490

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Posted December 28, 2012 at 04:06 pm

Here's one explanation of the 51 code, from right here on good old Allpar:

 

  • 51 Oxygen sensor stuck at lean position (Bob Lincoln wrote: may be tripped by a bad MAP sensor system causing a rich condition, and the O2 sensor trying to compensate. The O2 sensor may still be good. The MAP assembly consists of two pieces, the valve and the vacuum transducer (round plastic unit with cylinder on top and both electrical and vacuum connections) - If you get hot rough idle and stalling, especially on deceleration, accompanied by flooded engine and difficulty restarting, that can be a bad MAP sensor causing the O2 sensor to try to compensate. If you get poor cold driveability, stumbling and bucking, and acceptable warm driving with poor gas mileage (a drop of 10 mpg or more), that is usually the O2 sensor. [Webmaster note: MAP sensors seem to die regularly.]

So basically, the computer is being told that the O2 sensor is STUCK and telling the computer that it (the sensor) is reading a lean condition in the fuel-air exhaust mix.  That means the O2 sensor is faulty.  It may be faulty because some other part has failed (i.e., MAP sensor), nonetheless it is faulty.  Replace it.  Trying to "clean" it will leave some residue on the reactive surface of the sensor, and it will send codes to the computer again.  Replace it.  You may also need to repair or repalce other parts; that will require more diagnosis, but a bad O2 sensor does have an immediate and irreconcilable negative impact on gas mileage, until it is replaced.

 

You will be amazed at the immediate improvement - been there a couple of times with my '92.



#22 fandini

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Posted December 30, 2012 at 01:18 am

picked up an o2 sensor today. You wouldn't believe how badly the one in the van was seized up. Got dark, cold and very widy here so I called it quits. Man am I becoming a wimp. Will try to get it taken care of tomorrow, but it's gonna be really cold. Thought about getting some MAF sensor cleaner and cleaning it up while I was at it. Oddly enough, the van runs spectacular. No cold starting or running issues of any kind hot or cold. SMMOOOOOOTTTHHH.



#23 ImperialCrown

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Posted December 30, 2012 at 07:11 am

 The PCM only uses information from the O2 sensor once it warms up and enters closed loop. When it is cold, the PCM relies on an internal program to determine mixture and advance.

 Get the exhaust pipes nice and warm before trying to unthread the O2 sensor. Avoid damaging the threads. A foaming graphite penetrant works nicely and anti-seize paste works well putting it together.

 Use an OEM O2 sensor as I've had problems with Bosch.


Edited by ImperialCrown, December 30, 2012 at 07:12 am.


#24 fandini

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Posted December 30, 2012 at 05:10 pm

Picked up an NTK sensor from NAPA. They said it was the brand the OEM called for. I've never heard of that brand before, heard of NGK but not NTK. I don't know. I hope it's a quality brand and a direct replacement. You guys ever heard of an NTK? Is that the brand you would use?



#25 ImperialCrown

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Posted December 30, 2012 at 05:19 pm

It would appear that NTK and NGK are the same company? You should be good.

 http://www.ngk.com.au/oxygen-sensors



#26 jglen490

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Posted January 2, 2013 at 03:46 pm

Just be careful with the anti-seize compound so it doesn't contaminate the sensor surface itself.



#27 fandini

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Posted January 2, 2013 at 03:55 pm

Been driving it a couple days now. Only have about 50 miles on the new O2 sensor and the code reset. Milage according to the overhead is back up to about 16 from the bowls of 10 to 11 mpg. We'll see if it doesn't set a code again. Oil is black from running rich so I will probably change it again after I'm sure the lean/rich condition is fixed. Thanks for your help.........AGAIN. Now I need to track down the smell of gas which is constantly around the vehicle and some other odds and ends. I'll have to start a new thread for that one. Thanks again.

#28 jglen490

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Posted January 4, 2013 at 05:09 pm

Happy to share experiences :thumbsup:




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