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cat and o2 sensor

Discussion in 'Stock 1991 - 1994 Explorers' started by eric27, September 14, 2010.

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  1. eric27

    eric27 New Member

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    i bought my truckabout a year ago. recently i noticed a "patch" on my cat. im guessing that the insides are gone. my trucks semi loud. will that cause low mpg? also would a bad o2 cause 11 mpg? when my maf is connected i get black sooty smoke and the truck sounds like its under water, mpg goes to bout 8 mpg. unplugged i get the 11 mpg but drivability is way better.....yeah way better unplugged, sounds funny. need help
     
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  3. eric27

    eric27 New Member

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    well i guess ill sink more into this truck. itd be the best vehical ive owned if i could get the mpg up. muffler shop said 127$ for the cat and install. i guess its a drop in the bucket compared to the 1300$ invested so far....
     
  4. Maniak

    Maniak Moderator-Stock 91-94 Staff Member Moderator Elite Explorer

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    If your getting black smoke, your running lots of extra fuel there..

    That alone can/will kill a cat (melt and plug)...

    The most common reason for black smoke when running is a bad FPR. When it goes bad either the pressure goes way up or the diaphram leaks fuel into the vacuum line which is then pulled into the engine. Check the vacuum line to the Fuel Pressure Regulator.. If there is no fuel there, hook up a fuel pressure tester and see if your fuel is in the low 30's at idle and high 30's when the vacuum line is off.

    Also, running that rich can kill/spoil an o2 sensor too..

    Do you have a check engine light? If so, grab the codes..

    ~Mark
     
  5. Iron Weasel

    Iron Weasel Active Member

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    The catalytic converter doesn't play much of a part in reducing noise if the exhaust system is in good condition, that's what the muffler is for. Of course, if there is an exhaust leak anywhere in the system prior to the muffler then it will be louder. If you aren't in an area where safety / emission inspections are done, then it's entirely possible that someone gutted the converter rather than replacing it.

    The O2 sensor and MAF sensor are another matter. Either of those could cause the low MPG and driveability issues especially if they both happen to be bad at the same time.

    The MAF sensor sensor measures the total volume and mass of air flowing into the engine. This value is one of the major factors used by the Powertrain Control Module (PCM) in determining the fuel injection base pulse width and ignition timing advance. So if the MAF is bad or dirty, then it will be giving false readings to the PCM which in turn would cause the injectors to spray an incorrect amount of fuel into the cylinders. If the PCM thinks less air is coming in than really is, it'll dump less fuel into the cylinder and vice versa for more air.

    The oxygen sensor detects the presence of oxygen in the exhaust system and produces a variable voltage according to the amount of oxygen present. A rich fuel mixture will result in a low level of oxygen present in the exhaust whereas a lean fuel mixture will result in a high level of oxygen present in the exhaust.

    If the MAF is telling the PCM that there is a low air volume entering the engine, then the PCM will lean the mixture out, but then the O2 sensor tells the PCM that the exhaust is rich which is what causes codes to be set and the engine to run weird.

    Replace the catalytic converter then check for codes.
     
  6. eric27

    eric27 New Member

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    okay codes...998, 159. but the only parts thats are not brand new are the drivers side o2, and the ecc. .....i have tinkered with this truck since i got it....i had it running great for about a week, then it went bad again. i have bought new maf, iac, tps, ect, battery, fuel pump and intake lines, fpr, one o2, plugs, wires, coil pack,.....i think im beginning to forget some of them ...there are so many. thats why im not sure what my problems are from.
    some more intresting things.....it always reads cool, but feels hot after a min or 2? also only 6 volts on the connector side of iac??? is that normal? thanks for replys....i was starting to feel like it was a lost cause. but i love this truck!!!!!
     

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