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Would a bad O2 sensor cause a misfire, rough idle, and power loss?

Discussion in 'Stock 1995 - 2001 Explorers' started by metal4life, December 23, 2011.

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    1. metal4life

      metal4life New Member

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      City, State:
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      Year and Model:
      1996 Ford Explorer Sport
      Hello everybody, I'm new to this site as I just bought an old '96 and need some advice/suggestions...she's got a ton of miles, and an engine rebuild is definitely in her future next summer, but for now, I have a few DTCs that stand in the way of a decently smooth running engine.

      When I bought it, it had 197,000 miles on the old OHV 4.0. But the previous owner DEFINITELY took care of it as the engine bay is spotless and mostly mechanically sound. Anyways, I was told it had failed emissions test and that codes P0133 and P0304 were responsible...ok...I drove it home and it definitely runs rough and noisy at highway RPM, and noticeably down on power(I think). It's also stalled a few times at lights when I'd slow down and disengage the clutch...

      I recently took it to Autozone to scan it myself as a project baseline so to speak, and suddenly the misfire code was gone, and it just said bank 1 was running lean....ok...I took it back today and plugged it in, and it just says that O2 sensor 1, bank 1 code again, nothing else.

      So I'm gonna pull that sensor anyway, but my question is, would a bad O2 sensor cause a misfire code? As well as that kind of effect on the engine? The prior owner said all the plugs and wires had been replaced to no effect...however she did mention that she happened to get some bad gas in it at one point, though I personally don't think it's related...

      Or is perhaps the misfire the true cause and the sensor was the first component to rat it out? Seems unlikely since the misfire code is gone now...

      I'm also going to try and clean/replace the MAF sensor as I've read it is a common cause of issues...but I'd love to get some expertise on this from someone who's had similar problems...
       
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    3. my98nnj

      my98nnj Well-Known Member

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      There's really no such animal as bad gas, more of a myth.
      The o2 issue will not cause a misfire, bad MPG yes.
      The lean issue could be an intake leak.
      When was the last tune up?

      The misfire could be either spark or fuel related.
      Injector failing, bad spark plug, wire, coil.
       
    4. 4X4RACER88

      4X4RACER88 New Member

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      your getting the o2 sensor code with the lean code becuase you have a vacuum leak. probably needs intake gaskets. its common on them and they are easy to replace
       
    5. metal4life

      metal4life New Member

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      When I get time, I'm gonna give it a once over myself, and plugs/wires are the first things I'm gonna check, then gonna test compression while I got the plugs out, test the coil/voltage, I really don't know much about fuel injectors and I'm not really tryin to tear into this motor till next summer when I have the money and warmer weather to sit outside n tinker...

      Another question, when I do go to rebuild it, is there a way to bump up the compression a little bit? I'm thinkin just maybe 9.5:1 to the stock 9:1...just as much as I can without causing big headaches...I'm probably going to get a chip, CAI, exhaust system, headers(maybe), and whatever other little improvements I can think of...
       
    6. metal4life

      metal4life New Member

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      So I replaced the O2 sensor yesterday, cleared the codes, then the P0304 misfire code came up again though it took 2 days of driving...however, this morning it wouldn't start, I don't believe there's any fuel in the engine. I took off the braided fuel supply line right next to injector #1 and the plastic intake runners and it was dry, I don't know if there's only pressure when it's running or what but after several attempts I couldn't get fuel to flow, or even smell it. Could a fuel system problem cause the misfire maybe? How can I test the pump?
       
    7. SoNic67

      SoNic67 Well-Known Member

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      With the key in "ON" position (even with engine not running) you should have full pressure on that line. Switch a few times between ON and OFF.
      Check the Fuel pump Cut-Off (passanger side by the kick panel).
      Check the fuel filter (driver side, on frame under door location).
       

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