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If you have a misfiring plug will your o2 sensors show rich or lean?

  • rich

    Votes: 9 64.3%

  • lean

    Votes: 5 35.7%
  • Total voters
    14
  • Poll closed .
blacksnapon

blacksnapon

Moderator
Staff member
9,461
301
waynesville,mo.
If you have a misfiring spark plug, will your o2 sensors show rich, or lean?
 
mrfixit

mrfixit

Chief Chaotic Engineer
8,334
171
Malfunction Junction, Fidelity MO -or- Mound City,
I voted lean. computers these days sense the misfire and turn off the injector, but the cylinder is still pumping air. 02 senser has a certain volume of air passing that would show lean because of the dead cylinder.
Even my old van ran pretty good with one plug wire off!
 
mrxlh

mrxlh

Oilfield Trash
5,904
430
Stigler, OK
Rich, still getting fuel, and not burning it. (unless the injector is disabled by the mis-fire code, which in that case it would lean it out) Depending on how loaded the engine is, it will also show detonation and a lower % level of free oxygen in the exhaust as read by the O2 sensor nearest the cat. So when do we get the answer Vince?
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
I voted lean due to the O2 being dumped into the exhaust from the misfire.
 
Fellro

Fellro

Moderator
Staff member
7,953
361
Iowa County, Iowa
I would say it depends, not enough info. If it is the fault of the plug/wire that it is misfiring, rich. If it is the fault of fuel supply or other issue, lean. Also, if the misfire is due to a mechanical problem, it can go lean or rich.
 
blacksnapon

blacksnapon

Moderator
Staff member
9,461
301
waynesville,mo.
OK, I kind of think this one is going as far as it will ever go! LEAN---the reason, O2 sensors measure oxygen, not fuel. Oxygen is consumed during combustion, no spark, no combustion, excess oxygen in the exhaust flow.
 
mrfixit

mrfixit

Chief Chaotic Engineer
8,334
171
Malfunction Junction, Fidelity MO -or- Mound City,
I think it will always read LEAN in rattlecan's truck; He's so broke he even makes the truck starve!
 
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