2000 Ford Focus mild surging

Tiny
YOGITECH1
  • MEMBER
  • 2000 FORD FOCUS
  • 4 CYL
  • FWD
  • MANUAL
  • 136,000 MILES
I have replaced the plugs, wires and coil. I have an engine light P0420 catalist below threashhold, was cleared and stayed gone for two days. Power is good when I take off but when holding the throttle steady it has an occasional surge like it is missing but no strong bucking. What else could be causing this issue? I have looked at the O2 readings and they seem to be W/I perameters so don't know what is triggering the code either.
Michael
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Thursday, March 12th, 2009 AT 12:28 PM

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Tiny
BLACKOP555
  • EXPERT
Were teh plugs and wires replaced for a reason?

That code means that the post convertor o2 sensor is malfunctioning, or the catalytic convertor has failed, which would make sense if you replaced the spark plugs and wires due to a problem that could have been pumping out raw fuel and burning up the convertor!

Also if the front o2 sensor(s) fail or missread it could cause the backone to throw a code as it is used as a refrence for the catalyst efficency.
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Thursday, March 12th, 2009 AT 2:42 PM
Tiny
YOGITECH1
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I replaced the plugs as I believe they were original and teh wires were leaking voltage, they had burn marks, I looked at the information last night again and although I couldn't get the info for the downstream O2 the upstream seemed to be all over the map form 70V to just under 800V with in m/sec. I believ this may be the problem as this appears to be eratic. Do you believe this would cause the fuel mixture to vary enough to cause the surging?
Just a little info on me I'm retired from the automotive field this issue just ocnfused me.
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Friday, March 13th, 2009 AT 6:34 AM
Tiny
BLACKOP555
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If its varying that much it could cause that problem, especially if its with it causing alot of fuel to be pumped in then hardly any at all.

What I would do is disconnect the o2 sensor and run it, if the problem goes away then suspect the o2 sensor or harness for the o2 sensor.

Does it run good when cold? In closed loop.
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Friday, March 13th, 2009 AT 2:22 PM
Tiny
YOGITECH1
  • MEMBER
Yea it runs this way when cold also, and I'll try running it w/o the o2 plugged in.
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Sunday, March 15th, 2009 AT 3:25 PM
Tiny
BLACKOP555
  • EXPERT
If it dont work with o2 sensor unhooked. Leave the sensor unhooked and remove teh battery for about 10 minutes, rehook battery and start, does it run?

Let me know what you find.
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Monday, March 16th, 2009 AT 2:19 PM

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