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roybelding
roybelding, ASE Certified Technician
Category: Mercury
Satisfied Customers: 4639
Experience:  35 years of retail operations on all vehicles
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Mercury Mountaineer 4x4: P0171P0300P0301P0304I'm fairly

Customer Question

P0171
P0300
P0301
P0304
I'm fairly sure I've had 0301 and 0304 before just not together, replace plug works fine for a while, if I remember right the plugs don't look burned or anything, fairly sure I replaced all O2 sensors, is there something I am missing, I've tried replacing the coil pack but the plug was the fix every time, is there something else I could check?
Submitted: 1 year ago.
Category: Mercury
Expert:  roybelding replied 1 year ago.
good morning my name is ***** ***** I will assist
the 171 is a lean code for bank 1 or the passenger side of the motor. it is set when the long term tims are too high, not because the O2 sensor is bad. it could be a vacuum leak along that side of the motor, pcv system, mass air flow sensor or low fuel pressure.
the 301, 304 codes are miss fire codes. usually plugs, wires or coil. if you have not done, I would replace the coil. you said you tired but did you actually replace it???
the 300 is set whn more than 1 cylinder has set a code for missfire. the common denominator here is fuel pressure. low fuel pressure will cause the miss fire codes as well as the 171 or lean code. I would rent a tester from a parts store and see if the fuel pressure is exactly correct.
Roy

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