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2003 Mercury Marquis missfireing

Tiny
LARRY21201
  • MEMBER
  • 2003 MERCURY MARQUIS
  • V8
  • 2WD
  • AUTOMATIC
  • 91,000 MILES
I have put in new plugs, 8 new coils, a new computer, new fuel filter and this car still has a miss in it. At 50 to 55 on a open road if I com to a small hill it will spit and miss but if I gun it, it will take off and run strong. I need a machance not a parts changer help
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Sunday, December 20th, 2009 AT 4:37 PM

1 Reply

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Oxygen sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
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Sunday, December 20th, 2009 AT 5:14 PM

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