Back fire when giving it gas.
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New User
Joined: Apr 2009
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Back fire when giving it gas.
Need a little help,2002 f150 with 4.2 68,000 miles, had since new changed plugs and wires 4,000 miles ago now truck is back firing and running rough when you step on the gas... Throwing no codes any ideas where to start?
Lead Driver
Joined: Sep 2006
Posts: 7,907
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Test the TPS for open or rough resistance through it's rotation.
This sensor tells the PCM about how much fuel to meter through the injection by how far it rotates and how (fast) it rotates, to add extra fuel for acceleration.
The mass air meter, crank sensor and OX sensors all get into the final fuel calculation but the TPS is a key fast acting sensor.
Otherwise, backfire is usually a lean condition (lack of enough fuel) and could be from low fuel pressure, restricted fuel filter etc or a combination of the above that sets up a condition that can ignite fuel before the intake valve fully closes because the PCM "advances" the ignition as a result of a detected lean mix being very slow to burn.
Good luck.
This sensor tells the PCM about how much fuel to meter through the injection by how far it rotates and how (fast) it rotates, to add extra fuel for acceleration.
The mass air meter, crank sensor and OX sensors all get into the final fuel calculation but the TPS is a key fast acting sensor.
Otherwise, backfire is usually a lean condition (lack of enough fuel) and could be from low fuel pressure, restricted fuel filter etc or a combination of the above that sets up a condition that can ignite fuel before the intake valve fully closes because the PCM "advances" the ignition as a result of a detected lean mix being very slow to burn.
Good luck.
Posting Guru
Joined: Dec 2001
Posts: 2,017
Likes: 2
From: Southeast FLA
I learned the hard way, and mighty fast (two times) to not buy wires from auto-parts stores. I'm not sure if you have the problem, but even premium guaranteed sets of wires were crap compared to the Ford set i finally threw on. Check to make sure you don't have plug wires that are arcing spark to other wires.
