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I have a 96 civic non vtech. its got 143000. I have only been getting 300 miles to the tank which means like 25mpg. Im trying to figure out why the mpg sucks so bad. Im just now gonna change the plugs and wires (ngk vpower). I was wondering if theres any documented proven information on how much bad spark plugs will hurt your mpg? Or anyone know any real world info?

I cant imagine just a plug and wire changout giving me 50 more miles to the tank..........

 
Rep Power: 811

its possible. wires get degraded over time and you get less power to the plug. when the plug gets old, the gap gets bigger and requires more voltage from the ignition system. after a while, they will really strain the ignition parts to keep the engine running. when it gets serious, you will start getting misfires and rough engine operation. get some new ngk wires and plugs (copper v-power for $2 is fine, or get denso iridium if you have money to burn), new distributor cap and rotor, and check other little things like ground wires (check for loose connection or corrosion), loose alternator power wire, battery clamps, clean intake system parts like throttle body, IAC valve, fast idle valve (if equipped), change PCV valve (important!), change oil and air filter, get an alignment for the wheels, tire pressure around 30psi, remove excess weight from car, etc.

 
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ok the plugs i bought have the factory .044 set already. the plugs i pulled out u can see how the gap is expanded and they say .055.

 
Rep Power: 811

yup that would cause problems

 
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I got the plugs and wires in. so what about the cap and rotor? is that worth replacing? im thinking its over rated but idk.

 
Rep Power: 811

yeah you should do those too.