hello ive got a 97 honda civic ex
So i've had this problem of my engine misfiring constantly when the tank gets a little below half. i go to a gas station, fill it up and the problem goes away. the engine code comes on as well but soon disappears after i fill it up. i have checked the code before it went off and it was the misfire code. sometimes on one or two cylinders or on all four.
I replaced the fuel pump when the stock one went out and did a tune up 2 years ago. the fuel filter was replaced 6 months ago and both oxygen sensors just over a month ago. i have a decent amount of experience as a mechanic but this one has me stumped.
thank you

 

Bad fuel pump, low fuel pressure? What codes are you getting? 300 is a multi misfire 301 302 303 and 304 are misfire on a particular cylinder. Check injectors, fuel pressure, coil, cap and rotor if you get any of these codes.

 

+1
Likely low fuel pressure possibly due to a weak fuel pump, clogged fuel pump sock filter, dirty gas tank, or maybe even water in the gas tank.

Try using some Seafoam or Lucas' Fuel Stabilizer in your gas tank and see if the condition improves.

 

Yeah I was just having the same problem with a code 300 303 and 304 all misfire codes. I changed my fuel filter and it has not happened since. I did also check my coil, plugs, wires and injectors while trouble shooting. To test injectors put a screw dirver on each injector one by one and put the screw driver to your ear at the same time. There will be a ticking if the injector is firing. To test coil and plugs see Honda Service Manual for specs. Did you use a Genuine Honda fuel pump?

 

You may find Ed Fisher's thread interesting and possibly relevant.

 

You should check your coil packs, some of these symptoms sound like a coil pack problem. It causes misfire and really badly might I add.
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Great Honda Civic Parts

 

Yea that definitely sounds like fuel pump issues

 

That would have nothing to do with it only happening with a half tank. Check your fuel pump/filter/tank, as everyone else said.