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I bought a used 97 Mazda 323 BA 1.8L 16 Valve BP DOHC and the previous owner has no idea when the last time the fuel filter was changed ( he was pretty clueless about everything related to the car ).

There seems to be a bit of hesitation on acceleration and I was thinking of inspecting the fuel filter, but have no idea how to tell if it needs to be changed.

Even if the answer is, "you should probably change it just to be sure", I'd still like to know how to inspect it.

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Just replace it.

You're talking about a car from 1997. If you don't know when the fuel filter was replaced, I'm inclined to believe that it hasn't ever been changed. Very quick Googling shows me that a 323 fuel filter from that timeframe costs less than $20 USD.

If you really wanted to assure yourself that it's a problematic filter, you could disconnect the outgoing fuel line, place a catch can under the filter, turn the key to the accessory notch and measure the fuel that comes shooting out into the catch can against a known amount that the fuel pump is rate to pump over that time frame.

I wouldn't bother because:

  1. Fuel shooting out, hopefully going in the catch can, not catching fire and burning my garage down. No thanks.
  2. It's a reasonably cheap part that's usually replaced according to a maintenance schedule, not because it might / might not be sub-par.

Even if it turns out that it doesn't solve this particular problem, you'll have at least one part on your car that you know the exact history of.

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  • Great Pro Tip here, Bob. It just isn't worth it to really worry about it. Replace it and be done.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 25, 2015 at 23:06
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    I asked my dad this question years ago when I was broke, he said, "smash it open with a hammer and look inside." I just stared at him.
    – DucatiKiller
    Commented Feb 27, 2015 at 0:18
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    @DucatiKiller I have wish I could up vote that story multiple times. That's such a gem of Dad wisdom that sounds stupid and then you go, "oh, I see what you're saying." I'll have to use it on my boys when the time comes. ;-)
    – Bob Cross ♦
    Commented Feb 27, 2015 at 15:17
  • Ah good I was hoping someone would say "just replace it" haha
    – DJSpud
    Commented Feb 27, 2015 at 19:24
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Remove it and take a peak inside. If it's full of sludge, replace it. If you're a cowboy, blow into it and see how hard it is to force air out the other side. If it's working, you should see some fuel vapors coming out. You could theoretically clean and reuse the filter if you blow in the opposite direction, ejecting the blockages. Should save you some beer money until you're ready to install a new filter.

Pro tip: (Only) In an emergency you can poke a hole in the filter with something pointy.

If you've done all that and the car still hesitates, it may be time to have the battery, ignition (distributor or coilpack, as the case may be), spark plugs and fuel injectors checked. Everything save for the injectors is pretty easy and usually free to check.

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    If you are going to give a so called Pro tip: to "poke a hole in the filter" you might want to better describe exactly ... as you've stated, the uninitiated may just have fuel spilling out all over the ground creating themselves a very serious fire hazard. Personally, I wouldn't give this information in the first place, as most fuel filters today are self contained within a metal shell ... there is no way to "poke a hole" in the filter element. From my vantage, this isn't a pro tip, but very bad advice in the first place.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 23, 2015 at 15:24
  • It's a 97 model, ergo almost 20 years old. It has a plastic filter. If someone is stupid enough to poke holes anywhere else than the actual filter membrane, then I wash my hands of them.
    – Captain Kenpachi
    Commented Feb 23, 2015 at 15:44
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    Don't ever put your lips anywhere near fuel. Cancer is bad.
    – Bob Cross ♦
    Commented Feb 24, 2015 at 1:34
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    Incorrect. Gasoline is a cancer risk. The NIH has plenty of studies but this one is the most relevant to putting fuel in your mouth. ncbi.nlm.nih.gov/pmc/articles/PMC1128333
    – Bob Cross ♦
    Commented Feb 24, 2015 at 13:18
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    Incorrect again. That's not how the math works. Every time cells are exposed to a risk factor, they're at risk. Don't put fuel in your mouth.
    – Bob Cross ♦
    Commented Feb 24, 2015 at 15:53

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