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  • Engine bogs and backfires

    Hi all, I'm having some issues I can't figure out.

    1993 Festiva efi manual

    ​​​​​​It starts and idles fine. Drives normal for a minute or two and then starts bogging down and backfiring. If I shut it off for a few seconds and restart, it will drive normal for a few more minutes.

    Changed parts;
    Coil
    Distributor
    Cap and rotor
    Plugs and wires
    Fuel filter
    Has 52 psi fuel pressure

    Any ideas are greatly appreciated!!!

  • #2
    Backfires happen when the spark ignites fuel/air mixture at wrong time. Short delay suggests time for O2 sensor to warm up and start emissions control via computer. Absence of check engine light suggests sensor and actuator signals normal. So logically I'd look for loose hoses and drity sticking emissions components. Hope that helps narrow it down a bit.
    Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006.

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    • #3
      Awesome! I'll see what I can find. Thanks!

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      • #4
        Ok, I have check the pcv, all the the hoses and swapped the vaf. Still having the issue. What other things should I be looking at? This thing does a lot of off road so the cat is pretty beat up. Could the exhaust be causing this?
        Last edited by CoonsCars; 03-08-2019, 03:34 PM.

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        • #5
          Only shutting it off for a couple seconds will fix it? Sick your head under the car and look at the exhaust where it runs parralel to the fuel tank. Mine really got flattened there from off roading. Have you checked or adjusted ignition timing ever?

          Sent from my SM-G950W using Tapatalk

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          • #6
            Have you replaced (or unplugged) the o2 sensor? it sounds suspect to me also. It'll run fine just unplugged, though for the sake of fuel economy etc you may want to replace it if that turns out to be the problem.
            ~Nate

            the keeper of a wonderful lil car, Skeeter.

            Current cars:
            91L "Skeeter" 170k, Aspire brakes, G15, BP, Advancedynamics coil overs, etc. My first love.
            1990 Kawasaki Ninja 250 - my gas saver, 60+mpg - 40k
            2004 MotoGuzzi Breva - my "longer range" bike - 17k

            FOTY 2008 winner!

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            • #7
              The catalytic converter is an afterburner for removing unburnt fuel to meet emissions standards. If it has been ventiliated I guess that would lower the temp and it would not be as effective but I don't know if that would effect engine performance. A clogged exhaust sytem will show up on a vacuum guage or they say just to disconnect it and see the engine runs better which leads me to belive holes in the exhaust wouldn't be a performance problem. Someone may correct me on that.
              Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006.

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              • #8
                OK I unhooked the o2 sensor and the backfiring seemed to stop but it is still bogging in and our after warming up a bit. If I shut it off and then it back on, it will run smooth for a couple more minutes

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                • #9
                  Fixed!!! I took the ecu out of another festy and now it's doing great!

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                  • #10
                    Hurray!
                    Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006.

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                    • #11
                      Sweet!

                      Sent from my SM-G950W using Tapatalk

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                      • #12
                        Nooo!!!! False alarm, it's back. It drove great for about 2 hours of driving then it started cutting out. It never dies but it feels like it isn't getting enough fuel. If I shut it off and start it right back up, out ruins good for about 4 mins.

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                        • #13
                          Your list above doesn't include fuel pump. One thing to try is to open the hatch on top of the tank and inspect for dirt. I think you said you inspected the fuel lines or damage. However your experience with the new computer doesn't logically point to dirt in the tank or damage to the lines.
                          Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006.

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                          • #14
                            Ok I think I'm getting somewhere. When I swapped the ecu i was at the gas station and topped off. It only took about 4 gallons. Then I drove for awhile and it started happening again. I went and topped it off again and now it's back to running right.

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                            • #15
                              Originally posted by CoonsCars View Post
                              Ok I think I'm getting somewhere. When I swapped the ecu i was at the gas station and topped off. It only took about 4 gallons. Then I drove for awhile and it started happening again. I went and topped it off again and now it's back to running right.
                              The fuel pump has a sock on it for filtering that gets crusty. Those need to be replaced periodically. The fuel pump sits in a well that is filled with small holes. If those holes are plugged, the well only gets filled when the fuel tank is near full. This starves the fuel pump when the tank is 1/2 tank full and lower.


                              Sent from my iPhone using Tapatalk
                              "Fred" 93 Festiva L B6-ME Swap
                              “Though he is small, he is but fierce.”

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