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Discussion Starter #1
For the last while I have been having backfiring issues with my quad. It's a 2012 550 arctic cat EFI. It's the second time it has happened. The first time a new air temp sensor fixed the problem. Now, about a year later it's doing it again. The mechanic tried a new air temp sensor and a new spark plug. Neither worked. He says it's probably the ecu that's the problem, and that it costs over $600. That seems rather high to me. Is that really the going rate for the ecu for my quad? Will I be able to find it on amazon or ebay? If so, what's the part number? And is there any other models that have the same ecu? Any other ideas as to the likelihood of it being the ecu? What do you figure the chances are of having got a faulty replacement air temp sensor? Thanks!
 

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Pretty rare for the ecu to be bad. Sounds like your mechanic is throwing parts at it without testing as per the specs ?
 

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Discussion Starter #3
What should he be testing? He's not an arctic cat dealer, but he's done lots of good work for us in the past. I would like it if it was something a little less pricey, although I know how it goes, quads really are a giant money pit, albeit fun!:) Something really makes me want to try another air temp sensor and see what happens. As cheap as they are, it might be worth it. The mechanic says it isn't, but I'm not sure I agree. It wouldn't be difficult to pop the suspect sensor into a different quad that it would fit in and see if that quad inherited the backfiring. What else would be a possible problem? Could the fuel pump not be working correctly? Clogged injector? Plugged fuel lines? Is there a fuel filter somewhere that can be cleaned?
 

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Download a free service manual at countrycat.com and look up troubleshooting.

Sent from my SM-G950W using Tapatalk
 

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Discussion Starter #5
I checked countrycat.com, and searched the manual, but nowhere did it mention backfiring in the troubleshooting sections. Oh, and one thing that I forgot to mention, is that the airbox is fine, so that isn't the issue. I'd be willing to try another air temp sensor or even an ecu if I could find it cheaper somewhere else, but just throwing $600+ at it in the hopes that it will help isn't very appealing.
 

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Check the intake boots for cracks , there is an updated clamp.
Is your battery in good condition, load tested?
 

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Discussion Starter #7
I think the battery is in good condition. It's about 2 years old and hasn't given me any problems. Starts great and all, so I doubt it's the problem. As to the intake boots, I'll have to check that, would a crack in it actually cause backfiring?
 

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Yes because it will run lean.
 

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I',m just throwing this out there too
at my hunting camp we have about a dozen atv's of different ages and makes.models
the guys that ONLY run NON ethanol fuel in them, NEVER get backfiring conditions
but ALL the guys that use ethanol in them get it now and then,

my personal atv started to back fire many yrs ago, and was my CDI (older model atv)
and cdi went after my buddy used my atv and forgot to shut it off, so idled for like 4+ hours before I found it??
and after that ran terrible, and tried many things, but ended up being CDI LOL

but I do see the other atv's backfiring due to the ethanol fuel use
so maybe try draining tank and using NON ethanol fuel and see if it helps before replacing a larger price tag item?
 

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Describe the backfiring. Is it all the time? only when you let off the throttle? exhaust or throttle body back fire. Are there any muffler mods? A battery going south can cause a back fire, other symptoms could be hard starting. Swap the battery with a newer one if you have access to one. how often does it back fire? An exhaust leak will cause backfiring. So would an intake leak as described above. These quads are designed to run on ethanol gas but non ethanol is better, by far. I dont believe its your problem but it's worth the effort to switch to non ethanol gas.
 

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Ethonol gas has absolutely nothing to do with it.. 13000km on one machine and 5000 on the other and 0 issues.. With the suggestions above also have the valves checked. The machine will sometimes start to backfire if the valves are getting to far out of adjustment
 

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Ethonol gas has absolutely nothing to do with it.. 13000km on one machine and 5000 on the other and 0 issues.. With the suggestions above also have the valves checked. The machine will sometimes start to backfire if the valves are getting to far out of adjustment
I will disagree with you, and I will say this as WHY< it sounds to me like you USE your atv OFTEN and as such your fuel goes thru it fast and its never really sitting with older ethanol fuel in it

and when used this way ethanol fuel is FINE< its why it works well in ON road vehicles that see's use often

BUT have anything sit long with ethanol and you start to see a LOT of issues with this fuel
talk to any small motor repair shop and ask then about ethanol fuel problems they see!
there are thousands of treads about issues with ethanol fuel that sits and or just the fuel some times itself
so I would NOT rule out fuel as MAYBE a possible issue/cause here!
again,. using fuel FAST most never see a issue with ethanol, so, your experience might be different than others!
 

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Discussion Starter #13
Sorry, I should have been more descriptive about what conditions it backfires under. It only backfires on deceleration. But one other thing that has happened occasionally with the quad, and there is no real rhyme or reason as to when it occurs, but I'm sure is related to the backfiring issue is that it will sputter a bit and lose power for a bit typically when under moderate acceleration at medium to low speeds, never at high speeds. But that sputtering doesn't happen every ride, just once in awhile, and like I said before, no rhyme or reason to it. It will happen when the quad has been recently started, and I'm just starting to accelerate for the first time, or it can happen when the engine is warm from a few hours of use or anywhere in between. And no, I have no exhaust mods, all stock. I had the valves adjusted last summer, so I don't think that's the issue? Might be worth trying though. The battery I'm quite sure is good. It starts just fine, no trouble there.
 

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Discussion Starter #14
And I have checked the air intake boots, both look fine to me, as to exhaust leak, how far up the system does the leak have to be to cause backfiring? Because the exhaust pipe leading from the engine to the muffler is not completely sealed, and hasn't been as long as I have owned this quad, so I have a hard time seeing that as the issue, unless you mean an exhaust leak inside the engine itself.
 

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Discussion Starter #15
Guys, thank you so much for all your help its been greatly appreciated! And I learned a big lesson today on exhaust leaks! Tiggershark, thank you very much for your exhaust leak suggestion! I was working on my quad a bit today to check the air intake boots and battery. Your suggestion got me to give the exhaust system a closer look and in so doing, I noticed that the two bolts that hold the exhaust pipe onto the block were a little loose, just enough to allow the pipe abit of movement. I tightened them up and took it for a spin, and the backfiring was gone! I could hardly believe it, so I loosened them off, and took another spin and the backfiring was back, so I tightened them up again and it went away again! I would never have believed such a simple thing could cause backfiring, but I sure do now! Thanks again guys for all your help! You saved me a LOT if time and frustration, as well as money!
 

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I will disagree with you, and I will say this as WHY< it sounds to me like you USE your atv OFTEN and as such your fuel goes thru it fast and its never really sitting with older ethanol fuel in it

and when used this way ethanol fuel is FINE< its why it works well in ON road vehicles that see's use often

BUT have anything sit long with ethanol and you start to see a LOT of issues with this fuel
talk to any small motor repair shop and ask then about ethanol fuel problems they see!
there are thousands of treads about issues with ethanol fuel that sits and or just the fuel some times itself
so I would NOT rule out fuel as MAYBE a possible issue/cause here!
again,. using fuel FAST most never see a issue with ethanol, so, your experience might be different than others!
Agreed!
 

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Happy to assist you. Now there are other symptoms involved with what you described as well. My 09 700 efi would backfire and bog-run crappy and the problem was a bad battery. Battery checked out good too. Plenty of starting CCA's power but it was on its way out. These efi machines are quite picky when it comes to batteries. Yours is 2 years old and keep it in mind if the quad acts up again. This is how it happened. Rode to a buddies house, about 1/2 mile away and it ran great. After an hour it started very hard as in crank and crank, backfired a few times and barely stayed running. Yeah , that fast it went south on me. Swapped the battery with one of my other quads and it ran great again. This is just an FYI as 2 years is about average for a battery. Now, the battery was still good enough to put in a carburetor ( non efi) quad and it lasted another 2 years w/o a single problem. So when members on this site suggest a battery, they know what their talking about. Anyway, happy to hear yours is fixed
 

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Happy to assist you. Now there are other symptoms involved with what you described as well. My 09 700 efi would backfire and bog-run crappy and the problem was a bad battery. Battery checked out good too. Plenty of starting CCA's power but it was on its way out. These efi machines are quite picky when it comes to batteries. Yours is 2 years old and keep it in mind if the quad acts up again. This is how it happened. Rode to a buddies house, about 1/2 mile away and it ran great. After an hour it started very hard as in crank and crank, backfired a few times and barely stayed running. Yeah , that fast it went south on me. Swapped the battery with one of my other quads and it ran great again. This is just an FYI as 2 years is about average for a battery. Now, the battery was still good enough to put in a carburetor ( non efi) quad and it lasted another 2 years w/o a single problem. So when members on this site suggest a battery, they know what their talking about. Anyway, happy to hear yours is fixed
Well, I just might need to replace my battery then, the sputtering and hesitating is still there, although backfiring is gone. It feels almost as if the fuel is sloshing and the pump is getting air(I say that to describe what it feels like, after what you said about the battery, I think you are right, I hadn't realized that efi machines were that picky about batteries). What you say about a poor battery makes a lot of sense, because at high rpms, there are no issues, so alternator is probably supplying the necessary voltage at those rpms, while at mid to low rpms the sputtering shows up, usually shortly after starting, I am beginning to find out, the issue disappears after 10-15 minutes of riding, so that all lines up with what you say about a battery on its way out.
 

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I was trying to log on 2 days ago to tell you to check the exhaust gasket. Mine started backfiring and I noticed the exhaust rattle. The gasket was shot. $12 later it sounds and runs great. I hope you have it running well now. Happy trails.
 

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I will disagree with you, and I will say this as WHY< it sounds to me like you USE your atv OFTEN and as such your fuel goes thru it fast and its never really sitting with older ethanol fuel in it

and when used this way ethanol fuel is FINE< its why it works well in ON road vehicles that see's use often

BUT have anything sit long with ethanol and you start to see a LOT of issues with this fuel
talk to any small motor repair shop and ask then about ethanol fuel problems they see!
there are thousands of treads about issues with ethanol fuel that sits and or just the fuel some times itself
so I would NOT rule out fuel as MAYBE a possible issue/cause here!
again,. using fuel FAST most never see a issue with ethanol, so, your experience might be different than others!
Guess we will just disagree on this one.. My machine now sits for 2 months out of the year since i stopped winter riding. 2 other machines have been sitting for almost 2 years and fired right up no issues both carb and efi.. My lawn equipment gets no maint and burred under the snow all winter fires right up every year on the second pull... Only time i have ever had fuel issues is the one and only year i used a fuel stabilizer in my fuel. wrong fuel stabilizer for ethanol based fuel and turned it to gel in everything it touched. Even my toyota truck that sat for 5 plus and fired right up...
 
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