2018 Hisun Strike 550 Backfires on deceleration

[y2kbmet]

I'M STILL GETTING BACKFIRE UPON DECELERATION: 2 days ago, Strike was very sluggish, wouldn't make it up a hill. It is EFI with under 200 hrs. Yesterday, I replaced the plug with same exact I took out (NGK-R DR8EA), as it was covered in black soot. I cleaned the MAF with MAF Sensor Cleaner - not sure if I ripped one of the 2 o'rings pullling it out of it it was like that but either way, when I put it back in, it was seriously tight so I don't think that's affecting anything. I cleaned some of the throttle body (without removing it and without touching the flap), with Throttle Body Cleaner - it was kind of dusty. I cleaned the air filter which I replaced just 3 months ago when I did the oil change. All connections seem to be good. I could not find any exhaust leak anywhere. It got dark on me but I took it for a spin last night after putting it all back together and it seems to have it's power back but it's still backfiring when I decelerate quickly. Anybody have a clue what's next or had this issue before? TIA.

[aefron88]

There's no MAF it's a MAP/intake air temp (pressure as opposed to flow) sensor. I would replace that torn up o-ring and lightly lube them with silicone grease (avoid regular petroleum based grease as it can cause the rubber to swell)

Since you've already replaced the plug and checked the air filter, have you ever checked the valve lash? I would start there. If the valve lash is in spec I would check the injector next, it may be partially plugged.

It's also possible you have a sensor feeding bad info into the ECU which would effect fuel mapping, like the sensor noted above, but aside from fixing the orings that will be harder to track down.

[y2kbmet]

15 hours ago, aefron88 said:

There's no MAF it's a MAP/intake air temp (pressure as opposed to flow) sensor. I would replace that torn up o-ring and lightly lube them with silicone grease (avoid regular petroleum based grease as it can cause the rubber to swell)

Since you've already replaced the plug and checked the air filter, have you ever checked the valve lash? I would start there. If the valve lash is in spec I would check the injector next, it may be partially plugged.

It's also possible you have a sensor feeding bad info into the ECU which would effect fuel mapping, like the sensor noted above, but aside from fixing the orings that will be harder to track down.

Thanks for the info! Just ordered the o'rings, new fuel injector and inline filter. Will check the valve lash and then put these in this weekend and see which one does the trick. Fingers crossed! Thx again!

[Savage3]

Decel pop is usually a result of unburnt fuel in chamber.

Your air fuel ratio is off

[Dan_Lockwood]

On 1/6/2023 at 6:20 PM, Savage3 said:

Decel pop is usually a result of unburnt fuel in chamber.

Your air fuel ratio is off

Or an air leak in the exhaust system.  But that would not create lost power and dirty spark plug.

[lincolnsq175]

Check your valve clearence i bet its off.

[y2kbmet]

On 2/5/2023 at 4:57 PM, lincolnsq175 said:

Check your valve clearence i bet its off.

I am going to do that but I'll have to look at how to as this is the first UTV I've owned. Bought it used and now wish I would have just spent the money on a new one. Anyway, here's where I'm at with this since I've been out of pocket for so long due to surgery on my arm.  I've changed the spark plug and it ran better but it's still doing it and running poorly. So, I went ahead and ordered an O-ring set to fix the MAP as recommended above and I've ordered a new fuel injector.  My arm should be recovered in about a week so that I can do the work. I'll do the MAP, Fuel Injector and then check the valve clearance and update everyone then. I wish this darn thing wasn't so hard to get into and work on. If you're not familiar with this model, it includes removal of both seats and the entire console - pain in the rear. Thanks a million for the advice. If you have any links or info on how to check the valve clearance, it'd be much appreciated! 

[Steve G.]

Also check the engine water temp sensor. It is also one that can cause rich fuel mixture if bad.

[y2kbmet]

Update with the final fix. New Spark Plug installed but it still backfired. New Fuel Injector and new MAP installed - Problem solved. Had to do both at the same time b/c the unit is so hard to get in to.  If I were a guessing man, since I was able to start it up and rev it after installing the fuel injector, that was more than likely the problem but I installed a new MAP anyway. The old fuel injector was pretty ugly / dirty.  Hope this helps and thanks to all who chimed in.