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Discussion Starter #1
I've been dealing with this for a while and followed several great posts on this forum but have not figured out my issue yet. It always starts perfectly and idles fine but after riding a while, taking off from a dead stop with minimal throttle 3500 or 4k rpms, it will cut out, go, cut out, go and most of the time, WOT solves it for a short while. I can then back off the throttle and is fine for a short while until after a stop, then starts sputtering again.

Fuel pump pressure reads 41 right out of the pump.
Vent line is clear, tried opening the gas cap when it happens, no change
Have good spark although I cant measure while riding.
Voltage regulator tests good
Gas is good and fresh, I didn't take out the tank or anything just ensured it was fresh

I also have the high idle problem after hot, cant change gears because it grinds, but not sure if they are related. On that problem the belt looks perfect, and it looks like the butterfly is closing all the way.

Open to any and all things to check next or even repeat steps if I have to. Or of there is a good order to do things next.
 

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Fuel pump pressure is low. It should shoot up to 45 +- 2 lbs. Should shoot up there fast and repetitively. Easy to check under your seat. Sounds like your pump is going to me. Fuel filter on bottom of pump should be white if not spray it out with cleaner. If it is acting like it is starving for fuel it probably is. Rocky mountain ATV 190.00 Probably need one anyway.
Coils act like that also. Replaced my coil for 25.00. Mine would drop out a cylinder every so often at any rpm and it turned out to be a missing an oil pressure bipass spring of all things. The hydraulic lifters would not function properly at random times. Now with lots of new parts it runs very well. Polaris goes through lots of fuel pumps.
 

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Discussion Starter #3
Thanks! I ordered the hfp-396-u4f, about half the price and just replace the parts, not the entire assembly. Also comes with a higher PSI regulator which is supposed to solve the vapor locking issues in these things. We will see how it goes! Thanks for the info, I will report back once I get it installed.
 

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I don't know if the 2012 has a low oil pressure light. I believe my 2009 seized because the oil pressure bypass stuck open. The machine would sputter around 3500 RPM after it warmed up. I installed an oil pressure gauge to keep and eye on it. I think the fuel pump will be your issue. However, if not, and if you don't have a low oil pressure indicator of some sort, you could install a temporary pressure test gauge and watch it while running.
 

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Discussion Starter #5
I don't see a light for that on the round center gauge and I don't have any codes, or at least doing the key/button combo doesn't show any. Wish it had some kind of OBDII so we could get all those readings while driving to diagnose stuff like this! Maybe the new ones do, but my old 2012 does not. And its not really a 50" anymore either, did the super atv lift/wide kit with high clearance arms, clutch kit and run some take offs from a newer 1k. Until this fuel thing it has been an amazing machine especially for an 800cc still climbs hills, mud holes and trails no problems
 

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Discussion Starter #6
Well new pump went in and still happening. It seems to be worse but could be that I'm hyper focused on it. But sitting still in park trying to rev and sold steady ar 3k it Starts to die then comes back up, down, up down a small backfire or 2 even holding the pedal steady. Not sure what to try next and I have to go rent a fuel pressure tester to check the new pump.

On a good note the high idle when hot didn't happen today, not sure how the pump fixed that but not the spuddering assuming a lean condition.

Any more help is appreciated
 

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What year is your 800? Check and see if there is a heat shield on the passenger side. It should be bolted to the cross brace under your bed, it’s designed to deflect heat away from the fuel rail. Heat soak causes the fuel to boil in the rail and it will do exactly what you’re saying.

When it’s cutting out scroll through your speedo with the button, if you see ChkEng stop and hold the button and post the code you are getting. I’m assuming a 0 51 or a 0 52 which will indicate a misfire on either cylinder.

Check and clean the spark arrestor if you haven’t already.

Verify fuel pressure and idle and then have someone help verify at cruising speeds under a load. When you replaced the pump did you replace the assembly? If you just swapped out the pump from the housing there’s a chance you have a bad regulator or the O ring maybe but under the regulator
 

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Discussion Starter #9
Heat shield is there. Took bed off and ran it that way to help ensure there were no heat issues, but still doing the same thing. So here is what I've done and it's running good.
  • Replaced fuel pump and regulator and screen
  • Then It ran worse than before
  • I pulled the plugs and even though they give good spark they did look like the engine has been running lean. Rusty dry and the electrode seemed shorter than it should
  • So with fuel pump fixed and not enough spark it ran like crap above idle, started great and idled fine
  • Replaced plugs and ran better but didn't hold steady idle, up, down, up and down. Sometimes up around 2200rpm. but WOT was awesome!
  • Took off tps, looked clean, cleaned it anyway
  • Sprayed a bunch of cleaner thru the opening as well
  • Driving still cut in and out at 1/4 throttle or below 4k rpm. Anything above was great
  • Took off what I think was MAF and looked clean but sprayed it and thru the opening a lot
  • While I was at it I took off another thing that had a spring on it right above the TPS, but was dirty and gunked as hell
  • Cleaned it too and took for a ride and so far seems to run amazing at all RPM ranges
Looked like I had several problems compounded on each other but at least it only cost me the fuel pump and plug cost. Nothing terrible. Haven't been on a long ride yet but it did get hot enough to kick on the radiator fan and still seems good.

Thanks for all the help and suggestions!
 
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