2012 RMK 800 low RPM miss

[sdsnocop]

Recently picked up a 2012 800 RMK 2000 miles. It has a studder or miss at 4500 rpms. I had the TPS sensor tested and replaced since it was bad. The miss is still there. Runs good at idle and over 5000 rpms. Runs out at 8150 rpms at 6000 feet and 8000 rpms at 9000 feet. Told by Polaris mechanic replacing injectors would fix the issue. Anyone else experience this issue and anyone have experience with injector service companies? I do notice the miss is less noticeable if I run the fuel chip on ethanol setting even though I only run 91 octane non ethanol.

 

[ditch1000]

I would start with a new fuel filter. The ethanol setting give it more fuel; if that helps, I’d say you have a plugged fuel filter. I‘ve always changed mine every year no matter how much or how little I use it.
Plugged fuel filters can lean it out and scuff up the pistons.

 

[sdsnocop]

I would start with a new fuel filter. The ethanol setting give it more fuel; if that helps, I’d say you have a plugged fuel filter. I‘ve always changed mine every year no matter how much or how little I use it.
Plugged fuel filters can lean it out and scuff up the pistons.

Thanks, I have the filter on order. I do not know the maintenance history of this sled. I am also considering removing and running carb cleaner through the injectors.

 

[BeartoothBaron]

I'd think bad injectors would hurt the idle too, but not sure on that. In eth mode, with a bad filter, it might get better or worse: since it's trying to use more fuel, it might run fine until you get into it, then fall on its face because the filter is only letting so much fuel through. Anyway, the Pros are known for needing fuel filters frequently. I'd probably replace it as a matter of course on a sled with unknown service history. On cleaning the injectors, hopefully there's a thread on how to DIY here. That's another known problem area; cleaning them can't be anything that complicated, but I'd want to make sure I'm cleaning them effectively, and that I'm not doing something that could damage them.

 

[sdsnocop]

Replaced the fuel filter today. The old one was not plugged but was more restricted than the new one. The sled has yellow injector harness with a blue ecu so I assume the injectors have been replaced and the ecu re-flashed. I did remove the injectors and ran carb cleaner through them by placing increasingly larger tubing on the carb cleaner straw until it fit over the injector inlet. I pressured up the tubing with the carb cleaner can and hooked jumper wires to the injector pins to pulse open the injector. I also back flushed the injectors. Spray pattern looked good. Ran the sled on the stand and could very slightly detect a hesitation at 4500rpms but hardly noticeable. I will have to test drive to see if the hesitation is mostly gone. Of course I dropped the fuel line retainer clip where I could not find it so I had to fabricate one out of a washer.

 

[ditch1000]

Tip the sled on its side and shake it; they will usually fall out by the can..

 

[ditch1000]

I just picked up a 2013 Pro Rmk 800 163 this past weekend for $3500 canadian.. The owner put a Wiseco fix kit in it after a burn down and he said the previous owner also put a fix kit in it; I thought it screams plugged fuel filter..
I had an extra filter sitting on a shelf that I took off my 2014 Assault and only had about 200 km on it and was like new, so I swapped it out tonight.
The old filter was the most plugged filter that I have seen; I’d say it was atleast 50% plugged..
Always a good thing to check on a used sled!!

 

[chort2177]

You just put a new belt on… Check the deflection, warm it up to the point it is giving you the issue, **** it off, remove the belt to see if the issue goes away. It could be deflection set to tight for the new belt

 

[sdsnocop]

Rode the sled Easter weekend. Started the day good. The studder/miss progressively got worse through the day. I did adjust the belt deflection right after buying the sled.

 

[sledfre@k76]

Check your spark plug caps. If they are black and sooty where it contacts the spark plug, replace them. I had an annoying low rpm miss, ended being the plug caps. When worn from vibration, they dont contact the plug terminal tight. Simple fix! Big gains!

 

[sdsnocop]

Check your spark plug caps. If they are black and sooty where it contacts the spark plug, replace them. I had an annoying low rpm miss, ended being the plug caps. When worn from vibration, they dont contact the plug terminal tight. Simple fix! Big gains!

Thanks, you are thinking the same as I am. Have new plugs coming (spares are wrong ones) and ordered a pair of used coils with wires.

 

[sdsnocop]

Replaced coils, plugs and plug caps. checked and cleaned all connectors, stator tested within specs, added TSS bypass plug, tested capacitor, replaced voltage regulator. problem still exists. I have a video of the sled running and the 4-5 thousand RPM miss but have not figured out how to post it.

 

[sledfre@k76]

Replaced coils, plugs and plug caps. checked and cleaned all connectors, stator tested within specs, added TSS bypass plug, tested capacitor, replaced voltage regulator. problem still exists. I have a video of the sled running and the 4-5 thousand RPM miss but have not figured out how to post it.

I reread your posts to see if you replaced the injectors. It does not look like you did. Did you check each injector resistance? Compare them, if readings are way different between them. Replace the injectors. I had injector problems when I first purchased my used 12 pro800. It would drop out under higher throttle openings, on ground or test stand. Later on (4000 miles) I had the plug cap worn issue.

 

[sledfre@k76]

I reread your posts to see if you replaced the injectors. It does not look like you did. Did you check each injector resistance? Compare them, if readings are way different between them. Replace the injectors. I had injector problems when I first purchased my used 12 pro800. It would drop out under higher throttle openings, on ground or test stand. Later on (4000 miles) I had the plug cap worn issue.

Injector ohm resistance spec. is 12 ohms.

 

[sdsnocop]

Thanks I will ohm the injectors. My next step was either to replace the injectors or the wiring harness.

 

[TRS]

Have you done a leak down test?
Checked ex valves and bellows?
How about reeds?

 

[sdsnocop]

Still chasing this dang low RPM miss. I bought a used set of injectors to see if it made a difference. The same miss was still there but sled started to run on 1 cylinder and flashing the engine light. I tried to ohm the injectors I initially removed but had a hard time getting a reading. I sent the injectors to a company that services injectors. He also had issues getting an ohm reading until he pushed some voltage through the injector. Found connection issues with the harness connector to the injector. He replaced the connectors, cleaned and tested the injectors. They tested good volume, spray pattern and read 12.1 ohms. replaced the injectors with the rebuilt set and back to running on both cylinders but still have the miss. Still have to check exhaust valves and reeds.

 

[sdsnocop]

Pulled and cleaned the exhaust valves tonight. They were not too bad and came out easy. Visual inspected bellows and did not see any tears however when I connect a hose to the exhaust valve assembly one will hold vacuum the other will not. Tested by mouth pressure. One has air bypassing the bellow. I assume they are to hold vacuum so I will replace bellows next.

 

[sdsnocop]

Replaced the exhaust valve bellow on the one side. Found that the bellow was not the issue I did not pay close enough attention to cleaning off the old gasket. Now both sides hold vacuum and I can detect the working exhaust valve as I pulse the line to the exhaust valve. Disassembled the reeds tonight. they look good with only very minor chipping on a few reeds. I have a set of Boysen Carbon Tech reeds to replace them while I have them apart. Checked for broken or cracked piston skirts. They look good. Unless the new reeds eliminate the miss which I highly doubt I may have to live with the miss. I have run out of possible fixes.

 

[Teth-Air]

The RPM that this is happening is very close to the opening of the exhaust valves and likely a fueling change based on the TPS. I know you changed it out and recalibrated but could someone have played with the throttle body balancing? If you can partially remove the airbox and open the throttle enough to put a screwdriver in one of the throttle boddies and release the throttle to trap the shaft of the screw driver. Now measure the other side to see if it is open the same amount, or close. It was a popular thing to increase the oil injection for those motors and if someone turned the wrong screw??, Also I had one, and heard of others that had voltage regulators melt down and they ran poorly first.