2012 RMK 800 low RPM miss

[sdsnocop]

Had the throttle body off today to replace reeds. Cleaned throttle body and did visual inspection. With throttles closed on idle stop the amount of light coming through the throttles looked equal. I did swap out the voltage regulator with no change. The cutting out/surge was present prior to changing out the TPS sensor.

 

[Teth-Air]

You also could have a bad connection at one of the harness connectors. All it could take is a bit more vibration at that rpm. Running out of ideas.

Question: does it do it unloaded at that RPM when there is no belt on it?

 

[sdsnocop]

I have tried so many things I do not remember if I tried it with the belt removed. I have thought about changing out the wiring harness. I did go through and disconnect all the connectors and spray them with electrical contact cleaner. Thanks everyone for all the tips and advise.

 

[r.c.rob]

What is the compression in each cylinder?

 

[sdsnocop]

125-128 at 3500 feet elevation

 

[mrc]

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.

Well hope it works out. The only things left are stator, wiring harness and ECU I think. Stator would be my next suspect, but it would be an odd failure mode.

Did you check the TPS? (Procure a good accurate volt meter, procedure is over on hard core sledder).

Good luck.

 

[sdsnocop]

Well hope it works out. The only things left are stator, wiring harness and ECU I think. Stator would be my next suspect, but it would be an odd failure mode.

Did you check the TPS? (Procure a good accurate volt meter, procedure is over on hard core sledder).

Good luck.

Thanks, I checked stator ohm readings and it met specs I had found. TPS was replaced with OEM by Polaris dealer. I watched the mechanic whom I personally know set it by digital wrench. I have set TPS with volt meter before but I was just leaving for a trip and did not have time to do it myself. Thought about replacing wire harness next but ECU would be much easier to replace.

 

[mrc]

Thanks, I checked stator ohm readings and it met specs I had found. TPS was replaced with OEM by Polaris dealer. I watched the mechanic whom I personally know set it by digital wrench. I have set TPS with volt meter before but I was just leaving for a trip and did not have time to do it myself. Thought about replacing wire harness next but ECU would be much easier to replace.

Just make sure it is flashed to match the injectors used.

Another thought just occurred to me.... gap between the magnets and the pickups off the flywheel. If someday you get a hankering to pull the mag side motor mount screws, loosen the PTO screws and tilt the motor up so you can remove the pull starter.. you can check without pulling the whole motor.

Mike

 

[sdsnocop]

Swapped out the ECU and wiring harness. Did not fix the issue. Ohm tested the stator again. Stator tested good based on my multimeter which only gives me 1 decimal place reading with the 200 ohm scale so I cannot get the exact accuracy I need. The miss is not noticeable with the belt removed and no load on the motor. Took the sled today to the Polaris dealer mechanic I know to see what he can figure out. He is going to recheck the TPS sensor and try a different one to see if it makes a difference. Otherwise he will test the stator and try swapping parts with a known running similar sled. Hate to give up on this but I have exhausted all my options.

 

[mrc]

Swapped out the ECU and wiring harness. Did not fix the issue. Ohm tested the stator again. Stator tested good based on my multimeter which only gives me 1 decimal place reading with the 200 ohm scale so I cannot get the exact accuracy I need. The miss is not noticeable with the belt removed and no load on the motor. Took the sled today to the Polaris dealer mechanic I know to see what he can figure out. He is going to recheck the TPS sensor and try a different one to see if it makes a difference. Otherwise he will test the stator and try swapping parts with a known running similar sled. Hate to give up on this but I have exhausted all my options.

When you watched him set the TPS the first time, did he set both the base position and idle position (set base by adjusting the TPS sensor with no throttle cable attached and butterflys fully shut), then put throttle on and adjust idle to spec.

After pulling engine and putting it back in last year I found the base TPS position was off. Not sure how... perhaps the TPS took a bump in the process. But it started throwing a DET signal occasionally and idle ran a bit high. Adjustment of base fixed both problems.

Let us know what they find when they find it.

Mike

 

[sdsnocop]

Talked to the Polaris mechanic I know working on the sled. He was able to reduce but completely eliminate the issue by adjusting the TPS beyond recommended specs. He now believes the issue lies somewhere in the tps, maf sensor and connection to ecu. He eliminated issues with clutching. stator and fuel. He is going to reflash the ecu and ohm the wiring harness. I gave him an extra harness to also test ohms. He did find some questionable splices in the harness I installed he resoldered.

 

[mrc]

Talked to the Polaris mechanic I know working on the sled. He was able to reduce but completely eliminate the issue by adjusting the TPS beyond recommended specs. He now believes the issue lies somewhere in the tps, maf sensor and connection to ecu. He eliminated issues with clutching. stator and fuel. He is going to reflash the ecu and ohm the wiring harness. I gave him an extra harness to also test ohms. He did find some questionable splices in the harness I installed he resoldered.

That TPS system is a bit delicate. Any corrosion on contacts can effect the settings. Glad that it appears the source of the problem has been narrowed down significantly.

Mike

 

[sdsnocop]

Polaris dealer mechanic is still struggling with this. Says this is the first sled with an issue he could not completely pinpoint within a day of testing and swapping parts. He did find some minor corrosion in the TPS plug and cleaned it. Tried another TPS. Did find an extra seal on the TPS throttle connection which did not solve the miss but made setting the idle more accurate. He did find one of the injector o rings did not slide completely into the bore but had doubt it was causing he problem but will fix. He checked the PTO crank seal and was last working on removing the flywheel to check the mag seal. The stator tested to spec. Still only charging me with base diagnosis fee even though he has worked on this sled for 3 days. He is determined to find the issue with this sled no matter what it takes. He has been in contact with Polaris industry techs with this issue. I now do not feel so bad not being able to figure this one out.

 

[sdsnocop]

Spoke with mechanic today. He has found the issue but not the solution yet. He can set the TPS base setting to .8 volts and it runs perfect. But at .8 the computer will not allow the idle to be set. Also if he unplugs the MAF sensor it runs perfect. Either setting the TPS at .8 or unplugging the MAF sensor adds fuel indicating a lean condition at that RPM range. He is going to order new injectors to try. If that does not work he will remove and place them back on the parts shelf. He has Polaris tech support involved to help figure out possible options.

 

[sdsnocop]

Problem has been fixed. Replacing the injectors with brand new OEM Polaris injectors fixed the problem. I previously tried a different used set of injectors with no change. I had the injectors from the sled sent in to be cleaned and tested. They ohm and flow tested to specs but still was causing the issue. I will get the sled out on the snow tomorrow for final check. This whole process has been a total pia but I am now completely confident in the condition of this sled since almost every mechanical and electrical component has been fully inspected and tested.

 

[mrc]

Well at least you have that... The "devil you know" sled. Completely tore down a 2011 switchback assault and built it back up for that very reason. I could have replaced the sled with a used one for what I put into it.... but then back to the no confidence level of a new used sled.

Glad you got it figured out. I'm still puzzling over the solution though.

Mike

 

[sdsnocop]

Still baffled that injectors were the issue since I tried a used set plus had the original sent off for service and testing. Did some riding of the sled over 5 days and it worked perfect. Charged 520 for parts (injectors, o-ring, solder pins, exhaust gasket), 495 labor (5 days of diagnosis and testing, resolder MAP pins, replace broken bolt on helix, injector replacement).