Pro 800 running on one cylinder

[DaFuzz]

I could use some help with my brothers sled, a new to him 2012 Pro RMK 800 155 with an intercooled Boondocker turbo running av gas that got towed to the trailer yesterday. We had a good morning, that sled was ripping hard all morning. When we came back out from a late lunch and started up the sleds that one was only running on one cylinder so we changed out plugs with new ones but it didn't help. I towed the sled back to the trailer and we started working on it today.

I did a compression test to start the diagnosis, both cylinders are 125-130 and within 3-5 lbs of each other. My first thought was that it might be an ignition coil, one of the other sleds on the trailer is a 2011 Pro RMK 800 155 that was running fine all day so we swapped coils with that, that didn't help the turbo sled still only runs on one cylinder. It doesn't clean up at higher rpms, just keeps running like crap and one side EGT stays at low when the good sides 350-400 degrees on Koso gauge. Using an IR temp gun the mag side of the cylinder head stays way cooler too so I think that's the problem cylinder. Pulled the plug and checked for spark by grounding the plug on a cylinder head bolt, both plug wires have very similar looking spark.

The sled will start and idle like crap with both plug wires connected, removing the mag side plug wire doesn't change the idle at all, still runs like crap. If I remove the clutch side plug wire the sled won't start or stay running at all, just dies right away. I put some starting fluid down the mag side spark plug hole and tried starting the sled with the clutch side plug wire disconnected, it doesn't even want to start.

I feel like I've checked for spark and fuel but EFI sleds are new to me and this is the first turbo sled I've ever touched so that's definitely new to me. Any pointers someone might have? Thanks in advance, I'm not sure if this should be in the turbo section or not but it doesn't seem like it since it doesn't seem like a turbo related issue to me

 

[boostboy]

Check the wiring harness to the injector, they are known to break and that is what happened to mine. The hardest part is that the plugs are glued to the injector and are difficult to get off. I soldered mine up and heat shrinked it up and it is perfect. I also had a wire break to the tps which was a little difficult to find. You cannot buy this harness from Polaris which is unfortunate but the injector ends are fairly common I think, luckily I had a spare one laying around.

 

[BILTIT]

Check reeds?

 

[DaFuzz]

Thanks for the tips at least it's some ideas that we haven't tried. I thought by putting starting fluid directly into the cylinder it would bypass the fuel and intake system? It won't even try to fire when I put ether in the bad cylinders spark plug hole and have the good side plug wire disconnected?

 

[BILTIT]

Please don't use ether!

If you want to bypass the fuel system just remove plugs, pour a capful of fuel into the plug hole, re-install plugs and fire it up.

 

[DaFuzz]

Will pouring a capful of avgas down the plug hole in the bad cylinder effectively bypass a reed issue or injector not working?

 

[BILTIT]

Injector yes, reeds no.

Sent from my SM-G925W8 using Tapatalk

 

[DaFuzz]

Ok cool, good to know thanks, stuff keeps pointing towards reeds, sounds like that's the next thing to check. What about a damaged piston skirt? is that still a possibility? Should the fuel in the plug hole run even if a skirts damaged?

 

[DaFuzz]

Thank you soooooo much for the help on this forum, got the sled all pulled apart and found both reeds in bad shape, one petal completely missing on the bad cylinder side but the good side was not sealing anywhere near well either. This might help us tune this dang sled a little better too since the reeds being in rough shape probably wasn't helping us learn turbo tuning.

Thanks to everybody that helped point us in the right direction!