2017 Mountain Cat Surging/Low Idle

[North]

Back at it. I had fueling issues with this sled all of last season (stuck open injector, injectors grounding out due to wire chafe). This season it ran great twice until last wknd.

Took 5-6 pulls to start after parking it for a few hours to go ski. Usually holding throttle open helps. Not this time. Once started it pretty quickly started running poorly on ~3mi stretch of groomed trail. If I had it below 6000rpm it would randomly bog down (abruptly enough to throw my weight forward on the sled) Felt like riding with somebody who didn't know how to work a throttle. If i stopped it would quickly idle down and die. Started right up after 1-3 few pulls every time. It would stay running above 6000rpm but wasn't smooth. It starts right up 2nd pull, but idles around 1300 and sounds rough

Fuel system is where I started due to last year's issues. So far I've checked:
- Fuel pump pushes fuel when pull cord is pulled
- Fuel pump pushes steady stream of fuel with 12V connected
- Pulled Y-Pipe. Pistons look good. Oil is grey-ish brown. Not sure what it's supposed to look like.
- Ran without air temp sensor. This made things worse and dropped idle to 800rpm.
- All plugs have spark.
- I've cycled the injectors with 12V but haven't tried to start it since

Only other things I can think to try are get a fuel pressure reading and pull the assembly to check pickups, filter, etc.

 

[Old & slow]

Is your TSS connected or dis connected?

 

[spoon]

Greyish brown oil in cylinder is usually aluminum. Could be snow ingestion at one point that damaged a piston and that failure is starting to show. I had similar issue with my 2013 a while back. When sled was near new I loaned it to a friend and was told while he was riding it knocked the hood out of place as I had not used the lower mounting screws to make on hill access easier. It was a heavy pow day and I am sure it sucked in snow. He was a very aggressive rider as well. Fast forward a few years and I start having hot start issues. Going down a trail at mid throttle I start to hear rattling on chaincase side while moving. Stop sled and rattle goes away. Keeps doing this for a little while down trail and finally noise stops. On ride out sled isn't as snappy as before. Compression test back at shop and mag side is 10 lbs lower than the other. Pulled Y and found top of piston shows some damage, removed cylinder and intake (back) side piston skirt is completely missing. Everything else is fine. I put a new set of pistons in and has been good ever since, has been turbo'd for last 5 yrs.

Just saying check your base engine health, injector issue could have done engine damage previously.

 

[North]

Is your TSS connected or dis connected?

Disconnected

Greyish brown oil in cylinder is usually aluminum.

Just saying check your base engine health, injector issue could have done engine damage previously.

That doesn't sound good. In hindsight running it back to the truck above 6K rpm when it was surging was probably NOT the move. I've had the hood off of this thing so many times chasing that injector issue it's entirely possible it ingested snow at some point. I've had consistent hot start issues but hard to know the cause since that seems common for many. Sounds like it's time for a compression test. Thanks for the suggestion and explaining the thought process behind it.

Don't love the white film on the plug either (forget which one). Other plug photos are as follows MAG Front, MAG Rear, PTO Front, PTO Rear. Rears are not NOT carbon fouled, but swapping plugs hasn't noticably changed run state either.

 

[North]

Forgot to attach last one (PTO rear)

 

[North]

Compression is equal both sides. ~90psi @7100ft (phew!). Sled is starting and idling normally right now (of course, this thing is a master of deception). My gauge shows ~14.1-14.2V when idling. Only thing I noticed this time is spark looks orange to me, not bright blue. Of course these plugs have been fouled to some degree. They looked clean (but wet) this time. Never seen a totally dry plug come out of this sled. Only had two new plugs to try but when I swapped them in I couldn't see them firing? Old plugs went back in and have (orange) spark.

I'm leaning towards stator, because of how intermittent the issues are and since they're difficult to test. Could be a different electrical issue. Fuel pump (haven't tested pressure) and injectors still on the maybe list.

 

[Old & slow]

To me 90 seams low, I tested my old sled and lost about 20 psi compression form 2200 ft to 7800 ft. So if you lose 20 psi with elevation yours would be 110 with is still acceptable but on the low side. Now that could easily be the gauge or other factors. I don't think it would cause the runablity issues either as your problem is intermittent. If your stator is failing you should be able to ohm it and find out for sure. It may take some time but if you can ohm it when it's acting up that may confirm your stator is the culprit. Electrical can be hard to find sometimes. Good luck!

 

[North]

Yeah using common correction factors for altitude and 125-130psi for sea level compression I should be getting 100-105 at 7K. Cheapo O'Reillys rental gauge. On my old M7 my buddy's Snap On would always give me the numbers I wanted vs the rental gauges . The first gauge I used had a broken check valve...that had me sweating a bit.

I ohmed everything on the sled last season including coils, plugs, wires. Did some continuity checks too. Lighting coil tested out of spec and I don't have a value written down for Secondary Ignition Coil resistance - not sure why. Probably time to do it again as I've since replaced VR, fixed chafed injector wires, rerouted a pinched wire on the handlebar, swapped a coil that had damaged wires (pinched between gas tank and coil mount screw), and replaced a faulty tether.

I bought a bench tested stator to swap in. Will update if I ever get to the end of this mystery.