Yamaha sidewinder falls on face

Original poster says it does it on a full tank of fuel also.
 
Brett Allen said:
Nope no lights no codes, running straight 100ll av gas
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I have used AV gas in my sleds on and off over the years as well. I don't run AV gas in my SW or Attak as I am concerned about O2 sensor issues with the high Lead content of 100ll.
Aviation fuel has been discussed at length with varying opinions on its use in sleds.
I have never had much luck running pure AV gas in my sleds although my 1970 Mustang Mach 1 loved it.
I do know that my 1981 440 SRX mod did not run worth a darn on 100ll unless it was mixed with 91 octane at a ratio of 2 gallons of AV to 3 gallons of 91 premium.
Your issue could be simply a fuel issue so maybe try some actual high octane fuel designed for sleds or a can of Torco in 5 gallons of pump premium.
Worth a try.

Another thought is that the sled is running rich and gets worse as it builds heat...an AFR module/readout would really help diagnose the issue.
 
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Are you using a "wire" style air filter? Looks like it is collapsing during the long pull and making the prefilter getting sucked in. Is it making you "starve" for fresh cold air and heat soaking the turbo?
 
Brett Allen said:
I’ve got a 2018 sidewinder MTX, running precision 280 flash, hurricane performance secondary intercooler, external intake, race exhaust, rollover valve is dumped to tunnel exit, Tki belt drive, sting ray mods clutch kit with thunder products add ins. I’ve tried searching the mountain page but there isn’t much info or as many members, just looking to see if anyone here has experienced this.

sled falls on its face on longer hard pulls, never backfired or pops just like the ecu pulls power. Sled holds 8900-9000 rpm till it happens, doesn’t matter if it’s full of fuel or almost empty. Holds 19psi while in the throttle, all boost lines are tight and clean inside. I’ve sent the video to Precision and was told it wasn’t tuning related. I’ll add a link to the YouTube video of it. The file was too large to upload. It starts falling on its face 39seconds in and continues till I turn out.

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IMO, sounds like it just plain runs out of fuel.
I'm sure you know this but PEFI specifically states to NOT ever run a CAI on Stage 3 as the engine will go lean for sure.
Even though you're running 100LL, that doesn't mean it has enough fuel. It may not detonate but it still can run out of gas. IMO for SURE I'd put a fuel system upgrade (larger pump with return to basket if possible).
Also, recently on TY (and other sites) there is chatter about PEFI's knock protection not working. IDK if that has any bearing here but I'd certainly do a compression test and if possible, use a fiber optic camera to look inside each cylinder.
I just pulled my fuel tank apart and found debris in strainers (red plastic particles). Also, just had my fuel injectors ultrasonically cleaned and flowed and found some debris in 2 of 3 in inlet screens. Critical at your level of output that fuel system is up to the task.
Just my 2C.
 
Have you monitored your air intake temp. It’s one off the choices on the lower left on gauge. If your intercooler is plugged off with snow the IAT will get to a point that engine will cut out.
 
THEPASMAN said:
Have you monitored your air intake temp. It’s one off the choices on the lower left on gauge. If your intercooler is plugged off with snow the IAT will get to a point that engine will cut out.
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Yeah just did it on me again yesterday intake temp never went over 80 degrees, rpm was right at 8990 boost was 17psi, it instantly dropped to 10 psi
 
Brett Allen said:
Yeah just did it on me again yesterday intake temp never went over 80 degrees, rpm was right at 8990 boost was 17psi, it instantly dropped to 10 psi
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I would do a boost leak test if not already. It’s not enough to just check clamps.
 
At that level of boost for that long, IMO I think it's either out of fuel (as I previously questioned) or head/pistons get so hot, it goes into big-time deto and knock protection shuts it off. Ask me why I think this. Hint, I just finished rebuilding my engine.
 
I'm not convinced this is fuel related. OP states this is only with altitude. No problem running at lower elevations. This is lack of flow imo. Boost leak, exhaust leak or just a low flowing exhaust.
 
Thanks everyone for all the suggestions and things to check. It was the tune from precision.. the only change I made was a re flash from hurricane performance. Flashed their 270 high elevation tune. Went back to the same pull, it was same conditions as the last climb but about 5 degrees warmer out. Sled pulls harder off the line, and pulls like a freight train all the way out the top. No drop in rpm, no boost or timing pull backs, Boost never dropped below 17psi while holding it wide open, intake temps never went over 110, held 9050rpm all the way out. I had to add 2 grams of weight with the hurricane tune. I’m still going to do the fuel return relocate and throw the higher flow pump in for peace of mind.
 
Brett Allen said:
Thanks everyone for all the suggestions and things to check. It was the tune from precision.. the only change I made was a re flash from hurricane performance. Flashed their 270 high elevation tune. Went back to the same pull, it was same conditions as the last climb but about 5 degrees warmer out. Sled pulls harder off the line, and pulls like a freight train all the way out the top. No drop in rpm, no boost or timing pull backs, Boost never dropped below 17psi while holding it wide open, intake temps never went over 110, held 9050rpm all the way out. I had to add 2 grams of weight with the hurricane tune. I’m still going to do the fuel return relocate and throw the higher flow pump in for peace of mind.
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Great news!
 
Turboflash said:
At that level of boost for that long, IMO I think it's either out of fuel (as I previously questioned) or head/pistons get so hot, it goes into big-time deto and knock protection shuts it off. Ask me why I think this. Hint, I just finished rebuilding my engine.
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Who's tune when your engine went down?
 
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