A Little Stumped

[steiner]

Got a Stumble of some sorts.
First 2 days of the Give Away Ride weekend my Attak would stumble intermittently when over 8000rpm. I could pin it and it would hit 10,500 the speed would rise and then it would stumble. The rpm's would change but it felt like I was tapping the brake or hitting soft snow. Day three of the ride the fatal ER12 should up while warning up the sled in the am. Replaced the stator assembly and it was alive again. Thot that this was the cause of the stumble.
Yesterday went for a 230mile ride. Started the sled to back it of the truck and it was idling funny. Like it had a miss. While warming up it spit out code 34. Shut it off and started it again and the code was gone and idled just fine. So away we went. During the day the stumble would come back here and there. If the rpms were below 8000 it would not stumble but if they were over 8000 then once and awhile it would do it.
The only thing different this year on the sled is I changed the top gear to a 24 from a 23.
The stumble is weird. The rpms remain constant while it stumbles but the sled definitely slows down. Again it feels like the brakes are being applied or it is running thru soft snow. The slowing down part it very pronounced while the stumble is happening. I did hit 115mph on the dream meter with the change gearing.
All these runs over 8000 rpms were done on the open lake well packed trails. Lots of room to play with speed and rpm.
The sled has Ulmer clutching stage II I believe with a K helix wrapped 3-3. Primary cut for overdrive.
Motor is stock with 4500 miles on it and stock exhaust.
The skid was out for preseason work and all wheels and bearings are good and are still rolling free.
Dupont slides are still in excellent condition as well.
Would the gear changed do this? The only thing I thot the change would do was maybe make it a little sluggish from corner to corner, which is not the case.
Should I dig into the coils (code 34) or spark plugs or is this the beginning of the end of my ECM that has 19000miles on it?

 

[74Nitro]

Got a Stumble of some sorts.
First 2 days of the Give Away Ride weekend my Attak would stumble intermittently when over 8000rpm. I could pin it and it would hit 10,500 the speed would rise and then it would stumble. The rpm's would change but it felt like I was tapping the brake or hitting soft snow. Day three of the ride the fatal ER12 should up while warning up the sled in the am. Replaced the stator assembly and it was alive again. Thot that this was the cause of the stumble.
Yesterday went for a 230mile ride. Started the sled to back it of the truck and it was idling funny. Like it had a miss. While warming up it spit out code 34. Shut it off and started it again and the code was gone and idled just fine. So away we went. During the day the stumble would come back here and there. If the rpms were below 8000 it would not stumble but if they were over 8000 then once and awhile it would do it.
The only thing different this year on the sled is I changed the top gear to a 24 from a 23.
The stumble is weird. The rpms remain constant while it stumbles but the sled definitely slows down. Again it feels like the brakes are being applied or it is running thru soft snow. The slowing down part it very pronounced while the stumble is happening. I did hit 115mph on the dream meter with the change gearing.
All these runs over 8000 rpms were done on the open lake well packed trails. Lots of room to play with speed and rpm.
The sled has Ulmer clutching stage II I believe with a K helix wrapped 3-3. Primary cut for overdrive.
Motor is stock with 4500 miles on it and stock exhaust.
The skid was out for preseason work and all wheels and bearings are good and are still rolling free.
Dupont slides are still in excellent condition as well.
Would the gear changed do this? The only thing I thot the change would do was maybe make it a little sluggish from corner to corner, which is not the case.
Should I dig into the coils (code 34) or spark plugs or is this the beginning of the end of my ECM that has 19000miles on it?

Replace the sub harness for the coils. It's not the coils.

 

[MrSled]

When is the last time you changed the plugs? What is at steady throttle? Does it spike and hit Rev Limiter?

 

[maim]

un pin the coil plugs and check them. sounds like what we had on the phazer for one of the reasons it was bucking going down the trail. wire frayed right next to the crimp.

 

[Macheater]

When is the last time you changed the plugs? What is at steady throttle? Does it spike and hit Rev Limiter?

If you check/replace the plugs, check for the dreaded white powder corrosion crap that sometimes gets in the caps. Had that happen to mine.

 

[steiner]

When is the last time you changed the plugs? What is at steady throttle? Does it spike and hit Rev Limiter?

Plugs were inspected during the motor swap 1000 miles ago
Was not hitting the limiter. Stumble would happen at 8000-10500rpm
Would not let me continue a long wot run as it would continue to stumble erratically.

 

[earthling]

The code 34 error is pretty specific and RPM wouldn't change with an intermittent miss, power output would. Or it may change RPM too fast for the gauge to keep up. Swap coils around to eliminate the coil, but i like @74Nitro thoughts on the coil harness.

 

[74Nitro]

The code 34 error is pretty specific and RPM wouldn't change with an intermittent miss, power output would. Or it may change RPM too fast for the gauge to keep up. Swap coils around to eliminate the coil, but i like @74Nitro thoughts on the coil harness.

Easy way to test is to unplug the four connectors from the coils. Then take a male terminal like pictured and slide it into each female terminal in the connectors. It should grip firmly. If it's loose in any of them you just found the problem.
If you don't have a male connector you can remove the females from the connector and slide them individually onto the male terminals of the coil.

 

[pdiddy]

Maybe the calipers are grabbing at higher speeds since you had to remove them to change gears. Other than that sounds electrical, rev limiting, TORS, or bad connections.

 

[FlyinA]

Almost sounds like it's running short of fuel at high RPM. Could it be something as simple as dirty injectors, maybe caused by a load of #*$&@ gas? My first response to any engine stumble at any RPM is to try adding Sea Foam. It's surprising how often that takes care of the problem. Just a thought.

 

[kinger]

Any coincidence to fuel level? Mine on low fuel would stumble even though there was plenty of fuel in it yet, turns out it was water in fuel. Added some heat and then the yammi fuel treatment stuff and fixed it. This was back about 8 years ago. If your electrical plugs are tight on the coils then I would say it could be your ECU but dang that seems really unlikely.

 

[74Nitro]

Steiner, is this solved?

 

[steiner]

No. Unfortunately there is no time right now and trails are all shut down.

 

[steiner]

Well dug into it tonight. Found two wires from the coil harness that were rubbed into. Repaired them and looked into why they did that. A little clamp was rubbing on them and I guess once in a while they would both touch the clamp and cause the stumble.

 

[Stubbs]

Good find Steiner!