What is causing this wild temp swing?

[DJLind]

This has now happened a couple times recently. While smoking @ a low pit temp, the temp drops significantly, then zooms up to a very high temp, then it settles back down. Yesterday it happened twice in close succession. Here is the Fireboard graph from the session:

I had to scramble to get the fish pulled off the grill to keep them from ruin.
Does anyone know why something like this happens? I was using Traeger pellets for this run, but it happened on some Pit Boss pellets too.
Thanks.

 

[YYCRed]

This has now happened a couple times recently. While smoking @ a low pit temp, the temp drops significantly, then zooms up to a very high temp, then it settles back down. Yesterday it happened twice in close succession. Here is the Fireboard graph from the session:

View attachment 5314
I had to scramble to get the fish pulled off the grill to keep them from ruin.
Does anyone know why something like this happens? I was using Traeger pellets for this run, but it happened on some Pit Boss pellets too.
Thanks.

I've never seen that before, but where do you have your probe? That may help others answer your questions.

 

[RustyJake]

It looks a lot like an overshoot from having the door open. But it shouldn't overshoot that much regardless
Is it happening without even opening the door? The temp drop and spike sure look like what happens.
Grasping at straws here, is your grill software and firmware current and up to date?

 

[Puertex]

This has now happened a couple times recently. While smoking @ a low pit temp, the temp drops significantly, then zooms up to a very high temp, then it settles back down. Yesterday it happened twice in close succession. Here is the Fireboard graph from the session:

View attachment 5314
I had to scramble to get the fish pulled off the grill to keep them from ruin.
Does anyone know why something like this happens? I was using Traeger pellets for this run, but it happened on some Pit Boss pellets too.
Thanks.

These are the steps I would check first before I even call Traeger.
They may ask you similar questions and I would rather have some answers for them.
Out of curiosity, what temperature was the Traeger ambient probe registering at the time?
Did it show the same upset?
Notice that the temp went down first before it overshot. The sudden increase may be a reaction (overshooting) by the controller sensing that the temp went down first and then it overreacted. Is the auger feeding freely? Are there any obstructions? What kind of pellets are being used?
What were the outside conditions? Was it windy around the smoker? Did you open the lid?
Was there an electrical blip in the house?
Has the firepot been cleaned out on a regular basis?
Is the fan turning freely when observed?
If all the above reveal no potential culprits then it could be an issue with the fan and a call to Traeger may help you further diagnose the situation.
Just trying to troubleshoot...
Thanks,
Puertex

 

[DJLind]

I've never seen that before, but where do you have your probe? That may help others answer your questions.

The Traeger probe is in the factory position. The FireBoard pit probe is toward the right rear corner, a few inches from either edge.

 

[DJLind]

It looks a lot like an overshoot from having the door open. But it shouldn't overshoot that much regardless
Is it happening without even opening the door? The temp drop and spike sure look like what happens.
Grasping at straws here, is your grill software and firmware current and up to date?

Door wasn’t opened until I rescued the protein.

 

[Slimpicker]

The FireBoard pit probe is toward the right rear corner, a few inches from either edge.

Isn't that a bad hot spot place to put an ambient probe in that grill??

Most of us put the fireboard ambient probe close to the Traeger Probe to learn the grill better.

 

[DJLind]

These are the steps I would check first before I even call Traeger.
They may ask you similar questions and I would rather have some answers for them.
Out of curiosity, what temperature was the Traeger ambient probe registering at the time?
Did it show the same upset?
Notice that the temp went down first before it overshot. The sudden increase may be a reaction (overshooting) by the controller sensing that the temp went down first and then it overreacted. Is the auger feeding freely? Are there any obstructions? What kind of pellets are being used?
What were the outside conditions? Was it windy around the smoker? Did you open the lid?
Was there an electrical blip in the house?
Has the firepot been cleaned out on a regular basis?
Is the fan turning freely when observed?
If all the above reveal no potential culprits then it could be an issue with the fan and a call to Traeger may help you further diagnose the situation.
Just trying to troubleshoot...
Thanks,
Puertex

Thanks for the thoughtful response.
The Traeger probe reported the same temp pattern.
Traeger pellets this time, Pit Boss another time.
Don’t know how to tell if there was a clog/jam leading up to the temp drop. I do know that the blower was running the entire time the temp was low.
Nice warm Florida day. No breeze around the grill.
I clean the grill regularly and this was the 2nd cook since last thorough clean out.

 

[DJLind]

Isn't that a bad hot spot place to put an ambient probe in that grill??

Actually, that position yields temps consistent with when I positioned it right next to the factory thermometer. The Traeger setting was 185 and the FireBoard was reporting in the 160’s.

 

[Puertex]

Actually, that position yields temps consistent with when I positioned it right next to the factory thermometer. The Traeger setting was 185 and the FireBoard was reporting in the 160’s.

OK, with the smoker cooled down, not cooking or fired, firepot clean, I would remove the covers and jog the auger to see it consistently (maybe a few minutes) feed the pellets to the firepot. You should be able to do this without heating/firing the pellets.
I would be watching for any sudden stops or start/stop behavior.

* Please don't put your fingers or hand near the auger or any moving parts.*

With the auger stopped, the pellets from the firepot may be recovered for later use...
After this, having done these observations, maybe a call to Traeger for further guidance may be necessary.
Puertex

 

[DJLind]

OK, with the smoker cooled down, not cooking or fired, firepot clean, I would remove the covers and jog the auger to see it consistently (maybe a few minutes) feed the pellets to the firepot. You should be able to do this without heating/firing the pellets.
I would be watching for any sudden stops or start/stop behavior.

* Please don't put your fingers or hand near the auger or any moving parts.*

With the auger stopped, the pellets from the firepot may be recovered for later use...
After this, having done these observations, maybe a call to Traeger for further guidance may be necessary.
Puertex

Thanks Puertex, I'll give that a try.

 

[RemE]

I agree with the trouble shooting, the controller lost control. Its only feedback is the pit temp probe. If the fire died down, the controller feeds pellets to recover.

It's the cause of the sudden drop off, while cruzing normally that we need to find. It seems logical to look closely at the auger, if it stalled, say from a pellet jam, but recovered, this could happen. Fans kinda work till they don't.

Something killed the fire, loss of fuel, or air, are the only variables (assuming no wind or open hood).

I don't know if a power glitch could trigger a re-ignite cycle, vs just a flat shutdown. But a short jam or bind of the auger could force an ignition cycle with pellet over-feed and temp spike.

Personally I'd, empty the hopper, fully clear the auger, inspect both ends.

 

[DJLind]

I agree with the trouble shooting, the controller lost control. Its only feedback is the pit temp probe. If the fire died down, the controller feeds pellets to recover.

It's the cause of the sudden drop off, while cruzing normally that we need to find. It seems logical to look closely at the auger, if it stalled, say from a pellet jam, but recovered, this could happen. Fans kinda work till they don't.

Something killed the fire, loss of fuel, or air, are the only variables (assuming no wind or open hood).

I don't know if a power glitch could trigger a re-ignite cycle, vs just a flat shutdown. But a short jam or bind of the auger could force an ignition cycle with pellet over-feed and temp spike.

Personally I'd, empty the hopper, fully clear the auger, inspect both ends.

Thanks. Your diagnosis makes sense to me. I'll do that.