<p>I don't know what was the object like in your plans but it looks like your extruder stopped pushing filament well. I had similar effect when I used extensive retraction with low quality filament. In fact filament was to soft and when it was pressed to hobbed pulley/bolt it became flatened and then stopped flowing. So if your case is similar you could check the following:</p>

<ul>
<li>spring tenssion</li>
<li>knurls</li>
<li>filament diameter</li>
</ul>

<p>It's also worth to check if hobbed pulley is screwed tight on motor shaft.</p>

<p><strong>[edit]</strong></p>

<p>It could be also caused by too fast retraction if knurls are not sharp enough they can slide on or scrap filament.</p>

<p>When you notice that again, stop printing proces, lose springs and pull out filament from hotend and inspect its shape.</p>

CC BY-SA 3.0
2016-05-24T12:15:07.387Z
@TormodHaugene that was my first thought too...
darth pixel
CC BY-SA 3.0
2016-05-24T14:02:23.030Z
If it was made in the last couple years, it has a PTFE-lined hot end. Checking the condition of the PTFE liner would be a very good troubleshooting step. If it's charred/degraded, it can cause this. Checking the extruder spring arm tension is another good one.
Ryan Carlyle
CC BY-SA 3.0
2016-05-24T07:21:46.097Z
2016-05-25T06:11:12.000Z
2016-05-25T06:11:12.000Z
darth pixel
<p>Quick Question.
My Printer is the CTC clone of the Makerbot Replicator Dual.</p>

<p>For my past few prints after <code>nth</code> layer the print just starts to go stringy. Here is an example:</p>

<p><a href="https://i.sstatic.net/77OYQ.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/77OYQ.jpg" alt="Stringy Print"></a></p>

<p>I am currently using MakerWare with the following settings</p>

<pre><code>{
   "_attached_extruders" : [ "mk8", "mk8" ],
   "_bot" : "replicatordual",
   "_extruders" : [ 0 ],
   "_materials" : [ "pla", "pla" ],
   "adjacentFillLeakyConnections" : false,
   "adjacentFillLeakyDistanceRatio" : 0,
   "anchorExtrusionAmount" : 5.0,
   "anchorExtrusionSpeed" : 2.0,
   "anchorWidth" : 2.0,
   "backlashEpsilon" : 0.050,
   "backlashFeedback" : 0.90,
   "backlashX" : 0.0,
   "backlashY" : 0.090,
   "bedZOffset" : 0.0,
   "bridgeAnchorMinimumLength" : 0.80,
   "bridgeAnchorWidth" : 0.80,
   "bridgeMaximumLength" : 80.0,
   "bridgeSpacingMultiplier" : 1.0,
   "coarseness" : 9.999999747378752e-005,
   "commentClose" : "",
   "commentOpen" : ";",
   "computeVolumeLike2_1_0" : false,
   "defaultExtruder" : 0,
   "defaultRaftMaterial" : 0,
   "defaultSupportMaterial" : 0,
   "description" : "",
   "doAnchor" : true,
   "doBacklashCompensation" : false,
   "doBreakawaySupport" : false,
   "doBridging" : true,
   "doDynamicSpeed" : false,
   "doDynamicSpeedGradually" : true,
   "doDynamicSpeedInteriorShells" : false,
   "doDynamicSpeedOutermostShell" : true,
   "doExponentialDeceleration" : false,
   "doExternalSpurs" : true,
   "doFixedLayerStart" : false,
   "doFixedShellStart" : true,
   "doInfills" : true,
   "doInsets" : true,
   "doInternalSpurs" : false,
   "doMixedRaft" : true,
   "doMixedSupport" : true,
   "doOutlines" : true,
   "doPrintLayerMessages" : false,
   "doPrintProgress" : true,
   "doPurgeWall" : false,
   "doRaft" : false,
   "doSplitLongMoves" : true,
   "doSupport" : false,
   "doSupportUnderBridges" : false,
   "endGcode" : "",
   "exponentialDecelerationMinSpeed" : 0.0,
   "extruderProfiles" : [
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      },
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      }
   ],
   "extruderTemp0" : 208,
   "extruderTemp1" : 200,
   "extrusionProfiles" : {
      "bridges" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "firstLayer" : {
         "fanSpeed" : 0.50,
         "feedrate" : 5.0
      },
      "firstLayerRaft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 50.0
      },
      "floorSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "infill" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "insets" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "outlines" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "raft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "raftBase" : {
         "fanSpeed" : 0.50,
         "feedrate" : 10.0
      },
      "roofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "sparseRoofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      }
   },
   "fixedLayerStartX" : 0.0,
   "fixedLayerStartY" : 0.0,
   "fixedShellStartDirection" : 215.0,
   "floorSolidThickness" : 0,
   "floorSurfaceThickness" : 0,
   "floorThickness" : 2.0,
   "gridSpacingMultiplier" : 0.990,
   "infillDensity" : 0.05000000074505806,
   "infillOrientationInterval" : 90,
   "infillOrientationOffset" : 0,
   "infillOrientationRange" : 90,
   "infillShellSpacingMultiplier" : 0.70,
   "insetDistanceMultiplier" : 1.0,
   "jsonToolpathOutput" : false,
   "layerHeight" : 0.250,
   "leakyConnectionsAdjacentDistance" : 0.0,
   "maxConnectionLength" : 10.0,
   "maxSparseFillThickness" : 0.250,
   "maxSpurWidth" : 0.50,
   "minLayerDuration" : 5.0,
   "minLayerHeight" : 0.010,
   "minRaftBaseGap" : 0.0,
   "minSpeedMultiplier" : 0.30,
   "minSpurLength" : 0.340,
   "minSpurWidth" : 0.120,
   "minThickInfillImprovement" : 1.0,
   "modelFillProfiles" : {},
   "numberOfShells" : 3,
   "platformTemp" : 70,
   "purgeBucketSide" : 4.0,
   "purgeWallBaseFilamentWidth" : 2.0,
   "purgeWallBasePatternLength" : 10.0,
   "purgeWallBasePatternWidth" : 8.0,
   "purgeWallModelOffset" : 2.0,
   "purgeWallPatternWidth" : 2.0,
   "purgeWallSpacing" : 1.0,
   "purgeWallWidth" : 0.50,
   "purgeWallXLength" : 30.0,
   "raftAligned" : true,
   "raftBaseAngle" : 0.0,
   "raftBaseDensity" : 0.6999999880790710,
   "raftBaseLayers" : 1,
   "raftBaseRunGapRatio" : 0.8000000119209290,
   "raftBaseRunLength" : 15.0,
   "raftBaseThickness" : 0.3000000119209290,
   "raftBaseWidth" : 2.50,
   "raftExtraOffset" : 0.0,
   "raftFillProfiles" : {},
   "raftInterfaceAngle" : 45.0,
   "raftInterfaceDensity" : 0.3000000119209290,
   "raftInterfaceLayers" : 2,
   "raftInterfaceThickness" : 0.2700000107288361,
   "raftInterfaceWidth" : 0.4000000059604645,
   "raftModelSpacing" : 0.2199999988079071,
   "raftOutset" : 4.0,
   "raftSurfaceAngle" : 0.0,
   "raftSurfaceLayers" : 3,
   "raftSurfaceShellSpacingMultiplier" : 0.70,
   "raftSurfaceShells" : 2,
   "raftSurfaceThickness" : 0.2700000107288361,
   "roofAnchorMargin" : 0.40,
   "roofSolidThickness" : 0,
   "roofSurfaceThickness" : 0,
   "roofThickness" : 2.0,
   "shellsLeakyConnections" : false,
   "solidFillOrientationInterval" : 90,
   "solidFillOrientationOffset" : -45,
   "solidFillOrientationRange" : 90,
   "sparseInfillPattern" : "hexagonal",
   "splitMinimumDistance" : 0.40,
   "spurOverlap" : 0.0010,
   "startGcode" : "",
   "startPosition" : {
      "x" : -112,
      "y" : -73,
      "z" : 0
   },
   "supportAligned" : true,
   "supportAngle" : 68.0,
   "supportDensity" : 0.2000000029802322,
   "supportExcessive" : false,
   "supportExtraDistance" : 0.50,
   "supportFillProfiles" : {},
   "supportLayerHeight" : 0.250,
   "supportLeakyConnections" : true,
   "supportModelSpacing" : 0.4000000059604645,
   "supportRoofModelSpacing" : 0.4000000059604645,
   "thickLayerThreshold" : 0,
   "thickLayerVolumeMultiplier" : 1,
   "travelSpeedXY" : 150.0,
   "travelSpeedZ" : 23.0,
   "version" : "3.9.3"
}
</code></pre>

<p>If anybody has any ideas please let me know.</p>

<p>Thank You</p>

CC BY-SA 3.0
2016-05-24T11:58:14.653Z
Does the issue appear after the printer has "changed action", such as started to print an area that require very frequent retraction? Also, does this happen only for *one* or several different models?
Tormod Haugene
<makerbot><pla><replicator-dual><makerware>
3D Printer Stringing after nth layer
Robert Lerman
# 3D Printer Stringing after nth layer

(Asked by: username_0 on 2016-05-24)

Quick Question.
My Printer is the CTC clone of the Makerbot Replicator Dual.

For my past few prints after `nth` layer the print just starts to go stringy. Here is an example:

[![Stringy Print](https://i.sstatic.net/77OYQ.jpg)](https://i.sstatic.net/77OYQ.jpg)

I am currently using MakerWare with the following settings

```
{
   "_attached_extruders" : [ "mk8", "mk8" ],
   "_bot" : "replicatordual",
   "_extruders" : [ 0 ],
   "_materials" : [ "pla", "pla" ],
   "adjacentFillLeakyConnections" : false,
   "adjacentFillLeakyDistanceRatio" : 0,
   "anchorExtrusionAmount" : 5.0,
   "anchorExtrusionSpeed" : 2.0,
   "anchorWidth" : 2.0,
   "backlashEpsilon" : 0.050,
   "backlashFeedback" : 0.90,
   "backlashX" : 0.0,
   "backlashY" : 0.090,
   "bedZOffset" : 0.0,
   "bridgeAnchorMinimumLength" : 0.80,
   "bridgeAnchorWidth" : 0.80,
   "bridgeMaximumLength" : 80.0,
   "bridgeSpacingMultiplier" : 1.0,
   "coarseness" : 9.999999747378752e-005,
   "commentClose" : "",
   "commentOpen" : ";",
   "computeVolumeLike2_1_0" : false,
   "defaultExtruder" : 0,
   "defaultRaftMaterial" : 0,
   "defaultSupportMaterial" : 0,
   "description" : "",
   "doAnchor" : true,
   "doBacklashCompensation" : false,
   "doBreakawaySupport" : false,
   "doBridging" : true,
   "doDynamicSpeed" : false,
   "doDynamicSpeedGradually" : true,
   "doDynamicSpeedInteriorShells" : false,
   "doDynamicSpeedOutermostShell" : true,
   "doExponentialDeceleration" : false,
   "doExternalSpurs" : true,
   "doFixedLayerStart" : false,
   "doFixedShellStart" : true,
   "doInfills" : true,
   "doInsets" : true,
   "doInternalSpurs" : false,
   "doMixedRaft" : true,
   "doMixedSupport" : true,
   "doOutlines" : true,
   "doPrintLayerMessages" : false,
   "doPrintProgress" : true,
   "doPurgeWall" : false,
   "doRaft" : false,
   "doSplitLongMoves" : true,
   "doSupport" : false,
   "doSupportUnderBridges" : false,
   "endGcode" : "",
   "exponentialDecelerationMinSpeed" : 0.0,
   "extruderProfiles" : [
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      },
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      }
   ],
   "extruderTemp0" : 208,
   "extruderTemp1" : 200,
   "extrusionProfiles" : {
      "bridges" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "firstLayer" : {
         "fanSpeed" : 0.50,
         "feedrate" : 5.0
      },
      "firstLayerRaft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 50.0
      },
      "floorSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "infill" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "insets" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "outlines" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "raft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "raftBase" : {
         "fanSpeed" : 0.50,
         "feedrate" : 10.0
      },
      "roofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "sparseRoofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      }
   },
   "fixedLayerStartX" : 0.0,
   "fixedLayerStartY" : 0.0,
   "fixedShellStartDirection" : 215.0,
   "floorSolidThickness" : 0,
   "floorSurfaceThickness" : 0,
   "floorThickness" : 2.0,
   "gridSpacingMultiplier" : 0.990,
   "infillDensity" : 0.05000000074505806,
   "infillOrientationInterval" : 90,
   "infillOrientationOffset" : 0,
   "infillOrientationRange" : 90,
   "infillShellSpacingMultiplier" : 0.70,
   "insetDistanceMultiplier" : 1.0,
   "jsonToolpathOutput" : false,
   "layerHeight" : 0.250,
   "leakyConnectionsAdjacentDistance" : 0.0,
   "maxConnectionLength" : 10.0,
   "maxSparseFillThickness" : 0.250,
   "maxSpurWidth" : 0.50,
   "minLayerDuration" : 5.0,
   "minLayerHeight" : 0.010,
   "minRaftBaseGap" : 0.0,
   "minSpeedMultiplier" : 0.30,
   "minSpurLength" : 0.340,
   "minSpurWidth" : 0.120,
   "minThickInfillImprovement" : 1.0,
   "modelFillProfiles" : {},
   "numberOfShells" : 3,
   "platformTemp" : 70,
   "purgeBucketSide" : 4.0,
   "purgeWallBaseFilamentWidth" : 2.0,
   "purgeWallBasePatternLength" : 10.0,
   "purgeWallBasePatternWidth" : 8.0,
   "purgeWallModelOffset" : 2.0,
   "purgeWallPatternWidth" : 2.0,
   "purgeWallSpacing" : 1.0,
   "purgeWallWidth" : 0.50,
   "purgeWallXLength" : 30.0,
   "raftAligned" : true,
   "raftBaseAngle" : 0.0,
   "raftBaseDensity" : 0.6999999880790710,
   "raftBaseLayers" : 1,
   "raftBaseRunGapRatio" : 0.8000000119209290,
   "raftBaseRunLength" : 15.0,
   "raftBaseThickness" : 0.3000000119209290,
   "raftBaseWidth" : 2.50,
   "raftExtraOffset" : 0.0,
   "raftFillProfiles" : {},
   "raftInterfaceAngle" : 45.0,
   "raftInterfaceDensity" : 0.3000000119209290,
   "raftInterfaceLayers" : 2,
   "raftInterfaceThickness" : 0.2700000107288361,
   "raftInterfaceWidth" : 0.4000000059604645,
   "raftModelSpacing" : 0.2199999988079071,
   "raftOutset" : 4.0,
   "raftSurfaceAngle" : 0.0,
   "raftSurfaceLayers" : 3,
   "raftSurfaceShellSpacingMultiplier" : 0.70,
   "raftSurfaceShells" : 2,
   "raftSurfaceThickness" : 0.2700000107288361,
   "roofAnchorMargin" : 0.40,
   "roofSolidThickness" : 0,
   "roofSurfaceThickness" : 0,
   "roofThickness" : 2.0,
   "shellsLeakyConnections" : false,
   "solidFillOrientationInterval" : 90,
   "solidFillOrientationOffset" : -45,
   "solidFillOrientationRange" : 90,
   "sparseInfillPattern" : "hexagonal",
   "splitMinimumDistance" : 0.40,
   "spurOverlap" : 0.0010,
   "startGcode" : "",
   "startPosition" : {
      "x" : -112,
      "y" : -73,
      "z" : 0
   },
   "supportAligned" : true,
   "supportAngle" : 68.0,
   "supportDensity" : 0.2000000029802322,
   "supportExcessive" : false,
   "supportExtraDistance" : 0.50,
   "supportFillProfiles" : {},
   "supportLayerHeight" : 0.250,
   "supportLeakyConnections" : true,
   "supportModelSpacing" : 0.4000000059604645,
   "supportRoofModelSpacing" : 0.4000000059604645,
   "thickLayerThreshold" : 0,
   "thickLayerVolumeMultiplier" : 1,
   "travelSpeedXY" : 150.0,
   "travelSpeedZ" : 23.0,
   "version" : "3.9.3"
}

```

If anybody has any ideas please let me know.

Thank You

**Tags:** makerbot, pla, replicator-dual, makerware

> **Comments:**
> **username_1**: Does the issue appear after the printer has "changed action", such as started to print an area that require very frequent retraction? Also, does this happen only for *one* or several different models?  

---

## 1 answers

### Answer by username_2 on 2016-05-24. Score: 2

I don't know what was the object like in your plans but it looks like your extruder stopped pushing filament well. I had similar effect when I used extensive retraction with low quality filament. In fact filament was to soft and when it was pressed to hobbed pulley/bolt it became flatened and then stopped flowing. So if your case is similar you could check the following:

* spring tenssion
* knurls
* filament diameter

It's also worth to check if hobbed pulley is screwed tight on motor shaft.

**[edit]**

It could be also caused by too fast retraction if knurls are not sharp enough they can slide on or scrap filament.

When you notice that again, stop printing proces, lose springs and pull out filament from hotend and inspect its shape.

> **Comments:**
> **username_2**: @username_1 that was my first thought too...  
> **username_3**: If it was made in the last couple years, it has a PTFE-lined hot end. Checking the condition of the PTFE liner would be a very good troubleshooting step. If it's charred/degraded, it can cause this. Checking the extruder spring arm tension is another good one.  

---

