I believe I've found the culprit!
While conducting pre-race checks in the engine bay I discovered
a vacuum line has been rubbing on the supercharger's upper pulley. It had worn through the foam sleeve and half-way through the plastic vacuum line. This is apparently the vacuum line supplying negative pressure to the clean-side PCV catch can.
I performed a temporary repair so I could still go racing:
- Cut the surrounding foam sleeve around its circumference for access.
- Wrapped electrical tape around the damaged portion of the plastic vacuum line.
- Secured the vacuum line to its neighboring PCV line to reposition it above the pulley. The heat and pressure had apparently reset the bends in the plastic line.
Here is the damage to the plastic vacuum line:
Here's the temporary repair:
A zip-tie to push the line back where it belongs:
Back to normal:
The engine seems to have regained all its power now. I noticed an immediate improvement in responsiveness and there were no engine cut-outs at the track on Sunday.
I wondered why it was positioned so close to the pulley in the first place, though. At first I thought it must have just relaxed over time because there's really no solid mounted stand-off bracket for these lines. They're loosely bound with plastic loops to adjacent lines. Looking back at older photos of my engine bay, it became apparent that the coolant recovery tank line had been improperly routed, probably when I changed plugs Mar 2017. It was putting pressure on the vacuum line pulling it toward the pulley.
Here's how the lines were routed when I took delivery 30 Dec 2016:
(Compare lines within green box to next photo)
While changing plugs last Friday I did notice that the recovery tank line was out of place but it didn't dawn on me at the time that it was pulling on the vacuum line. I went ahead and re-routed it when I put everything back together.
I found this photo in a set I took on 27 Jul 2017:
Only thing that happened between delivery and July was change of spark plugs.
Now I just have to order a replacement line and install it.
--Cal