Now the right cylinder bank is feed before the left from the same line so we checked the right AVCS screen as well. To get to it, we had to remove our large air inlet for our Cobb Tuning air box that we had fabricated to make room. We think you might not have to do this if your car has a stock air intake or a rotated mount turbo.
Using the same technique to avoid taking the fitting off the fuel rail we remove the right banjo bolt. The Screen was already removed here as well. What now?
There is one more filter screen on this oil circuit. The external line that feeds the AVCS sprockets feeds the turbo first! Now we were wondering if this screen clogged up. It would make sense if the screen started to clog, the last part to get oil, the left cylinder bank AVCS sprocket would stop working first, then as it got worse, the right bank would stop working. The Precision Turbo has a ball-bearing center section that doesn’t require much oil flow but even though it is fed from the oil galley first, it would have problems last. This is how it went in our car.
So we had to check this last screen. It is found in the banjo bolt at the backside of the engine on the right side as shown here.
When we removed the bolt and took the fitting out of it, it was filled with a jelled oil glop. What had happened is Christa only drives about 4 miles a day during the school week so her car never warms up fully until she drives on the weekends where she drives farther visiting friends. Even though we use the best synthetic oil and change the oil every 3000 miles, the lack of heat allowed moisture and Ethanol residue from the E85 fuel to mix and form a jellied glop. This glop eventually clogged the turbo pre-filter and gradually cut off the oil supply to first the AVCS system then the turbo.
We checked our turbo and found it didn’t spin as freely as your typical ball bearing turbo and had some axial play in the shaft. For a ball bearing turbo, some radial play is acceptable but zero axial play is. We sent the turbo back to Precision and sure enough, it was not ruined but needed a rebuild. Instead of rebuilding the turbo they are going to be sending a Second Generation improved version of this turbo for us to evaluate!
We will also be leaving the turbo pre-filter out of the Bajo fitting when we put it all back together as many Subaru tuners do.
- If your Subie WRX/STi throws a p0011 and or p0021 code, check your filter screens first to hopefully avoid turbo damage.
- If you spend a lot of time doing extremely short hop driving, your oil change intervals should probably be something like every 1500 miles, especially when running E85 which runs cooler and moister. An engine’s oil needs to get up to operating temperature to drive off water and the volatile parts of combustion residue of which E85 makes much more than gasoline.
- Doing some research on these common codes on NASIOC would have saved some grief as just a little digging showed that treating the issue as an electrical issue first has caused quite a few nuked turbos. I am notorious about hating forums but NASIOC has good info and the Subaru online community isn’t as bad as many.
At least we are going to get to evaluate a new Gen II Precision direct factory replacement turbo in the process! Stay tuned for that.