The 'only' (current) Sportsman flying with the UL Power 520T had an issue come up approx a year ago where the boost / manifold pressure would fluctuate. I was fortunate enough to be around and help him troubleshoot this, and more importantly understand how the system works better.
The Turbo is powered by the exhaust (obviously)... But the amount of exhaust gas that hits the turbo is regulated by the waste gate, which is essentially a valve. There is a spring in the waste gate that 'normally' regulates when the valve opens to start releasing pressure as to not overboost the engine. The standard spring will fully open the valve at 3" HG above ambient which is about 6 PSI.
Enter the Boost Controller... The Boost Controller 'fools' the spring on the waste gate to allow turbo to spin faster and deliver higher than 3" HG / 6PSI to the intake. There is a pressure sensor on the ECU in the cockpit, determines what the Boost Controller needs to do.
Below is from the UL manual... and shows the connections.
The boost controller is essentially another valve. It connects the pressure of the intake manifold and the waste gate. When the Boost Controller is allowing the turbo to spool up, ONLY those two lines are connected. The 3rd port on the Boost Controller is a vent. When an overboost situation is coming (IE Full Throttle) the Boost Controller vents the pressure from the intake manifold to let Waste Gate open up and drop the speed of the turbo.
The target pressure max manifold pressure is 39.5" HG, or roughly 20 lbs of boost.
In the case of the 'other' Sportman...
- The problem just started on day. Nothing had changed (IE ECU firmware) that would have precipitated the issue.
- At full throttle / boost, the engine would start surging... 1 to 2" HG surge. Pulling the throttle back would stop the surging.
- Disconnecting the Boost Controller would stop the problem. However, now you are limited to about 33" HG of manifold pressure. The turbo is not working to its intended potential, but no surging.
- Many troubleshooting steps were taken.
- UL sent a new boost controller, as well as a new ECU with special firmware. They changed to update rate on the boost controller from 30 Hz to 10 Hz. This did change the problem and make it not as noticable, and the surging delta of inHG was less, but the problem remained.
- The eventual solution... move the boost controller. In this install, the Boost Controller was installed low on the pilots side of the firewall. The pressure lines went up to the top of the engine for the intake, and to the waste gate. The theory is they were too long. Relocating the boost controller completely corrected the issue. The original ECU and Boost Controller were reinstalled.
Not the fanciest bracket, but it should work. It's now very close to the intake manifold and waste gate. The problem is I have to extract the harness from the cockpit bundles and fish it through the firewall and dress it in. There are a lot of cable ties to cut...
