Quote:
Originally Posted by MightyMouseTech
I believe the N55 wastegate operates reverse of the N54. It needs vacuum to reduce boost. If there is no vacuum to the actuator, the wastegate is stuck closed.
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No.
N55 is the opposite of conventional wastegate controls.
Typical wastegate controls (like, pretty much every turbo engine from any other manufacturer) use both a spring (to keep the wastegate closed to a certain PSI, like 6-7psi, after which the wastegate will open without outside forces, as you’re literally pushing it open with exhaust gasses) as well as the boost pressure from intake manifold routed to the wastegate to KEEP it closed. They modulate boost by BLEEDING pressure away from that intake-to-wastegate-actuator line to allow the wastegate to open. (Yes, I realize that external wastegate exist
)
The N55 has two types:
EWG - easiest. You command a value and an electronic device modulates the wastegate position to an exact value regardless of boost/flow/etc.
PWG (the one most of us have) - has a spring as well, though the spring is something stupid low (2-4psi???? after which the wastegate will open without outside forces, as you’re literally pushing it open with exhaust gasses) and this is what may lead you to believe that “no vacuum means it’s closed.” That said, we DO use vacuum (produced by the vacuum pump) to PULL the wastegate CLOSED when boost pressure exceeds the wastegate spring. As such, you NEED vacuum to pull that wastegate closed under load/flow/boost. It’s also counter intuitive to say that the vacuum line “collapsed” and produced boost runaway, because we require MORE vacuum to keep the WG closed at higher exhaust flow (higher boost) because there is MORE pressure on the wastegate itself (because more exhaust flow).
If there is insufficient vacuum (no line connected, bad vacuum pump, bad solenoid, etc.), you will see no/little boost.
If there is excess vacuum (aka, really high WGDC [due to bad solenoid or poor tune]), you will see excessive boost.
At this point, the only thing I can think is that the WG actuator arm is not coming back to resting/open position. This can be due to a solenoid/line, or even physical issues like bends, rust/corrosion, bad actuator (damaged internals), bad turbo (as there is another pivot inside the exhaust side of the compressor), or uhhhhhhh something else pretty obvious (I haven’t had my coffee yet. It’s a Saturday mmmmmkay)