Cougsfan

Not being a diesel expert and wanting to learn more; Can someone steer me to a thread or article describing how the waste gate works and how it is controlled? I assume what the waste gate does is control the amount of turbo boost you get depending on the load. I also assume what it does is stay open, dumping the compressed air from the turbo under no load conditions, and closes allowing pressure to build up in the inlet tract as load increases. Are those assumptions right? How does it know the load?

BigIron70

Turbo video shows basic operation

Cougsfan

Thanks Big Iron, That was worth watching . It showed me a lot about a Turbocharger I have not seen as I have never taken mine off. But it didn't explain the controls associated with the waste gate. What tells it to open or close? How does the engine know it should utilize more or less turbo boost?

gorms

The turbo starts "lighting" by the motor supplying more fuel via the exhaust side. On mechanical trucks like ours there is a "aneroid fuel control" which limits how much fuel is delivered compared to how much boost the turbo is supplying the motor. So as you start out, the fuel is limited to basically just enough to get going and also get the turbo going a bit. As boost builds, the AFC moves out of the way (supposed to be gradual, can be adjusted) and lets the pump supply full fuel at around full boost.

Basically load on the engine is what determines how much boost is made by the turbo. The wastegate is just an actuator that works on manifold pressure (boost) and opens up at a set point. Stock is somewhere around 18psi, which is when it opens up the wastegate letting exhaust gas go around the turbine wheel instead of through it, lowering the energy going into/out of the turbo. It's all a balancing act to say the least! Hope this makes sense.

BigIron70

The old guy sure does like spinning that turbo over with his fingers. Never ever try to do that under fluorescent light with the engine running. The light will make turbo look as if it isn't spinning, like a timing light on a gas engine, since it is spinning at the same frequency as fluorescent light. You may be tempted to stick finger into turbo to see if it is spinning, believe me it's spinning. It will be spinning at 16,000 rpm or higher at idle. Would take your fingers off instantly. So never run engine with air intake off the turbo. I hope by posting this I saved somebody from losing their fingers.

Cougsfan

Ok, I think I have learned a few things; The waste gate dumps (or bypasses) exhaust gas around the turbo, not compressed inlet air, like I thought. Secondly, the waste gate serves as a pressure limiter, or relief valve, not letting the exhaust gas make excessive pressure in the inlet. Finally the boost isn't really controlled by the waste gate. It is controlled by stepping on the gas and dumping more fuel into the engine.

Is that all correct?

gorms

Yup! Alot of gas cars run a dump valve on the air side, since they have a throttle that closes when you let off the gas. Gotta give the air a place to go, not so much with diesels.

infidel

http://dodgeram.org/tech/dsl/FAQ/turbo_faq.htm