Acceleration shudder over 80 "solved"

[shaldaya]

This is to help the other people that said they had the same problem
I made a thread earlier stating a problem with engine shudder (https://shoforum.com/threads/acceleration-shudder-over-80.145249/#post-1588736)

I found the issue, and it was a vacuum line between the two exhaust lines that came off on the top left area of the engine
In the area if the photo

 

[Ecoboost_xsport]

That's your boost solenoid. One line comes in from the intake plumbing, then splits and goes to each wastegate.

At least that's what you're showing in the picure. Which line came off, btw? Feel free to circle the part.

 

[shaldaya]

Was this hose specifically
I either lost the clamp or someone forgot to put it back on

 

[Ecoboost_xsport]

Was this hose specifically
I either lost the clamp or someone forgot to put it back on

Ah ok....yeah, your turbos weren't getting any boost reference. The wastegates were opening on spring pressure alone, which is about 3 to 4psi. You just weren't getting any boost built up.

 

[toms89]

Ah ok....yeah, your turbos weren't getting any boost reference. The wastegates were opening on spring pressure alone, which is about 3 to 4psi. You just weren't getting any boost built up.

I think the opposite would be true. With no boost supplied to the wastegate canisters they would not open and the turbo's would build as much boost as they are capable of.

I believe the the pcm effectively disconnects the boost reference by closing the solenoid when going to 100% wastegate duty cycle. This allows the pcm to control boost. When the pcm goes to 0% duty cycle it gives full boost reference to the solenoids and wastegates open based on what the wastegates are mechanically set for.

Please correct me if I am wrong.

My guess is the pcm recognized the boost was exceeding what was commanding and it started manipulating the throttle and/or bypass valves to control it since the wastegates were not dropping the boost.

 

[Ecoboost_xsport]

I think the opposite would be true. With no boost supplied to the wastegate canisters they would not open and the turbo's would build as much boost as they are capable of.

I believe the the pcm effectively disconnects the boost reference by closing the solenoid when going to 100% wastegate duty cycle. This allows the pcm to control boost. When the pcm goes to 0% duty cycle it gives full boost reference to the solenoids and wastegates open based on what the wastegates are mechanically set for.

Please correct me if I am wrong.

My guess is the pcm recognized the boost was exceeding what was commanding and it started manipulating the throttle and/or bypass valves to control it since the wastegates were not dropping the boost.

No, there are springs inside the wastegates that are set to about 4psi. The boost pressure keeps the wastegate closed, then releases. With no boost reference, they rely on the spring pressure alone. This is how they are designed.

 

[toms89]

This video explains it pretty well.

The "boost controller" described in the video is the pcm in our case and it controls boost beyond wastegate spring pressure via the boost solenoid. 100% wastegate duty cycle indicates the pcm is bleeding all boost reference to the wastegates as described in the video. 0% wdc and the wastegates receive all boost reference and will open at wastegate spring pressure. It follows that you can bleed off any percentage in between.

I had modified vehicles in the past tuned and built by myself. Including a 10 second V2 Vortech foxbody mustang and a 12 second Eaton supercharged 2000 expedition. The Sho is my 1st adventure with turbo's so I am learning. I know turbo's are tricky to tune so I leave that up to Brad.

Anyhow I initially did believed that wastegate duty cycle was how much boost was referenced to the wastegates as mentioned. Not sure if I saw it on this site or just web in general. Never really questioned it or thought it through. Made sense to me but the term "wastegate duty cycle" is misleading and where I believe much of the confusion comes from.

So I get my new stage 3 turbo's with them physically in hand and confirm what pressure the wastegates are setup for because Brad wanted me to make sure they had stock spring pressure. Testing them made it quite clear that boost on the wastegate canisters opens the wastegates and the higher the boost the more they open, not vise versa. Now this did not fly with what I understood at the time so I began to research. It became clear via researching then testing the hardware to confirm, that wastegate duty cycle is actually how much boost the pcm is bleeding off. If you test the boost solenoid you will find that the wastegate canister port is connected to boost reference port at 0% duty cycle. (turned off) When the boost solenoid is on it disconnects the wastegate canister port from the boost reference port. (bleeding off the boost) I believe if the term "wastegate duty cycle" was "boost solenoid duty cycle" in our setup it would more accurately describe what is happening and be less confusing.

 

[Shaggy]

This is to help the other people that said they had the same problem
I made a thread earlier stating a problem with engine shudder (https://shoforum.com/threads/acceleration-shudder-over-80.145249/#post-1588736)

I found the issue, and it was a vacuum line between the two exhaust lines that came off on the top left area of the engine
In the area if the photo

Thanks for updating the post showing with the issues was and how you fixed it!