SSM 50530 - 1.5L Ecoboost Vibration and/Or Boom Noise while Driving

[PintoK]

Hello All,

Recently took in my 2022 Bronco Sport Big Bend (1.5L) as I felt some lugging/vibrations when trying to accelerate at around 1.5k RPM at Normal or Eco drive modes. The dealer was able to recreate it on my car as well as another one they had on stock and provided me with SSM 50530 and said it was normal. It seems like there really isn't anything they can do to mitigate the problem other than changing to Sport Mode.

Can anyone explain to me what is causing this issue? The way they explained it was not very clear. In addition, I can understand it is "normal", but what are the potential prolonged issues this may cause? I assume vibrations at any degree isn't really good in the long term.

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[Mark S.]

I think any explanation you get here is going to be speculation. That said, here's mine: Lugging is defined as increasing power demand (from the engine) at low RPM. The 3cyl engine incorporates a cylinder deactivation feature--no fuel goes to one cylinder--at low power demand (to improve fuel economy). Low power demand situations include steady speed at low RPM.

When you attempt to accelerate from a low power demand situation you first must increase power demand (by stepping on the accelerator). This creates a lugging scenario. To prevent lugging, the transmission must downshift to get the engine to a higher RPM. The computer controls when the transmission downshifts, and I believe the engineers prioritized fuel economy over smooth operation. The computer requires you to "prove" you want more power by stepping harder on the pedal. If you don't, the computer will keep the transmission in a higher gear, and maybe even keep a cylinder deactivated, resulting in better fuel economy, but slower acceleration and the vibration that's inherent in lugging an engine.

My reasoning for this speculation is that all of the owner reports I've read about this behavior that include experimentation with SPORT mode say this behavior is not present when you drive the car in SPORT mode. Why? Because the computer does two things that tend to avoid lugging the engine. First, it delays upshifts during acceleration so that the engine is a higher RPM. Second, it responds much more rapidly to power demands with an immediate downshift.

You can experiment yourself. Leave the car in NORMAL mode and drive at a speed/engine RPM where you notice the behavior. Instead of stepping slightly on the accelerator pedal for more speed, step HARD on the pedal. The greater the power demand (more accelerator pedal) the more rapidly the computer will downshift. Next, switch to SPORT mode. You should notice that the engine goes to a higher RPM before the transmission upshifts, and that it downshifts much more readily when you demand more power from a steady-state cruise condition.

 

[PintoK]

I think any explanation you get here is going to be speculation. That said, here's mine: Lugging is defined as increasing power demand (from the engine) at low RPM. The 3cyl engine incorporates a cylinder deactivation feature--no fuel goes to one cylinder--at low power demand (to improve fuel economy). Low power demand situations include steady speed at low RPM.

When you attempt to accelerate from a low power demand situation you first must increase power demand (by stepping on the accelerator). This creates a lugging scenario. To prevent lugging, the transmission must downshift to get the engine to a higher RPM. The computer controls when the transmission downshifts, and I believe the engineers prioritized fuel economy over smooth operation. The computer requires you to "prove" you want more power by stepping harder on the pedal. If you don't, the computer will keep the transmission in a higher gear, and maybe even keep a cylinder deactivated, resulting in better fuel economy, but slower acceleration and the vibration that's inherent in lugging an engine.

My reasoning for this speculation is that all of the owner reports I've read about this behavior that include experimentation with SPORT mode say this behavior is not present when you drive the car in SPORT mode. Why? Because the computer does two things that tend to avoid lugging the engine. First, it delays upshifts during acceleration so that the engine is a higher RPM. Second, it responds much more rapidly to power demands with an immediate downshift.

You can experiment yourself. Leave the car in NORMAL mode and drive at a speed/engine RPM where you notice the behavior. Instead of stepping slightly on the accelerator pedal for more speed, step HARD on the pedal. The greater the power demand (more accelerator pedal) the more rapidly the computer will downshift. Next, switch to SPORT mode. You should notice that the engine goes to a higher RPM before the transmission upshifts, and that it downshifts much more readily when you demand more power from a steady-state cruise condition.

Thanks for the explanation and you are right. As long as I step hard in normal or am in Sport mode I should be able to mitigate the issue from happening. That said, and maybe this is a dumb question, is lugging (and the vibrations that come with it) bad for the engine as it is trying to provide more power? While I will try my best to avoid it, there will be points where lugging will happen throughout the life of the car and wondering if there are any ill effects from it.

Will driving in Sport mode for longer periods of time have any impacts to the reliability of the vehicle as well?

 

[Mark S.]

Thanks for the explanation and you are right. As long as I step hard in normal or am in Sport mode I should be able to mitigate the issue from happening. That said, and maybe this is a dumb question, is lugging (and the vibrations that come with it) bad for the engine as it is trying to provide more power? While I will try my best to avoid it, there will be points where lugging will happen throughout the life of the car and wondering if there are any ill effects from it.

Will driving in Sport mode for longer periods of time have any impacts to the reliability of the vehicle as well?

Generally speaking, heavy lugging is not a good thing to do to an engine. The kind of lugging I'm talking about is prolonged and/or frequent wide-open throttle at low RPM. It appears the computer in your car will not let that happen. Clearly, it allows a certain amount of increased power demand before downshifting, but theoretically Ford's engineers programmed it to downshift before you can hurt the engine.

Driving in SPORT mode simply remaps the shift point and throttle response. Throttle response is how much power you get vs accelerator pedal position. In SPORT mode you get more power with less pedal movement. You cannot demand more power than the engine is capable of producing, so throttle response is not a significant factor in engine wear. All things being equal, higher RPM does increase wear, so the fact the computer allows the engine to get to a higher RPM before upshifting will increase wear over NORMAL mode. How much? My educated guess is not significantly. If you drive it like Racer Rob, allowing the engine to wind up to redline or near redline all the time you will almost certainly take some life off the car. But SPORT mode won't do that unless you have a really heavy foot. You'll get 1000-1500 higher RPM over NORMAL mode before the computer upshifts under normal acceleration, and the computer will hold a givenRPM longer before upshifting. I can't see those differences as a significant source of wear. What it WILL impact is your fuel economy. Higher RPMs and faster acceleration use more gas--you cannot bypass physics. There is also the matter of cylinder deactivation. I don't know if that feature is active in SPORT mode.

Keep in mind, you can teach yourself to drive the car in SPORT mode so that it accelerates and upshifts almost the same as in NORMAL mode, you just have to be very precise with the accelerator pedal. You will have to use much smaller pedal movements while cruising if you don't want the computer to downshift. It can be done, but the juice might not be worth the squeeze.

 

[PonyDriver43]

Thank you Mark S. for you detailed explanation. The condition OP mentioned is the thing I dislike most about my BS/OB. Mine is mostly an in town daily driver and that is extremely annoying to me. In heavy traffic or store parking lots I really try to remember to twist to SPORT mode. If I forget my BS is real quick to remind me I forgot. Also have seen “turbo flutter” mentioned. ( not really sure exactly what/how that happens).

 

[Mark S.]

Thank you Mark S. for you detailed explanation.

You're welcome.

Also have seen “turbo flutter” mentioned. ( not really sure exactly what/how that happens).

I believe the poster who mentioned that was thinking of a different phenomenon. The problem we are discussing here occurs at low RPM with the engine under low-to-moderate boost. Turbo flutter occurs when the turbocharger is at peak boost and the driver abruptly closes the throttle. The video below is an example of turbo flutter, which is more accurately called compressor surge. You'll hear it every time the driver closes the throttle (foot off the accelerator pedal) to change gear, or to slow down.




FYI, turbo flutter is not particularly good for turbocharger longevity, which is why Ford (as well as most other modern engine manufacturers) took measures to avoid it. Take a look at the diagram below. Start at the air filter and follow the air flow to the cylinder. Just before the cylinder you can see the throttle. Imagine the engine is revving at a high RPM and the air going into the cylinder is fully pressurized (high boost) and you take your foot off the accelerator pedal. Where does all that highly pressurized air go? In the video above, the air is getting forced backward through the spinning compressor. The compressor blades chopping through that pressurized air is the sound you hear (flutter).

In the diagram between the compressor and the intercooler you can see a device incorrectly labeled "blowoff valve." Different manufactures call them by different names (recirculation valve, diverter valve, etc.) but their purpose is the same: to provide an escape for pressurized air trapped between the closed throttle and the compressor. A blowoff valve vents the pressurized air directly to the atmosphere, generating a distinctive "PSSSSSSH" sound which some like. In the diagram you can see the air exiting the (mislabeled) blowoff valve is routed back to the unpressurized side of the air intake system. That means this isn't really a blowoff valve, it's a recirculation or diverter valve.

In the diagram you see a small tube between the recirculation valve and the intake manifold. This is how the recirc valve is actuated in a purely mechanical system. With the engine operating at high RPM you will create a vacuum in the intake manifold when you close the throttle. That vacuum pulls a mechanically actuated recirc valve open.

The 2.0L engines incorporate an electronically actuated recirculation valve—the powertrain control module controls it. I'm not sure how Ford set up the 1.5L engines, but I assume there is a recirc valve somewhere in the system.

 

[Ford Motor Company]

Hello All,

Recently took in my 2022 Bronco Sport Big Bend (1.5L) as I felt some lugging/vibrations when trying to accelerate at around 1.5k RPM at Normal or Eco drive modes. The dealer was able to recreate it on my car as well as another one they had on stock and provided me with SSM 50530 and said it was normal. It seems like there really isn't anything they can do to mitigate the problem other than changing to Sport Mode.

Can anyone explain to me what is causing this issue? The way they explained it was not very clear. In addition, I can understand it is "normal", but what are the potential prolonged issues this may cause? I assume vibrations at any degree isn't really good in the long term.

Hey there. Can you please send over a private message with your VIN and the name/location of your local Ford dealer? I would like to take a closer look at your vibration concerns.

 

[PonyDriver43]

You're welcome.


I believe the poster who mentioned that was thinking of a different phenomenon. The problem we are discussing here occurs at low RPM with the engine under low-to-moderate boost. Turbo flutter occurs when the turbocharger is at peak boost and the driver abruptly closes the throttle. The video below is an example of turbo flutter, which is more accurately called compressor surge. You'll hear it every time the driver closes the throttle (foot off the accelerator pedal) to change gear, or to slow down.




FYI, turbo flutter is not particularly good for turbocharger longevity, which is why Ford (as well as most other modern engine manufacturers) took measures to avoid it. Take a look at the diagram below. Start at the air filter and follow the air flow to the cylinder. Just before the cylinder you can see the throttle. Imagine the engine is revving at a high RPM and the air going into the cylinder is fully pressurized (high boost) and you take your foot off the accelerator pedal. Where does all that highly pressurized air go? In the video above, the air is getting forced backward through the spinning compressor. The compressor blades chopping through that pressurized air is the sound you hear (flutter).

In the diagram between the compressor and the intercooler you can see a device incorrectly labeled "blowoff valve." Different manufactures call them by different names (recirculation valve, diverter valve, etc.) but their purpose is the same: to provide an escape for pressurized air trapped between the closed throttle and the compressor. A blowoff valve vents the pressurized air directly to the atmosphere, generating a distinctive "PSSSSSSH" sound which some like. In the diagram you can see the air exiting the (mislabeled) blowoff valve is routed back to the unpressurized side of the air intake system. That means this isn't really a blowoff valve, it's a recirculation or diverter valve.

In the diagram you see a small tube between the recirculation valve and the intake manifold. This is how the recirc valve is actuated in a purely mechanical system. With the engine operating at high RPM you will create a vacuum in the intake manifold when you close the throttle. That vacuum pulls a mechanically actuated recirc valve open.

The 2.0L engines incorporate an electronically actuated recirculation valve—the powertrain control module controls it. I'm not sure how Ford set up the 1.5L engines, but I assume there is a recirc valve somewhere in the system.

Mark S,
Thank you once again for the very revealing explanation. I'm not experiencing this phenomenon.
The one the OP referred to sure is annoying though.

 

[Blue oval fan]

My old Escape 1.5 seemed to do this worse than the BS. While the BS still does it, it is not as noticeable. Normal mode needs to be a happy medium. Sport can be a little too aggressive, and Eco is pretty much useless. Between Eco and Normal, there isn't a whole ton of difference other than Eco takes more pedal to get it to change gears to accelerate. I have tried both under similar conditions and the fuel savings isn't even noticeable. No need to be in such a low gear cruising at 40mph. But when in Sport mode the throttle response, RPM hang is a bit much. Ford could fix all of this with a simple ECU flash.

 

[ilpz365]

Generally speaking, heavy lugging is not a good thing to do to an engine. The kind of lugging I'm talking about is prolonged and/or frequent wide-open throttle at low RPM. It appears the computer in your car will not let that happen. Clearly, it allows a certain amount of increased power demand before downshifting, but theoretically Ford's engineers programmed it to downshift before you can hurt the engine.

Driving in SPORT mode simply remaps the shift point and throttle response. Throttle response is how much power you get vs accelerator pedal position. In SPORT mode you get more power with less pedal movement. You cannot demand more power than the engine is capable of producing, so throttle response is not a significant factor in engine wear. All things being equal, higher RPM does increase wear, so the fact the computer allows the engine to get to a higher RPM before upshifting will increase wear over NORMAL mode. How much? My educated guess is not significantly. If you drive it like Racer Rob, allowing the engine to wind up to redline or near redline all the time you will almost certainly take some life off the car. But SPORT mode won't do that unless you have a really heavy foot. You'll get 1000-1500 higher RPM over NORMAL mode before the computer upshifts under normal acceleration, and the computer will hold a givenRPM longer before upshifting. I can't see those differences as a significant source of wear. What it WILL impact is your fuel economy. Higher RPMs and faster acceleration use more gas--you cannot bypass physics. There is also the matter of cylinder deactivation. I don't know if that feature is active in SPORT mode.

Keep in mind, you can teach yourself to drive the car in SPORT mode so that it accelerates and upshifts almost the same as in NORMAL mode, you just have to be very precise with the accelerator pedal. You will have to use much smaller pedal movements while cruising if you don't want the computer to downshift. It can be done, but the juice might not be worth the squeeze.

does this happen with all 2022 BS BB? mine is doing this, its shuddering at 5-10pm, 15-20pm, 30-35pm

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