Sounds Like Tire Slipping/fixed

[KentuckyC]

'21 BB, all recalls done. May not be 'cause and effect' but after the battery recall, now at 30mph or so, if I let off throttle quick, there is a brief half second sound like tires are slipping on a wet surface. Do have the brake release cable rattle, which dealership says is 'normal' ( know about fix, but try to convince them). No visible marks on driveshaft, no front axel looseness.
Dealer tried to blame slip it on new slotted rotor, but those have been on for 500 miles. Said" nothing we can do, but we put it on record you came in".
Anyone else have the slip noise? Can say transmission shift is normal up and down.
FOUND AND FIXED. Issue was pinpointed to turbo system. When quick drop of throttle at high Rpm s, the compressed air gets trapped between compression vanes and throttle plate. Valve dumps it into intake. Dealer found that air filter in housing was not seated and when pressure vented into intake it caused filter to lift and flutter from pressure. Dealer was good and since it was caused in last The Works service, no charge to fix and free Works the next time needed. That's good service Tim Short Ford!

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[thomasm23]

I get a “chirp” sound sometimes from under the hood. It could be coming from the design of the accessory drive belt. This belt does not have a traditional spring tensioner. The belt stretches around the pulleys to create the correct amount of tension.

 

[prissychrissy72]

My slip is in drive not breaking.
they haven’t told me why yet.

 

[KentuckyC]

Tried lowering tire pressure for more traction, used belt conditioner on accessory belt, still no change. Pirelli Scorpion tires are still well within specs.
Anyone know if there are transmission issues if computer will throw a code, at least if I know that, I will just not have to worry ?

 

[thomasm23]

Found this online..

Also referred to as turbo bark or chirp, compressor surge occurs when intake air actually reverts back out of the compressor. It’s most often experienced when elevated boost is produced and then cut off abruptly (i.e., you lift off the throttle suddenly). The noise you hear is the compressed air trapped in the intake that has nowhere else to go but back out the way it entered the turbo. Surging is extremely hard on the compressor end of the turbo, and prolonged surging will eventually beat the thrust bearing to death. Blow-off valves are commonly used in high-surge applications.

https://www.drivingline.com/articles/7-ways-to-kill-a-turbo-and-how-to-avoid-them/

 

[KentuckyC]

Found this online..

Also referred to as turbo bark or chirp, compressor surge occurs when intake air actually reverts back out of the compressor. It’s most often experienced when elevated boost is produced and then cut off abruptly (i.e., you lift off the throttle suddenly). The noise you hear is the compressed air trapped in the intake that has nowhere else to go but back out the way it entered the turbo. Surging is extremely hard on the compressor end of the turbo, and prolonged surging will eventually beat the thrust bearing to death. Blow-off valves are commonly used in high-surge applications.

https://www.drivingline.com/articles/7-ways-to-kill-a-turbo-and-how-to-avoid-them/

I think you are on to something here. Sound is in area of front end, though it was tires or FWD unit, but could not pinpoint location. This makes sense since it would be from motor area. Thanks very much for input.

 

[Mark S.]

Blow-off valves are commonly used in high-surge applications.

Both engines the Bronco Sport uses are equipped with recirculation valves. They work similarly to a blowoff valve in that they provide a place for pressurized air in the intake tract to go when you close the throttle, but instead of venting to atmosphere they recirculate the air back into the intake tract ahead of the turbocharger. It's possible OP is hearing the movement of air after the valve opens.

 

[KentuckyC]

Both engines the Bronco Sport uses are equipped with recirculation valves. They work similarly to a blowoff valve in that they provide a place for pressurized air in the intake tract to go when you close the throttle, but instead of venting to atmosphere they recirculate the air back into the intake tract ahead of the turbocharger. It's possible OP is hearing the movement of air after the valve opens.

Thanks, such information is valuable. With our modern engines and the technology in them, it's great that our forum gives us a means of understanding the unknown

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