2022 Violently Surging on Restart from Auto Stop/Start

[CableXJ]

It happens a few times a day in stop and go traffic. It’s quite violent. I thought I’d been rear-ended the first time it happened. Ford checked things out (unable to reproduce) and nothing in the computer. I’ve searched for info with no joy. Any ideas would be welcome.
72,000 kms.

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[thomasm23]

It happens a few times a day in stop and go traffic. It’s quite violent. I thought I’d been rear-ended the first time it happened. Ford checked things out (unable to reproduce) and nothing in the computer. I’ve searched for info with no joy. Any ideas would be welcome.
72,000 kms.

Could it be this?

https://www.broncosportforum.com/forum/threads/engine-mounts-replacement.13362/

 

[DWG]

Not sure if what you are describing is the exact same thing I had with a brand new 2023 Escape but with only a few hundred miles when I would take my foot off the brake after the engine shut down to start moving again the engine would start right up but there was a couple seconds delay before the transmission would engage and when it did it there would be a violent bang as it engaged. It started while stopped on a downward slope and then would just happen more often whenever stopped.

I was able to reproduce it for the dealer but they could never find the issue. In my case because the car was so new Ford bought it back but one thing that the Forman who drove with me mentioned was the the transmission has an internal auxiliary pump that pressurizes the fluid so the the auto start/stop reengages smoothly.

Try driving around in different situations to pinpoint when the issue happens and than drive wit the Forman at the Dealer to make sure you can duplicate the issue for him.

Here is a description of the system from a google search. It is an AI description so it may not be 100% accurate but I think it is good enough to understand the system:

Yes, the 8F35 transmission has an auxiliary pump and accumulator system to pressurize the fluid, primarily for use in conjunction with the engine start/stop system. This system ensures that the transmission is already pressurized when the engine restarts, eliminating any delay in gear engagement. The auxiliary pump, mounted on the transmission, supplies line pressure when the engine is off, while the main transmission pump has been modified to improve flow rates upon engine restart. The accumulator cushions shifts and helps to maintain pressure.

Here's a more detailed breakdown:

Auxiliary Pump:
.This pump, often mounted on the transmission, is responsible for maintaining pressure within the transmission when the engine is shut off, according to Gears Magazine and Transmission Digest.

Accumulator:
.These devices, typically located within the valve body, help to cushion shifts and maintain pressure within the transmission.

Engine Start/Stop System:
.The 8F35 transmission, along with other modern transmissions, is designed to work with engine start/stop systems. These systems shut down the engine at idle to improve fuel efficiency. The auxiliary pump and accumulator ensure the transmission is ready for quick engagement when the engine is restarted, according to Gears Magazine.

 

[BravoAlpha]

How about turning it off.

i turn mine off. I don’t trust the system

 

[Mark S.]

the transmission has an internal auxiliary pump that pressurizes the fluid so the the auto start/stop reengages smoothly.

This is almost certainly the right answer.

 

[CableXJ]

I’m coming to that conclusion as well. ?

 

[CableXJ]

Well, after having the tranny serviced and several weeks of bliss, the problem is back. So I guess I’m back to the dealership. I did mention the pump/accumulator thing so maybe they can fix it before something breaks.

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