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Discussion Starter #1
Hi all. I have a 2009 Impreza Outback Sport that is doing an immediate stall in reverse only. 180k. Head gaskets, valves, timing belt and wp all done when I bought the car at 174k. No other issues. Just did plugs and wires last month. Scheduled maintenance rn is fuel filter and trans and diff checks. The car idles in park and neutral and will drive forward just fine. No coughing or spluttering or misfire, just dies immediately in reverse. My fuel light is on rn, could it be a dirty injector issue? Any other suggestions that I can look into would be appreciated!
 

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I will assume the AT Temp light is not on or flashing at you. I suggest you get the car scanned by someone that can read the transmission module. There may be an issue with the trans where it's applying forward and reverse at the same time. It will be a valve body issue. Either a solenoid or spool valve is hanging up. Line pressure tests will tell you for sure.
 

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There may be an issue with the trans where it's applying forward and reverse at the same time. Either a solenoid or spool valve is hanging up.
I have a somewhat different take on this.

Like a MT, if for some reason two gears are selected at the same time, the transmission would probably lock up. But even if an automatic transmission itself were somehow locked, there's still the torque converter that should allow the engine to continue running. For the engine to stall, the TC would have to be locked.

Perhaps the transmission itself isn't in two gears at the same time. Instead, the TCC is being applied when R is selected. With the car stopped and the brakes on (as is normal when changing to/from R), that will cause the stall.

This might be determined with the car raised and the wheels free to turn. Engine running, move the gear selector to R. If the wheels turn in reverse, then the transmission isn't seized in R. Press down on the brake pedal to slow the wheels. If that causes the engine speed to dip a lot and eventually stall, the TCC is probably engaged.

This is a strange one . . . be very interested in figuring out or learning the cause.
 

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@plain OM
I get your point.

If the TCC is locked in R then it would follow that the TCC would be locked in D and the same end result would occur; engine stalls. Unless there is an issue with the harness or wiring in the trans, or an issue with the TCM that only locks the TCC when R is selected, then the TCC should be locked all the time resulting in a mechanical failure of the torque converter, or again, the valve body.

The car is running in forward gears and not stalling. What I'd like to know is if it's starting in 1st when put in D, or, is it starting in 2nd, or even 3rd? Planetary gear function relies on the role of the sun and drum rotation or braking. This is how the gears are determined. This is also how reverse comes into play.

Then you have the torque converter function. Is the car stalling as soon as R is set, or is it stalling during the attempt to move the car in R?

The torque converter is designed to lockup via the one way clutch. Trying to move the car when two opposing gears are running would stall the car when an attempt to move took place. It would brake the engine in similar fashion as holding the brakes and letting off the clutch.

Trans data from the TCM is necessary and pressure readings in conjunction will tell the tale.

I can think of no other reason the car would stall only in R than there is an issue with fluid flow to the clutch packs that engage forward and reverse. We can discount the 2/4 clutch. Unless it's stuck starting in 2nd.
 

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Discussion Starter #6
I did not mention AT, but the stall feels like an engine stall from a clutch. This is my first AT, ever, 3rd Subaru and yes, fully strange!

At first it was stalling only when I tried to move in R, foot off brake. The last time I started it it stalled as soon as I shifted. Doesn’t sound or feel like it’s starting in anything but first gear. Now that it’s been mentioned, it did get stuck in second last week when I tried to park, but that resolved itself after driving home that day.

I am also inclined to think fluid blockage as the car is due, and there have been no warning noises or any other weirdness from the trans.

That being an affordable first option, I’ll try a system flush. Thanks for the input, much appreciated and I’ll let y’all know how it goes!
 

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The torque converter is designed to lockup via the one way clutch. Trying to move the car when two opposing gears are running would stall the car when an attempt to move took place. It would brake the engine in similar fashion as holding the brakes and letting off the clutch.
There is a one-way clutch in TC that the stator runs on, but I'm not aware of a one-way clutch used for TCC lock-up in these transmissions. Lock-up is effected by a disc-type clutch (not unlike that in a MT) that's inside the TC case. The case is connected to the engine crankshaft; the clutch disk is splined to the turbine shaft (input to the transmission).

Whenever the engine is running, there's a constant flow of ATF from the ATF pump through the TC in order to provide cooling. The TCC is engaged/disengaged by changing the port through which ATF is delivered to the TC and therefore the direction of flow through the TC. In one direction the disc is held away from the TC case; in the other direction the disk is pressed against the case. When it's pressed against the case, it connects the engine directly to the transmission.

When the TCC is not engaged, the TC is a fluid coupling that allows the engine to turn when the wheels and the transmission gearing elements are stopped, as is the case when the transmission is in R or D (or in this case, both!) and the wheels aren't free to turn. I can understand the transmission being in two different gears at the same time, but not the engine stalling without a solid mechanical connection between the engine and transmission input, i.e., through the TC.
 

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I wasn't referring to a one way clutch for the TCC.

All converters have a stall speed built in that utilizes the one way clutch as well as fluid flow. This can be demonstrated using your car. Start it up and after it warms a bit put it in gear and hold the brake firmly while accelerating the engine. The engine will only speed up to a point, then no matter how far you push the accelerator, it increases no further. Doing this increases the engine load, heats up the trans fluid faster and the engine tends to run on the rich side as the computer is trying to manage what you are doing to get the car to move to no avail. The stall speeds on Subies are usually around 1800 rpm, some higher.

Maybe I can explain the engine stall effect another way. If I had a planetary set available I could demonstrate it. Effectually, if two opposing direction gears are working against each other, in this case reverse and any of the forward gears, it creates a situation where the torque that should be transferred to the output shaft is directed toward the engine. This "reversed torque" brakes the engine causing a stall.
 

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Are we stalled [pun] on semantics?

Start it up and after it warms a bit put it in gear and hold the brake firmly while accelerating the engine. The engine will only speed up to a point, then no matter how far you push the accelerator, it increases no further.
This is indeed what I understand torque converter "stall speed" and "stall test" are. It refers to the rpm difference in rotational speed between the input and output of the TC beyond which the engine cannot increase that number. The engine can't go any faster, but it's still running.

Effectually, if two opposing direction gears are working against each other, in this case reverse and any of the forward gears, it creates a situation where the torque that should be transferred to the output shaft is directed toward the engine. This "reversed torque" brakes the engine causing a stall.
In this "reversed torque" example, does "stall" mean the engine actually stops running (as in, "it stalled and I couldn't restart it"), or does it mean, as above, the engine can't go beyond a certain rpm?
 

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The engine is stalled as in OFF.

I've run into this some years back with one car and it necessitated a valve body replacement. The engine would always start right back up and run normal, until you put it in Reverse, then it would shut off again. I don't recall what the exact issue with the valve body was; whether a solenoid or a spool valve. Too long ago and too many cars.
 

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Discussion Starter #12
Hey all. So after a transmission flush there have been no issues. It’s shifting like butter, barely feel it. It had been a bit rough before. I’m assuming the previous owner never did this as it was quite dirty! The car did reverse out of the driveway after a 15 minute warm up on flush day, no it defs wasn’t anything mechanical.

Cheers for all the helpful responses!
 
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