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5eat transmission slippage + no ECU/TCU diagnostic communications


dextr214

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Hey everyone, sad to say that my '05 LGT is in poor condition. I've tried searching for similar issues and the closest i can find is: http://legacygt.com/forums/showthread.php/5eat-gears-slipping-please-help-214805.html - which differs in the fact that his problem was only when the tranny shifted between 2/3rd gear.

Some background: The car is @ 160k miles and has been Stage 2 for ~100k miles. I've maintained the car myself and haven't, in the last 120k miles, taken it in to a shop for any sort of maintenance. I recently received a replacement Cobb AccessPort because my original stopped working. I installed the accessport with the Stage 2 91 octane map that Cobb includes - the same map i had previously been running for the last ~100k miles. After re-flashing, this problem showed up after ~200 miles of highway driving and ~50 miles of city driving. Let me know if more background info is helpful.

 

Last week, only a few days after re-flashing the ECU, I was on a 40 mph road and accelerated from a stop light at maybe 50% throttle when my RPMs started raising faster than my speed was increasing. I tried accelerating quickly at the next light and found that anytime i gave the car a large amount of throttle it would start slipping like this. Sport mode or not, slippage is about the same. It appears to occur during & after shifts. I can get slippage even long after a shift has occurred and driving appears normal by just giving it more throttle. Acceleration up an incline is almost impossible as simply maintaining 50mph on an incline is hard enough. A large vibration starts after its been slipping for a short period of time. Higher RPMs seem to be worse. Leading into the fact that accelerating from a stop isn't bad if you keep the throttle low enough for the RPMs to also remain low (under 3 or 4k). I also tried uninstalling my Cobb AP and everything was the same, the slippage & vibration.

 

With the AP uninstalled I took it to a Subaru dealer (Mike Shaw Subaru) in Westminster and after looking at it they said it needed a new transmission along with valve cover gaskets & rear diff seals. When i asked what was wrong with the transmission they only said "some sort of internal transmission failure" - so that's super helpful, i'm guessing they can tell just about as much as I can that there's a transmission problem and they also said that "any transmission problem requires us to replace the entire transmission because subaru won't let us work on them".

With the AP still uninstalled I then took the car to Finn Mototech in Broomfield. After talking to the owner, Rob, I learned that they couldn't communicate with my ECU/TCU through either of their three diagnostic computers. This confused me because the people at Mike Shaw didn't say they couldn't communicate with the ECU/TCU - made me think that they somehow locked it down knowing that i was going to get a second opinion. Anyway, Rob sent an email to Cobb asking if they had seen anything like this, partial contents: "I am trying to gain access through the OBD2 port with our diagnostic equipment but cannot access the engine or transmission but CAN access the SRS and ABS systems. To reiterate, we currently have no communications with the ECM/TCM systems through the factory interface." They replied that if the car had been restored to stock (AP uninstalled) then everything should be accessible - well, as mentioned above, the AP was already uninstalled. I asked Rob if they'd try re-installing the AP with the Stage 2 map and see if that somehow changed anything - same results. Unfortunately but understandably Rob doesn't want to work on the car until he can access the ECM/TCM to verify that after his work is complete, the problem has surely been resolved.

 

This is currently where i'm at - unsure what to do next. I'm wondering if a Subaru dealer would be best (maybe restore ECM/TCM comm) or if the local Super Rupair shop would be a good attempt. At this point moving the car to multiple shops during business hours is affecting my work schedule so i'm trying to make the best decision before spending the time to relocate my car.

 

All help would be VERY appreciated! Thanks everyone!

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I do not know how to say this any more clearly without adding in lots of extra words to make my point more substantial, so I underlined it :). Use your imagination to project that you just paid $1000 for the most advanced diagnostic service in the US to tell you the following summary (actually, you can paypal me $1000 or whatever amount you feel is reasonable for the explanation I've provided below; these posts take a long time to write, and time is money, especially for a mechanic). I underlined every important point. Everything else is irrelevant and excess. Here goes.

 

Your 5eat is worn out, and you either need to have it rebuilt or replaced. I'm surprised you made it to 160k miles with 100k miles of Stage 2. The lower torque of the Cobb OTS map is most likely what allowed your 5EAT to last so long without a valve body upgrade. I could waste a lot of time explaining to you what exactly has failed internally, how and why. Though that may be the most apparent question to you, in this specific situation it is also the most irrelevant. If you want to know which specific internal sub-system has failed, I can narrow it down for you to. Just tell me what gear(s) you were in when the slipping events occurred. However, that information will again be entirely irrelevant, since the practical solution is to replace the whole transmission, or replace all the clutch pack friction components and seals with new (aka transmission rebuild).

 

The Why:

The slipping started around the time of your Cobb AP swap because the accompanying ECU reset also causes a sort of TCU learning reset. Your 5EAT friction internals are so worn out that the only reason you could still get any gear ratio engagement and power holding is because the TCU adapted by significantly increasing line pressure and making other electronic output changes. Pretty clever TCU tuning by the engineers at Jatco, though any modern transmission should do this as well. When the TCU did its reset, the learning adaptation went back to base level of when the transmission was new. So then you had far less mechanical grip in the transmission. It will slowly learn to bump up pressure again, but it starts over each time you make a significant change with your accessport. When it slips, a lot of wear occurs very quickly. You're already at 96% worn out, ish, and now that is snowballing each time it slips.

 

Temporary hacks to get by for a little while longer:

If you want to keep it running as long as humanly possible without doing any rebuilding/replacement, you have the following options.

1) Keep it in sport mode, not regular. Manual mode is better, especially in 1st gear.

2a) Is your ATF fresh? If not, you can replace it with a correctly specified fluid. This might help, maybe.

2b) Add a bottle of Lucas Transmission Fix. This might be the band-aid that does the most for you vs just clean fluid. Your 5EAT is 96% worn out anyways, so one way or another it's coming out in the not-too-distant future. So you might as well try it.

3) Stop flashing your ECU. You need the TCU learning to get enough friction grip, and that can take hundreds of miles of regular driving and shifting to reestablish itself to the old levels.

X) Install an upgraded valve body. Except don't because it's crazy to do such a thing on a transmission this worn out. Epitome of throwing money down the drain. If you did, you would still likely have to take apart the valve body and clean it after the imminent failure, since when these 5EATs fail they puke a thick black friction residue absolutely everywhere; at least it's easy to clean once every single component is disassembled, if you have the right parts washer setup.

 

I hope this response is technical enough per what you were looking for. I can get far more technical and detailed, but again, irrelevant.

 

Out of curiosity, what exactly was your ATF maintenance procedure all these years? I'm pretty curious about this one.

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Wow, thanks ClimberD@HexMods! While waiting for responses I read up on your HexMods F1 and realized that i should have done that long ago - unfortunately i wasn't on this site much in the last few years...and its looking like thats probably why i didn't see the HexMods F1 before. Anyway, your post about the F1 also includes a question (Will a valve body modification help or improve a partially worn, damaged or slipping transmission?) that keyed me in on what you just detailed - TCU learning could have covered up this wear until my re-flash. This makes a lot of sense..now.

 

So aside from the transmission problems that you quite clearly lined out, do you have any idea why my tuner wouldn't be able to communicate with the ECU/TCU? One thing i left out in my original post is that the Cobb AP seems to work/communicate just fine - it can re-flash (which i'll stop doing) and view live monitoring data etc.

 

To answer your question about ATF maintenance let me try and remember what i've done. I'll verify this later but for now this is what i can recall. Missed 30k Flush & Drain, F&D @ ~60k, F&D @ ~100k, full tranny flush @ ~120k (i forgot but this actually was at a dealer), F&D @ 150k

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Nice, I was guessing you had done several fluid changes over the car's life since otherwise it should not have lasted anywhere near that long especially due to Stage 2, or even up to 160k miles without stage 2.

Since I have no details, my wild guess is that your tuner bought a bunch of scanners that just don't work well on your car. Some mechanics have a lot of brand loyalty or tool-type loyalty. That can be a bad thing in that you end up having 3 of a similar tool, and zero of the kind you need in rare instances. Many big $$$$ scanners still can't beat the factory dealership OEM scanners. All that said, I'm not an ECU communication or CAN communication expert, not even close. I would say ask someone who is, maybe on the RomRaider forums or Cobb forums, but 99% likelihood it's a complete waste of your time. Car works well, functions as designed, even beats the odds on 5eat lifespan. So perhaps cut your losses with trying to get answers to things that do not matter. The rabbit hole is bottomless. < people devote their lives to external knowledge, only to learn in the end that what they were really after was ultimately unknowable.

 

Sent from my HTC One X using Tapatalk now Free

[CENTER][B][I] Front Limited Slip Racing Differentials for the 5EAT now available for $1895 shipped, please inquire for details! [/I][/B][/CENTER]
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Fishbone I'm not trying to be argumentative, but for the reasons listed above, he should not touch or mess with the ECU / TCU until he gets a functional 5eat installed that has some or all of its "meat on the bones", or "tread on the tires". Currently his 5eat is equivalent to tires worn down to the wear bars, driveable, but not for long, and should be replaced ASAP in order to get back to being able to handle anything he can throw at it, such as ECU flashes, WOT, etc.
[CENTER][B][I] Front Limited Slip Racing Differentials for the 5EAT now available for $1895 shipped, please inquire for details! [/I][/B][/CENTER]
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If he's been driving regularly then the TCU would have relearned around the worn friction material. The AP is irrelevant. If the AP has any impact, it would most likely be related to scaling of certain tables, and would most likely only make a small difference to transmission output pressures. Most of it should be on the learning. Now that it's working (for the time being) he should not mess with it, unless he wants to demonstrate the slipping, which would be a complete waste of everyone's time since it's completely obvious what the problem is and especially how to fix it. I swear I'm about to unsubscribe from this thread :spin:
[CENTER][B][I] Front Limited Slip Racing Differentials for the 5EAT now available for $1895 shipped, please inquire for details! [/I][/B][/CENTER]
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1) Keep it in sport mode, not regular. Manual mode is better, especially in 1st gear.

 

Sorry to go on a tangent here, but I'm trying to learn more about this tranny and I have some questions. *raises hand*

 

1) What exactly about manual mode that would make it put less wear on the tranny?

 

2) (noob question alert) I noticed that in manual mode it's almost like there are these "half-gears" so say I'm cruising in 5th at 2500 RPM and suddenly I give it the beans, then it's able to quickly jump to a higher level of revs without actually downshifting. In other words, it acts like it's in 4th momentarily until I behave myself, but shows it's in 5th. What exactly is it doing?

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1) in manual mode the transmission uses the highest line pressure of the 3 modes of driving, therefore shifts are firmer and quicker

 

2) you are seeing the torque converter lock-up in action; when it's locked up, it gets rid of the inherend slopiness and feels like a direct, connected manual transmission and when unlocked it feels like, well, shit

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1) in manual mode the transmission uses the highest line pressure of the 3 modes of driving, therefore shifts are firmer and quicker

 

2) you are seeing the torque converter lock-up in action; when it's locked up, it gets rid of the inherend slopiness and feels like a direct, connected manual transmission and when unlocked it feels like, well, shit

 

So in other words, when I behave I'm actually driving in bitch mode. :p

 

I appreciate the explanation. Thanks.

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  • 2 weeks later...

The car is driving like normal but i've also been very delicate - granny driving until the tranny gets replaced. ECU/TCU comms have not been restored but the learning & resets do appear to follow the patterns that ClimberD@HexMods described.

The plan now is to save up for a low mileage tranny and keep the car. With the $1800 price tag on the parts+labor i don't think i'll be willing to pay another $500 for the valve body...although it does look like a great mod & that i'd like the difference in feel.

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It depends. You will read a lot of horror stories around here but with proper maintenance, meaning using a high quality synthetic oil with a proper change interval, as well as either removing or replacing the banjo bolt filters, there's no reason the stock turbo would not last.

Dropping the downpipe to inspect the turbo for shaft play is not hard and at your mileage I would do it just for peace of mine.

My LGT is at 107K miles, has been Stage 2 since 50K miles, the transmission is in top shape and so is the turbo.

I use 10w30 synthetic oil year round, have replaced the banjo bolt at 50K miles (it was spotless) and removed it altogether at 100K miles.

I have a modded valve body done by IPT (back in the day when it was the only game in town and therefore the shifting is not as quick and firm as the ones done now) and run Amsoil synthetic in the transmission, along with a TruCool 4452 trans cooler.

I've done brake-torque launches, have driven it hard on occasion but I have never beat on it.

Contrary to some sentiments on this board, this car can and does last. Mine and others are living proof of that.

Do not worry too much, just do some maintenance, take care of it and enjoy it!

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  • 2 weeks later...

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