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Over the winter I installed a Jake's D1 Transbrake and after buttoning a few things up, I finally took the car for a spin. All seemed to be going well until I hit a stoplight and the trans randomly lost all pressure. In a panic I rev-ed up the engine and it snapped back to life. This happened several more times, and eventually went away after about 15 mins.
Very occasionally the same thing would happen before the rebuild so I also installed a Sonnax actuator limit repair kit as well. (part trg-t48-act-tl)
The transmissions is wired for full manual with the EPC modified to allow fluid bypass. So I do not believe it's possible for this to be a tuning issue. When rebuilding I noted that my pump as some wear on the gears but didn't appear to be enough to warrant total replacement. I'm posting an HpTuners VCM Scanner log file to help illustrate. You can see the pressure take a full nose dive for seemingly no reason at all. This just a short startup in my garage moving through the gears.
Fluid level is reading just above the lip of pan which is right were it should be according to what I've read.
That's not actual pressure.
The 4l80e doesn't have a pressure sensor
did you add an aftermarket sensor then tie that into the stock ecu then name it trans pressure?
I doubt it
That is commanded control pressure. AKA the pressure the ecu targets in the AFL circuit by controlling the PCS
dropping to 0 at a stoplight is super normal. The trans doens't need any pressure at a stop light, so the computer lowers pressure to keep everything from wearing out.
If you watch PCS amperage. When the pressure you have highlighted is 0...the PCS amperage will likely be around 1 amp
when pressure you are watching goes to around 90...pcs amperage will be .1amp
did you add an aftermarket sensor then tie that into the stock ecu then name it trans pressure?
Yes, I really did permanently wire an electronic pressure sensor to the ECU and configured it to log as Trans PSI in my scanner. I poached the engine's EGR signal to do so and spent quit a bit of time calibrating it. I'm building this car for Drag Week and plan to keep a close eye on my scanner.
Regarding the PCS. The trans brake instructions call for completely bypassing solenoid by grinding down the sides. I should be getting full line pressure at all times. This is most visible in a similar set of instructions. The trans really is uncontrolled by the ECU at this point. http://www.jakesperformance.com/wp-c...s-08302016.pdf
I was looking through other logs last night and noticed this seems to happen most often when abruptly taking my foot off the gas. I removed most of the throttle follower tuning which causes the engine to return to a low rpm very quickly. I suspect the pressure dips and either the Boost Valve or Accumulator Limit Valve get stuck. Stomping hard on the gas seems to un-stuck it. How all these valve play together in order to manage pressure is a little beyond me. Seems as if it might be possible to pinpoint one of them.
Is there a chance my torque converter is done? Would a failing converter need to be "rev-ed up" in order to grab again?
OK,
If you actually have a sensor...is there a reason the pressure there is only 60-80 psi across the board in that log?
If the white trace is line pressure...I don't see it ever getting over 100psi
That's a problem on its own if you have bypassed the PCS
OK, If you actually have a sensor...is there a reason the pressure there is only 60-80 psi across the board in that log?
This was a short test in the garage. I simply stated the car, put it in reverse and drive, crept forward and back a few times. I think I could post a log today from a longer drive to get more readings at cruse. Hopefully I don't end up stuck somewhere.
thats its getting any gears at all with a "zero psi" line pressure seems really suspect. verify that pressure sensor isnt toasted. I use the $20 china ones and there at least one dud in every 5 i buy.
I'd say either
A. you have a massive issue
B. your sensor is wrong
C. you are way way low on fluid
in any range...park/rev/fwd...with fixed line
at 1500+ rpm...which it appears the red trace hit more than once...you should have 150+ psi with a stock boost/pressure regulator spring and even higher with aftermarket boost valves and springs
When getting a new pump, be sure to get a compatible pump. there are different changes and versions that will only work with certain years.
Here's an article that should help https://www.transgo.org/demo/06-177-...20matching.pdf
Well.. I was able to get a pump locally and pulled an all nighter getting the trans back in the car. Took it for a test drive this evening and it appears we are back in business. I'm getting about 130psi in park, and that's with a stock pressure regulator.
Posting the log here for those that are interested.
I pulled the transmission last night. The pump gear is badly damaged from an improper torque converter install..
We see that often. Even from well respected performance shops and experienced installers. The reason is the 4L80E is a little different on converter install than a TH400, PG, or 4L60E. I have videos discussing it on YouTube and we have very specific warranty requirements for our units that require pics be taken and sent in. If its not done. we don't even consider any warranty for pump failure.
4L80E Random Fluid Pressure Loss 
