Could use some help diagnosing high pressures and hard shifts on a fresh 4L80e. Transmission was built by Extreme Automatics. I reached out, but haven’t heard back after a few days.

I drove the car (recent L92/LSA swapped Buick Roadmaster) for the first time last week. Just a short drive back from the exhaust fabricator to my house; about 6 miles.

It was stop and go traffic for most of the way, and I maybe hit 45 mph momentarily. The transmission was clearly shifting very hard even under very light acceleration. Took me about 40 minutes and the temp climbed to 230+ as read by the ECM.

I finally had the chance to put a gauge on it early this week.



185 psi cold/park

160 psi warm/park

160 psi reverse

160 psi neutral

125 psi in all forward gears


Pressure will very briefly drop to 70-80 psi when moving the gear selector; for maybe 1 second.

I’ve had the pan off twice. Once to verify level on my Lokar dipstick. I pulled it off a second time because the electrical connector was leaking. Unfortunately, the new connector is leaking too but not as bad.

No DTCs. Here’s a short video with some HPTuners PIDS. https://youtu.be/Heb6TQ20JnQ?si=J__eE1_WmaFVYQjs

Anyway, I’ve got very little familiarity with auto transmissions. Any advice on how to work through this diagnosis would be appreciated.

 

Ok first and I do not see the video , Look at the current to the PCS . Does it vary with the throttle? Should go down as throttle opens and up when closing.
If it does this then I would try changing the PCS . You should be seeing a physical variance in pressure with throttle position which obviously is not happening. Provided the current is varying. The PCS would be suspect, Many do not change this during builds nor test them. I am actually working on a test device and figuring out calibrations. But if you have the current variance I would change it first.

 

Hey thanks for the reply. I just logged EPC amperage with the car on stands in the garage.

If I brake-stand while in gear and hit the accelerator, amperage drops from 0.88 A to about 0.10 A. Seemingly normal.

But...if I let off the brake and the output shaft spins, the EPC briefly and barely drops to 0.77 A and will even increase to 1.05 A.

Line pressures are the same under both scenarios.

 

Ok the line pressure not changing at all . Points to a bad PCS (EPC) or a stuck AFL or a STUCK Pressure regulator valve. In that order of likely hood .
So I would change the PCS (EPC) first. as it is most likely culprit and simplest to change,
The issue with a build unit is going to be which on unless you remember. It is the large sol at front, Does it have a large flat blade connector or a small plug type .

THIS -
OR THIS -

 

You're the man, Frank. Hopefully can knock it out this weekend and report back.

 

Welp, I swapped the PCS (which seemed ok visually, but who knows) with a new one and my pressures haven't changed. One kind of weird thing - the PCS/EPC arrived in what looked like a sealed GM parts bag, but it was oily as if the new PCS previously had fluid in it? Anyone know if that's how they ship, or should it be completely dry? I'm wondering if I got a used solenoid...

I also installed a new (second) internal wire harness, so that leaking is fixed for now.

Plus I added a new issue. The trans will no longer engage any forward or reverse gear. The gear selector moves, and I see the line pressure "blip" down a bit for each gear change, but the output shaft never moves. Pressures are still in the 160-180psi range in all positions.

 

No engagement at all with pressure and needle motion as you move through positions. INPUT SHAFT or CONVERTER would be best guess. But certainly internal

 

Damn. Just weird that it went from full engagement and shifting with high line pressures to no output shaft movement when all that’s happened in the meantime is a new internal wire harness and a solenoid.

I’ll probably drop the pan again just to take a look, but I’d wager I’m out of my depth so I guess it’s time to strap it to a pallet and send it back to Extreme Automatics.

So much for having this thing on the road by May lol

 

Well, I might've overreacted. I just went outside and moved the gear selector and then tried to rotate the rear wheels (on stands). Wheels won't turn in any gear.

I had to removed the parking pawl retaining plate to change out the wire harness. I'm guessing something didn't go back together correctly, and now it's not shifting out of park. Heading out of town for a week, so it'll be a minute before I can dig back into it.

 

through my conversations with the guys at EA, I was under the impression they use a single stage pressure regulator (ie,no boost valve or EPS regulation) in every unit they sell. Its a rock solid set up and I use their pressure regulator in all my high power and transbrake units. You have a couple options if thats the case. I would lower the overall pressure via the shim stack in the pressure regulator/boost valve delete assembly. consider replacing the separator plate with one that keeps the accumulator valve train and smaller shift orifices as i think they also use a HD separator plate that deletes the ACV.

 

You are 100% correct.

I got back in town and talked with them and this was confirmed. That's too bad. Looks like a poorly informed purchase on my part since this car will serve as a road trip vehicle and will need gentle street manners when called for.

Looks like I have some homework to do. I'm not particularly familiar with the voodoo of automatic transmissions (why I bought a built unit to begin with), but maybe I'll educate myself this winter and make this a goal for springtime vacations.

Thanks for the heads-up.

In the meantime, are there any TCC or other tuning considerations I should be mindful of for a static pressure setup such as mine? This mystery pushed back my dyno session, but I should be able to work in a session soon, and I'll want to make sure my transmission tuning is appropriate for how EA has set mine up...

 

Ah unknown variable. one of the reasons I refrain most times from doing Tech support for other companies stuff as I do not know the methods they use to do various things.
But yes for your application this will offer some unique challenges to get where you want to be. Good Luck.

 

I would eliminate any TCC PWM. Have it function like an on/off switch. The TCC slip may be the cause of the high temperatures you are seeing. 100*F over ambient is what the borg warner rep told me at the ATRA tradeshow.