408 LS with 4L85E Supermatic seems to "push through brakes" at idle when hot

I have a 408" LS with a GMPP 4L85E Supermatic transmission (E38 engine controller and T42 trans controller) that seems to want to push through the brakes at idle when the truck is warm. The transmission is stock (other than vasco input shaft, deep alum pan, large ext cooler) and I have a lockup torque converter. When cold, the trans shifts ok. After the truck warms up, it becomes difficult to keep it stopped a light. The engine doesn't seem to idle down properly and the trans seems "locked". It wants to push through the brakes. I have to shift it into neutral to keep t from rolling through the intersection. Once shifted into neutral, the engine seems to idle down properly. As soon as I put into drive, it wants to push through the brakes again.

Not sure f it is mechanical or something in the engine/transmission tune. I don't have a log file just yet. Hoping for some general advice or maybe that someone will spot an obvious flaw in the tune -see attached.

408 LS, HiRam, 102 Nick Williams DBW TB, 235/239 and .610/.610 cam, 88mm turbo @ 14 pounds, 4L85E, Pro Torque 4500 lockup torque converter, 9 inch, 4.11 gears with 32 inch tall tires.

If all of your vacuum leaks are fixed and your sure your converter is working correctly, then you can try lowering the brake and modifying some of your idle settings... That's if it's just not returning to idle now? A high stall converter shouldn't be pulling at all much though?

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Originally Posted by GHuggins

If all of your vacuum leaks are fixed and your sure your converter is working correctly, then you can try lowering the brake and modifying some of your idle settings... That's if it's just not returning to idle now? A high stall converter shouldn't be pulling at all much though?

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I've done some reading on the subject. During that time, I stumbled upon https://www.sonnax.com/parts/1989-lu...egulator-valve . Sonnax says it "Prevents converter or pump drainback, Improves converter release pressure, and Prevents engine surge at idle in'99-later vehicles" which seems to perfectly describe my problem.

I'm thinking of installing this part plus their line pressure booster valve and spring https://www.sonnax.com/parts/2170-li...re-booster-kit.

Does anybody have experience with these parts?

Nice to see you back online GHuggins.

I've definitely heard of issues keeping the converter clutch disengaged at idle on the 4l80e, and that there is more than one fix, and that sounds like one of them.
Sonnax is a well known company

anyways maybe this is similar issue from 4l80e
https://ls1tech.com/forums/automatic...l#post18371882

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The problem is gone! Idles fine with the Sonnax valve installed. No amount of tuning would solve my problem. It took several days, and input from others, to figure out it was the TCC staying partially engaged, and this valve solved the problem. It may not help everyone, but it made my life a lot more pleasant. Hope this helps others with the same problem. Now, all I need is a converter that is as loose as this one is supposed to be!

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Originally Posted by kingtal0n

I've definitely heard of issues keeping the converter clutch disengaged at idle on the 4l80e, and that there is more than one fix, and that sounds like one of them.
Sonnax is a well known company

anyways maybe this is similar issue from 4l80e
https://ls1tech.com/forums/automatic...l#post18371882

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Code P1810 set today. I am currently researching it. Does anybody have any experience with this code in a 4L85E? Is common? Are there certain things to look for? This seemed to happen infrequently with the prior converter but its actually setting the code with the new converter.

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Originally Posted by scottt28

Code P1810 set today. I am currently researching it. Does anybody have any experience with this code in a 4L85E? Is common? Are there certain things to look for? This seemed to happen infrequently with the prior converter but its actually setting the code with the new converter.

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I bought the Sonnax improved boost valve with the o rings around it (Part #34200-01K). I did not buy the stiffer spring. I also bought the line pressure regulator valve (Part #34200-14K) and installed it at the same time. A few weeks prior, I also replaced the pressure manifold switch. It continues to throw an 1810 code and goes into limp mode. The new parts (plus the new fluid and filter) certainly helped, but it still goes into limp mode.

Quote:

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Originally Posted by scottt28

I bought the Sonnax improved boost valve with the o rings around it (Part #34200-01K). I did not buy the stiffer spring. I also bought the line pressure regulator valve (Part #34200-14K) and installed it at the same time. A few weeks prior, I also replaced the pressure manifold switch. It continues to throw an 1810 code and goes into limp mode. The new parts (plus the new fluid and filter) certainly helped, but it still goes into limp mode.

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OK... update... you can check all of the wiring and the connectors. You can change the fluid and filter. The Sonnax valves absolutely helped things. You can install a ACDelco 24222077 GM Original Equipment Automatic Transmission Manual Valve Position Pressure Switch. Annnnnnnd you can check the various shift circuit solenoids with an ohm meter... BUT, unless you go into the Tools > Transmission section of the scanner software and command 2nd gear, you won't know if it clicks or not.

First gear... click.
Third gear... click.
Fourth gear... click.

Second gear... crickets.
Second gear again... nothing.
Annnnd again... nothing.
Second second second... no click. Not a click to be found. Clickless. Simply does not click.


In the absence of click, I have ordered the following:
ACDelco 24230288 GM Original Equipment Automatic Transmission 1-2 Shift Solenoid Valve
ACDelco 24230289 GM Original Equipment Automatic Transmission 1-2 and 3-4 Shift Solenoid Valve

Can't tell you how happy I am that all you guys pointed me toward the click checker.