4L80E shift to OD then engine RPM flare - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-06-2010, 05:07 PM
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4L80E shift to OD then engine RPM flare

My bddy is finishing up a 31 model A w/ a blown BBC (about 850 HP) and a 4L80E. He has a TCI computer controller. We programed in all the parameters for the computer an it's shifting pretty good 1-2-3, but when it goes into overdrive, it only holds for a second and then it the RPMs flare up like it's in neutral. He immediatly lets off the gas so as to not cause any damage. The transmission was professionally rebuilt by a local shop and this is the first time it's been run. It took 14 quarts of fluid and was run on jack stands at first to get the fluid circulatiing. The computer shows everything working correctly, but you can see the RPM flare after the shift into 4th. You can see in the log file that the RPM's drop as 4th engages, but then flares up after a second or so.

Any help would be apprciated.

Here is a log file of the TCI:


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Old 09-06-2010, 06:27 PM
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Most complaints in an OEM application with weak or drop out of O-Drive is shift solenoid "A"

were shift solenoids replaced?
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Old 09-06-2010, 08:16 PM
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I'm not sure if they were replaced. I did some more research and went over and just tested the ohm reading for the shift solinoids and the force motor and they checked out.

Can you tell me the solinoid sequence for shifting?

One thing we found was the TCC wire on the TCI computer was not hooked up and the TCC wire on the harness was cut. I'm wondering if the transmission builder gave him a non lockup converter and cut the wire in the harness.

The other thing I'm seeing in the data log is about 1 second after the OD shift, there is a voltage drop, like some thing is being energized (TCC maybe?)and then poof, the RPM's flare up.
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Old 09-06-2010, 08:43 PM
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solenoids fail in two different methods; electrically and hydraulically.

they can test fine electrically and fail hydraulic test.

shift sequence is;

electrical applied = "on" which means pressure is held

1st = A on, B off

2nd = both off

3rd = B on

4th = both on ... if "A" does not hold, the trans drops to third.

Lock up problems can be from the TCC solenoid to pump stator bushings, sealing ring on stator



Pump requires mods to properly run a non lock up converter

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Old 09-07-2010, 07:22 AM
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Thanks for the info, I'm not sure what the builder did. I'm thinking he should replace all the solinoids and sensors to be on the safe side. We already found the speed sensor to be bad.

I'm also wondering if I should increase the line pressure in all the gears to accomdate the TQ of this engine.
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Old 10-19-2010, 10:23 AM
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Update:

Replace the solinoids and the trans shift fine now. Glad it wasn't something internal.

Thanks Crosley
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