trans premature shift

[burt ragio]

What would cause my transmission to all of a sudden start shifting prematurely ? It almost feels like I took the custom tune out. It even will detenate/ ping. Tried three tanks of hi test and it still happens.

[tbone]

The EPC solenoid. (?)

The electronic pressure control (EPC) transmission switch controls the EPC unit, which regulates the hydraulic pressure in your automatic transmission. This regulation allows the transmission to change its resistance levels when the engine begins to work harder. With greater pressure, the engine has to work harder to shift the gears, which prevents it from running up against its redline. Conversely, when the engine is under load, the pressure is reduced by the EPC so the engine works less on having to moving the transmission gears and can use its energy to move the load.

Read more : http://www.ehow.com/info_7752506_epc-transmission-switch-do.html

[chief455]

pinging = bad.
Can you flash the tune in just to see if it recovers?

[burt ragio]

These symptoms only happen under light load. Can the EPC be changed easily ? Is the EPC located external of the trans ?

[tbone]

Pull the trans pan. It is right there, and I believe you don't have to pull the valve body to remove and replace it. Not 100% sure though. Even if you do, not a difficult job.

Go to 3:35 in attached video.

https://www.youtube.com/watch?v=pPC7CwknaUM

[tbone]

Here you go. This is for a 92-97, but it shouldn't be much different, if at all. Don't get mad if this isn't the issue with your trans.

http://www.teckpak.com/teckfitz/products/pdf/solenoids/76923.pdf

[chief455]

Don't get mad if this isn't the issue with your trans.

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or your detonation.
May not be related issues, hopefully it is, and this fixes it :)

[mcb26]

Possible throttle position sensor. Easy enough to give it a try.