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01 STS over-reving during WOT?


halfrican

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<_< During a couple of "rolling start" WOTs I have noticed that the transmission of my 01 STS doesn't always seem to shift before the PCM appears to engage the rev-limiter. Normally the transmission appears to shift at or around 6000 to 6500 RPM, but occasionally seems to allow the engine to rev to almost 7000 rpm. During these instances, the engine seems to "lurch/cut-out" in a way that would indicate that the PCM is enabling the "rev-limiter".

Most of the time this does not occur, in fact the only time I have noticed it is if I go WOT from a rolling start (1st gear) as opposed to second or third gear.

I have checked the DTC for codes during these occasions with no results current or history.

Anyone else experience this type of "late-shift" with their vehicles? Is this something to be concerned with?

Another issue with the transmission what I have noticed is that if I shift out of park too quickly after the vehicle is started (only on cold start while engine is a high idle) the shift into reverse or drive is very "harsh". Brought up this concern with my dealer, they indicated that they found no problem and that when the trans/engine is cold this can be considered normal. Again, no codes present or history.

Thanks again in advance,

Half

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Half, likely what you're feeling at or near 7000 rpm is the rev limiter.

I agree with the dealer. When your engine idle is high, it will be harsh going into gear. Kind of like putting your foot on the gas, holding the idle high, and dropping it into gear. Like a very mild "neutral drop". It probably doesn't hurt the transmission when the engine is at high idle, but it'd probably be a smoother engagement if you let the idle settle down just a bit.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Half, likely what you're feeling at or near 7000 rpm is the rev limiter.

I agree with the dealer. When your engine idle is high, it will be harsh going into gear. Kind of like putting your foot on the gas, holding the idle high, and dropping it into gear. Like a very mild "neutral drop". It probably doesn't hurt the transmission when the engine is at high idle, but it'd probably be a smoother engagement if you let the idle settle down just a bit.

Jadcock,

Any reason why the transmission would be allowing the engine to rev so high? During these "over-revs" I am leaving the transmission in "drive" as opposed to "1 or 2".

Thanks for clarification on the "harsh" cold shift, I was hoping that it was just a reality of the fact that the N* have quite a bit of torque even at the low RPM (1200 to 1500) cold idle point.

Half

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Half,

As far as I can determine, the 4T80E transmission has no mechanical governor. All shift points are controlled by the PCM.

There could be several reasons for the "late shift". Among them are an inoperative/defective transaxle pressure switch or a sticking pressure regulator boost valve.

How many miles on your trans fluid? You may get some relief by simply draining the fluid and replacing the scavenge pickup filters.

Britt

Britt
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