RPM's Slightly Increasing Momentarily While In Overdrive?

[jlells01]

Something I've been wondering about with the '95 3.1L Lumina LS I'm driving is that while in overdrive, the RPM's will rise up (maybe 200 RPM's, or so) when the throttle is actuated after going down a hill, or when you get back on the throttle after having backed off of it for a second.

 

For example, when you get to the bottom of the grade, and start to go back up, and the pedal is depressed to maintain your speed (whether you are doing it yourself, or the cruise control is activated), the RPM's will momentarily increase, and then settle back where they should be at. Same thing happens on level surfaces when you back out of the throttle for a second, etc, and then speed back up.

 

Is this just a trait of these cars?

Is is the torque converter locking/unlocking?

 

Once again, thanks.

[94CutlassSLCoupe]

my '94 CS 3100 does the same thing...i always thought it was the lockup torque converter

[AWeb80]

I know exactly what your talkin about.

 

I think the tranny is just getting the car up to a speed it likes in order to lock in the torque converter....

 

 

someone correct me if i'm wrong.

[KrazyCutlass1995]

yea , my cutty does same thing ... all its doin is holdin rpm steady for a sec before the tc locks

[chadz34]

It SHOULD lower the RPM's. But I don't know, you never know with these cars.

[Crazy K]

It's the Torque Converter Cluth lock up. btw, if you held the brake on just slightly, it would disengage the TCC, if you repeated a known situation where this phenominom occurrs while holding the brake slightly depressed, You'd be able to compare the results.

 

also, I think if you are off the gas, but rolling at speed, the tcc sometimes releases(probably detecting the Throttle Position Sensor, throttle closed) and actually allows your engine to crank slower than the transmission is turning.

[GOT2B GM]

While you are coasting down the hill without any throttle, your torque converter unlocks, which isn't noticable. When you get back into the throttle at the bottom of the hill, the engine will the revving slightly higher for a second because the TC is unlocked. Then once the ECM decides that you have a steady throttle input (not accelerating or braking) it will lock up the TC for better fuel economy.

[jlells01]

I just haven't noticed it in other vehicles that I've driven...

[TeeJay3800]

It's definitely the TCC. When you let all the way off the gas, the TCC disengages and then has to reengage once you touch the gas again. I always found that annoying and I don't experience that in other cars. It's very noticeable on mine.

[99RegalGS]

Yep, It's the TCC. It's normal.

[jlells01]

I always found that annoying and I don't experience that in other cars. It's very noticeable on mine.

 

Ditto.

 

Why are these cars the exception?

[TeeJay3800]

I always found that annoying and I don't experience that in other cars. It's very noticeable on mine.

 

Ditto.

 

Why are these cars the exception?

I have know idea. I know its "normal", but on my parents knew cars (4T65-E's), I don't notice it at all! It's a mystery to me.

[94CutlassSLCoupe]

I chaulk it up to just the 4t60-e...mine shifts hard as a motherfucker from 1st to 2nd and the torque converter locks up pretty noticably too. My car has 39k and the original trans...shifts exactly at the correct point and the fluid looks new...lol

 

Weird how we have 4 other cars with the 4t60-e and they are nice smooth shifters...my old '88 with the 4t440 shifted like a bastard from 1-2 also

 

I'd much rather have the 282...once you drive one of these for a while, you don't want the auto back (and this car is a Quad 4 lol)

[Crazy K]

I chaulk it up to just the 4t60-e...mine shifts hard as a motherfucker from 1st to 2nd and the torque converter locks up pretty noticably too. My car has 39k and the original trans...shifts exactly at the correct point and the fluid looks new...lol

 

Sounds like you need some moderate trans work. My service manueal for a 1994 CS w 4t60e says a harsh shift from 1 to 2 can be caused by a few things.

Oil pressure too high or low.

Accumulator piston or valve sticking, or bad or misposition gasket on accumulatro piston, or a mislocated No. 2 check ball.

 

hopefully that might help?

[94CutlassSLCoupe]

I dunno...the shift isn't that bad, just stiffer than normal

 

either way it works just fine...so i'm leaving it alone

[Crazy K]

ok, just giving you what I info I had at hand. Investing in a trans service manual might not be a bad idea, and if you change your mind you might give it a once over next time you change your filter. -Ken