Odd "boost" in engine at a specific RPM

[CurseTheSky]

The car is a 2003 Chevy Malibu with a 3.1L V6 and a 4-speed automatic. Nothing special, but it has a decent amount of torque and horsepower. While you can feel the torque off the line, it really lacks low end power. You don't get much out of it until 3-3.5k RPMs. First gear is somewhat short and accelerates quickly, while second gear is much longer (second tops out somewhere around 80MPH).

Around certain turns, I regularly get caught in second gear at low RPMs, which really shows the horrible low-end power of the car. I can keep my foot just about to the floor at 2k in second, and it feels like I'm driving a Geo. However, as soon as it (slowly) climbs up to about 3k, the engine gets a sudden burst of power. It's not a gradual "RPM goes up, horsepower goes up," it's a very obvious jump, always around the same mark. It's like changing from an I4 to a V6 right before my eyes.

It doesn't really bother me, but I've always wanted to know what causes this - my bet is on some kind of sensor or the computer, but who knows. The information is probably too vague, but I figured I'd give it a shot anyway.

Edit: I should mention, I've driven more than one of these cars. I've driven this way FAR more than any other, but they all seem to behave similarly. I don't think it's as simple as a clogged air cleaner / throttle body, or a bad sensor - I think it's something about the way they're designed. It's just odd.

 

[Jahee]

Maybe something to do with the torque converter? Not sure though i don't know automatics..

 

[Fenixgoon]

hitting the torque band?

 

[woodie1]

That particular RPM is probably when the engine starts to use the cam to produce peak torque. Nowadays most engines have a device to vary the cam/crank relationship at different RPMs so the torque curve is flatter.

 

[nwfsnake]

Feel free to stick a yellow stripe/VTEC/Type R sticker on it! :thumbsup:

 

[GoatMonkey]

Have you tried putting it into a gear manually, like selecting the 2 or something to make sure you're in that gear? It sounds like a transmission issue to me.

 

[dustmann]

Different gearing and engine setups cause power to hit in different spots. Envision a power curve on a dyno chart, yours sounds like it peaks more in the middle. Nothing to worry about, actually sounds like a bit more fun. Flat, broad powerbands are nice, but I like a car to throw my head back a little bit.

 

[Demon-Xanth]

You're not describing a downshift into a lower gear, correct?

 

[fbrdphreak]

Possibly has to do with the 2nd gear ratio. 4-speed auto + Malibu = geared for economy, not performance. If you're caught in the low RPM band of 2nd gear, you're likely just in a terrible spot of the gear for accelerating.

It looks like this is your transmission:
http://en.wikipedia.org/wiki/GM_4T40-E_transmission

It goes from a 2.95 1st gear ratio to a 1.62 in 2nd gear. That's a pretty steep drop. At low RPM, it would not surprise me that it takes a while to get moving. The engine itself is fairly torquey, I had an earlier version of the 3.1L in my 95 Grand Prix. In fact, the gear ratios are near the same as in your car and the 95 3.1L made less power - so I know what you mean. Although my tranny wouldn't crap around at the bottom of 2nd gear. You may consider resetting the ECM & TCM (pull the battery, let it sit for a while, plug back in) and it will re-learn your driving patterns. Might help learn when to downshift

Lesson learned: stop grandma-ing around and save 2nd gear for the higher RPM's

Seriously though, if you're getting proper gas mileage, no weird noises, check your tranny fluid (should be a pinkish red color, if it is dark that's bad), then likely there's nothing wrong.

 

[drpootums]

I notice this in my Oldsmobile. I have the 3.8 and the 4-speed auto and there are parts on the powerband where it's like "whoa, where did that come from!?!??!". My transmission is geared for economy/smooth & quiet cruising, and there are points where the power is pretty low and then all of a sudden it's like the engine is waking up. I don't think there's anything wrong with the car or anything, and it's even kind of fun to play around with.

EDIT: I should mention, it happens around 3000 rpm in my olds too, in second gear. In OD something similar happens when speeding up from 55-70 ish, but nowhere near the same effect as in second gear (and I don't mean it speeds up fast in OD, just faster than before 55 in OD)