Piston Slap: The Kid's Got a Point, Dear

TTAC Commentator Silent Ricochet writes:

Hi Sajeev, I am the owner of a 2002 Chevrolet Cavalier Z24 (has the 2.4L LDR motor in it) with about 128,000 Miles on it. I being a teenager, have my fun with it, but also baby it when it’s cold out, let it warm up plenty, even in the summer, and give it an oil change every 3000 Miles; no excuses. The car has a 5-speed Manual Gearbox, and I’m trying to figure out this awful noise that comes from my car when shifting from time to time. In any gear, other than first, if the RPM’s are too low for that gear (usually under 2000 RPM), the engine is kinda sluggish (that’s expected). What isn’t expected is this weird metallic vibrating sound that comes out of my car. Happens often when being in too high of a gear when going around a turn (even in 2nd gear, and I can’t put the car in 1st around a turn unless I’m doing under like 5 MPH). Pressing the gas harder to raise my RPM’s quicker does nothing, if anything just amplifies the sound, so What I must do is either downshift to a lower gear if possible, or just lightly hold my foot on the gas until I get back into my Torque band around 2400RPM. The noise can be hear well outside of the car, as I get looks from people walking by when the noise is made, and I can even hear it reverberate off the houses in my neighborhood when my windows are down. What is this noise and is it a cause for concern?

Sajeev Answers:

Being a teenager with a hot-ish stick shift car, you like to “hoon” around, right? If so, today’s is your lucky day, because you’re getting the hot-rodder’s equivalent of money in the bank: a busted component that is cheaply replaced with a go-fast part.

Pretend you live in a stereotypical 1950s TV family sitcom; your (nuclear) family is sitting down at a sea foam green dinette set for dinner. Mashed Potatoes, beef and nothing made with high fructose corn syrup. You tell Mom and Dad about the “ruckus” you make in the neighborhood, and the fun and cheap fix for it. When mentioning the fix/performance upgrade, Mom frowns. Your little brother giggles. And Dad, with a slightly evil grin says, “the kid’s got a point, Dear.”

If the Z24 makes that much of a racket around the neighborhood at low rpms, there’s only one explanation. That’s right, my guess is an exhaust issue. Loading the motor like this is known to exacerbate a loose or rusty rattle in the exhaust system. And if you live in the rust belt, you can “bet your sweet bippy” that one or more exhaust part is rusted to the point of rattle.

So here’s the advice: find a (non-franchise preferred) exhaust shop in town and ask them to look under your ride. I suspect the rattle is a heat shield on the catalytic convertor, but it could be any welded point on the system. Bad mufflers or resonators are entirely possible. And remember, if you can replace it with an OEM-equivalent part, you can do better in the aftermarket for about the same. But please, no ricer fart pipes, keep the upgrades sane.

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.