By on November 15, 2010

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.

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37 Comments on “Piston Slap: The Kid’s Got a Point, Dear...”


  • avatar
    Stingray

    Sadly those wheels didn’t make it down here, because those cars look awesome with them.

  • avatar
    ash78

    I’m thinking exhaust heat shield or shattered catalyst. I’ve seen both, and they’ve had very similar symptoms.
     
    If it’s the cat, you can gut it to get rid of the rattling, but it’ll probably throw a CEL if it hasn’t already. High-flow are available for cheap, but opinions are mixed on whether they do much in a modern engine.
     
    Don’t shift into first while moving. Yeah, it’s a blanket statement, but it’s true 99.9% of the time you’re not autocrossing.

    • 0 avatar
      protomech

      Even in autocrossing, I usually stay in 2nd gear most of the time once I leave the start gate. Unless it’s a super-tight turn (5-10 mph), changing down to first seems to waste more time with shifting (and possibly breaking traction) than you gain with more torque.

  • avatar
    jimbowski

    Ultimate win:  have the independent shop stick on an exhaust cutout somewhere after the collector (electrically controlled if you got the cash).  Keep closed for neighborhood and family driving.  Open her up for loud and bodacious hooning.

  • avatar
    Variant

    Yup, I’m thinking shattered cat too.  Get underneath and bang on it and you’ll know for sure in short order.

    • 0 avatar
      celebrity208

      …after it’s cooled down.

    • 0 avatar
      Silent Ricochet

      Just did that. Didn’t know what I was looking for, but I didn’t hear anything abnormal. The cat and the exhaust line shook ever so slightly when I banged on it with my fist. Maybe that’s my problem?

    • 0 avatar
      ash78

      @Silent Ricochet
       
      Some movement is normal if you think about it–the exhaust is tied to the engine, and the engine has to move slightly on its mounts. This keeps it from rattling you (and the chassis) into submission. But sometimes failed engine mounts can lead to excess play, which in turn can cause the exhaust to rattle against the heat shielding underneath (as myself and others have suggested). So the movement is probably normal.

    • 0 avatar
      garythompson

      You might check engine and transmission and exhaust mounts while you are at it. [oops! just noticed ash78\'s comment above. I have had bad mounts cause problems like this.]
       

  • avatar
    geozinger

    Dead catalytic converter, possibly one or more hangers broken, or just a broken exhaust pipe. Diagnosing these things without seeing the car is like trying to phone in brain surgery.
     
    I replaced the cat on my Sunfire GT with a Magnaflow, turns out it was a good deal. Great sound, and my exhaust smells like unicorn farts (kidding). No really, if it’s the cat, I would recommend the Magnaflow. YMMV.

  • avatar
    racebeer

    My bet is heat shield around the cat.  I had the same thing happen on both my ’98 Firebird and my daughters ’98 Sunfire with the same 2.4L motor.  However, one other place to look — the downpipe coming out of the exhaust manifold on the back side of the engine.  I had a leak in the flexible connection there on my son’s 99 Grand Am with the 2.4L motor, and it sounded just like a loose heat shield.  It really fooled me for a while!!

    • 0 avatar
      Ian Anderson

      I’ll also throw money at this. The old 4.3V6 S10 I drive rattles annoyingly when in park at an idle, or when driving at at near idle speeds (~15MPH through a school zone). Put it in Drive one day in the driveway and had a neighbor hold the brake while I crawled alongside with a leather glove on. Turned out to be the heat shield on the cat. Fooled my father and I for sure, we thought everything from U-joints to knocking/pinging.

  • avatar
    Autojunkie


    Sounds more like a wheel bearing (front) going bad.

    • 0 avatar
      william442

      That, or a cv joint. Great opportunity for a new exhaust system at worst.

    • 0 avatar

      CVs and bearings aren’t (usually?) RPM dependent, just speed dependent.

    • 0 avatar
      Autojunkie

      Sajeev. You are right, but the fact that it makes noises under varying conditions of drivetrain torque (turning, weight distribution, etc.) can also cause the front wheel bearings to make a slight griding noise (in the early stages of wear).

      Of course, the it’s difficult to describe a noise in words so I may be on the wrong track myself, but the description sounds very familiar to me. If it is a front wheel bearing, it will get noisier in time and not only appear under certain conditions.

    • 0 avatar

      Good point.  I think all of our replies covered the bases, reaching the limits of armchair quarterbacking.

    • 0 avatar
      Silent Ricochet

      Sajeev. I’d like to thank you again for all your help and publishing this article. I went out for a few errands today and brought a video camera with me. I recorded the noise several times, and the noise is audible in the videos I’ve. But nothing compares to the in-person experience.
      Just to clarify, the noise happens whether I’m turning or going straight, and only happens when the RPMs are below 2000 and I hit the gas. I’m thinking you’re right about either a heatshield or an exhaust issue. It seems to be a much more viable issue than a wheel bearing or joint.

    • 0 avatar

      99% sure it’s the heat shield, but if it’s anything else…well, you know the right thing to do.

  • avatar
    Educator(of teachers)Dan

    Performance cat and Flowmaster FTW!  Or performance cat, Y-pipe, dual performance mufflers FTW!  Won’t be a fart can, should sound wicked.  Make the old hot rodders in the neighborhood think the kid might be alright after all.

  • avatar
    V572625694

    Are we sure this isn’t just knocking from lugging the engine?

    • 0 avatar
      Silent Ricochet

      Positive, lugging the engine produces a different noise. Heard it plenty when learning to drive stick shift in this car.

    • 0 avatar
      cdotson

      +1
       
      High throttle at low rpms sounded like knock to me.  I learned to drive in a 1984 Plymouth Voyager with the 2.6L Mitsubishi engine and I distinctly remember the “marble in a coffee can” sound that reflected off every passing Jersey barrier.

  • avatar
    mistrernee

    I had a Camaro that made what I assume to be the same noise you have.
     
    Several trips to the dealer with various parts getting replaced never fixed the issue and I gave up on the car after several expensive services (that included a new clutch that went bad within a week of being replaced). If it was just the exhaust making the noise it isn’t surprising but rather irritating the service departments never picked up on it.
     
    The 1-4 skip shift made the sound almost unavoidable.

    • 0 avatar

      There’s more labor on a clutch job…plus most (all?) dealers don’t do exhaust work, that gets farmed out elsewhere.

    • 0 avatar
      mistrernee

      Oh, the clutch was a separate issue and unrelated to the rattling noise. It was just the one that made me throw in the towel and get rid of the car.

      Oh.. That and every time I turned the engine over I swear I could hear the LT1 saying “Today, I kill you…”

  • avatar
    Sinistermisterman

    I’m no racing driver, but having taken part in several road rallies in 2 litre fwd cars in the UK I must ask this question. How or why do you shift into 1st gear going around a corner? The only time I ever used first is to pull away from a stop or when handbraking it around the very tightest of hairpin corners on single track country roads… As I was learning to drive fast I found that trying to ram it into first gear at any speed above 5-10mph is just pure torture for the poor old transmission and slows you down far more than you need to.

  • avatar
    kksulli

    Sounds like the downpipe flange. I had that happen on my ’98 Z24 when I had it. Over time the flange connection weakens from engine movement and the gasket burns out.. when it heats up the parts separate and make a buzzing/raspy sound.. at least I think that was what happened :) its been 10 years.

  • avatar
    zerofoo

    Back in my High-School/College days I had a 1987 Cavalier Z24 – Red, Eibach springs, Tokico dampers, recaro leather buckets, and a high-flow cat and a flowmaster muffler.  That 2.8 never sounded better.
     
    The digital dash was crap (as was the rest of the interior), but that 2.8 took a beating, and just kept going.
     
    -ted

  • avatar
    BMWfan

    You may have a broken clutch disk spring, or a loose or broken clutch hub spring.

  • avatar
    nrd515

    I had an ’86 IROC Camaro that after it was about 3 months old started making this really odd “DONK” noise when getting on and sometimes off the throttle. The dealer looked at it, drove it, looked at it, drove it again, and basically told be to live with it. I went over to one of the few, even then, old gas stations and had this old guy I’ve known forever look at it, and he he found it right away. When the dealer had replaced the right strut they had either pushed the exhaust to clear something, or the lift had hit it. the hanger was almost all the way out of the rubber mounts in the back. He took the car off the lift, got down on the ground, and took his foot and pushed the hanger back into the mount. That was it. I went to the dealer a couple weeks later for an oil change and to have a trim piece replaced that was warped, and told the service manager what it was. He looked like he was going to kill himself. I showed him what the old guy did, and he said, “I can’t believe we all missed it!”. I kind of lost my faith in the dealer techs at that point.
    Same thing happened when my 93 Grand Cherokee developed a scary shake when braking at anything over 40 or so. More than one dealer looked at it, Procare looked at it, and said the front end was fine, but that my AC was leaking and wanted some insane amount to fix it (It was leaking, but it was a freebie every time the condenser cracked, about every 16-18 months). They all had the shake when driving it, but found nothing that would cause it. I asked about the steering stabilizer over and over again, and they all said it was fine. It was getting worse, to the point where I was almost changing lanes if I slammed on the brakes. Finally, I couldn’t take it anymore and had them change out the steering stabilizer. I went down the freeway at 65, and slammed on the brakes. No more shake. I drove it back to the dealer and told the service manager, “It’s gone!”. He went and dug the old stabilizer out of the trash and they looked at it and swore up and down there was nothing wrong with it. When I went back 3 months later for service, he comes up and told me that they had about 4 or 5 more people come in with the same shake, and the stabilizer fixed it in all of them. I got a free oil change for being the pioneer who solved his own problem. These GC’s all had about 60K or so on them. The service manager told me that all of the other stabilizers were “ok” too.

  • avatar
    Beerboy12

    I would look at what is causing the vibration. Below 2K revs on a big four like that is always going to cause quite a bit of vibration but it would appear as if there might be more than normal. Its possible you are looking at some internal wear, rings or big end bearings and the like at that mileage, especially if the motor has had its share of hooning. Check if it has a chain or a belt for the cams. If its a chain it may need adjusting.
    If all that is fine then you have something loose. If not the exhaust (check all rubber mounting) then I would test the shocks, steering and suspension. There are a billion little rubber bushes in those areas that could have perished.

  • avatar
    George B

    Had a similar issue in the past due to a worn out engine mount.  An accessory pulley could shift just enough to rub against something and make a sound when the engine was under load.

  • avatar
    JimC

    I think everybody pretty much whipped the noise issue.
     
    For the 2-1 downshift, yeah, don’t bother shifting into 1st unless you’re almost stopped.  Even as late as the 1950s and 1960s there were still manual transmissions built with non-synchro first gear.  Food for thought.  But…
     
    Why is your 2-1 so difficult?  At 128,000 miles it is worth your while to change your transaxle oil- just make sure you do it right (get the right oil, remove the filler plug before you remove the drain… just in case the filler won’t budge, be careful not to underfill on the refill).  That and some parts of the clutch might be wearing out- is there a freeplay adjustment on these cars?  (Not all manual transmission cars have that though.)

  • avatar
    MRL325i

    Slightly OT, I looked at one of these today as a first car for my son.  It was a 2000 Z24 with an autobox.  The guy kept it in very good shape, and it had less than 60k on it.  But, man, what a POS.  The I could feel the frame under the seat cushion, the doors needed a good slam to latch — just everything about it seemed bean counted to death.  Maybe it is a decent car, but I couldn’t get past the overall crappiness of the thing.


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