O/T- What causes an engine to clatter

[Nancy Howell]

My 96 Chevy has a 5.7L Vortec. It just doesn't like regular gas. It clatters (I believe pre-ignition is the technical term) slightly under light driving and sounds like I've got a bunch of tin cans rattling around under the hood if its under a load. With mid-grade, it doesn't clatter much under light driving, but still quite a bit under a load. With premium, no clatter at light driving, and slight clattering under loads. What gives? I have a friend with a 95 that runs fine on regular.

 

[Anonymous-0]

Sounds like you might have a faulty knock sensor.The sensor should detect pinging and retard the timing to correct the problem.

 

[Anonymous-0]

Maybe carboned up, maybe needing timed. Fill her with premium and go test Highway patrol radar. Have you changed "brands" some times one midgrade is someone elses premium, really should be 89 octane is 89 octane but it ain't.

 

[Allan in NE]

Better be fer gettin' that fixed.

Not pretty when they start foggin' oil out the back from those burnt pistons.

Allan

 

[sd pete]

That could be it. I have a 97 2500 5.7 and it runs good on regular gas. But it sure likes a lot of it. Guess kind of like me and San Miquel beer in my younger days.

 

[old]

In the older engines that was caused by the timing being off a tad bit. I would have the timing checked to make sure its not advanced to much. Also you might try some injector cleaner in the tank which will help if you have a carbon problem
Hobby farm

 

[bradk]

Ignition timing not adjustable on the '96-up Vortechs.Is the SES light on? Knock sensor should pick up on the ping and have the PCM(computer)retard timing.Knock sensor may be faulty.

If all is ok there,you'll have to take to dealer and have them reflash the PCM with the latest & greatest software.

 

[Texasmark]

Had a '97 in a Tahoe. Never heard it knock regardless of driving conditions at 800' altitude and 87 octane.

Drop by your chevy dealer and they may give you a computer test for free. You can drive into the service bay (where they take you in) and ask the attendant to give you an idea what is wrong. Will just take him a second to hook in and read the codes. No charge....for me anyway. Course you may or may not choose to have them fix it and he doesn't know what you are going to do.

Mark

 

[Anonymous-0]

My 2000 vortec sounds like a diesel when you first start it up. As soon as the pistons swell up the noise stops. G.M. said it is piston slap, and its normal. Sounds terrible.

 

[rustyfarmall]

Piston slap is not normal. I personally know one guy that got a brand new engine from GM because of that issue. The new engine did not have the slap.

 

[Walt Davies]

Clutter. Giggle.
Walt

 

[El Toro]

You may have a bad EGR valve. Hal

 

[Allan in NE]

Yep,

The old "Wool over the eyes" campaign. They gave me that song and dance also on a Yukon.

We now drive a Navigator. :>)

Allan

 

[Nancy Howell]

What makes you think my truck has clutter? Its a LADIES'S truck! (giggle)

 

[Nancy Howell]

About a month ago, my mechanic ran some carbon cleaner through the intake. It ran fine on reg. for about 2 tanks, then started the clattering again. Actually think its worse now. It sure didn't like Shell midgrade. Really clattered under a load after filling with it.

 

[oldnnew]

How many miles on it? Could be excessive carbon deposits, bad EGR, clogged fuel filter.....My suggestion is to give it a COMPLETE tune up first, (plugs, wires, cap, rotor, PCV valve, fuel filter, air filter, etc. Try running it after you do this. Let us know how it works out.

 

[KEB1]

That engine should run just fine on cheap gas. Knock sensor should be telling the computer to dynamically retard the timing to keep it from knocking. Take it to someone with a good diagnostic tool & see what"s up...not all error codes will set the SES light. A good scan tool should also be able to monitor timing in real time as your drive to see if its tracking as it should.

Knock sensor on the edge of failure is the most likely culprit, but not the only possibility. Need to know what"s going on before spending a bunch of money throwing new parts at it.

If a knock sensor is cheap and you can replace it yourself, might be worthwhile just to eliminate one possibility. Otherwise, if its not setting the SES light, this is a job for a scan tool that can read the manufacturer unique codes.

Keith

 

[buickanddeere]

If there is that much detonation occuring. There is engine damage happening. Run it on premium until you get it diagnosed and repaired.If it hasn"t happened already. There is going to be broken piston rings or broken piston ring lands.
I agree it sounds like a plugged EGR but the OBDII should have thrown a check engine code with a no flow EGR.
As previously stated the knock sensor has also either failed or the wire/connector is disconnected. Even with a plugged EGR. The ECM should be receiving a knock signal and retarding the timing until the engine is a gutless no knock pig.
If the wrong plugs have been installed. The engine can almost get knocking along like a glowplug model airplane engine.

 

[ncdiesel48]

Agreed same thing with my dads 2000, GM actually had a service bulltin about it. It doesn't hurt a thing these engines are prone to it. His truck now has over two hundred thousand with 0 problems.

 

[Brian Jasper co. Ia]

Being a drivability tech at a Chevy dealer, I would be looking for any DTC's, state of engine tune, thermostat temp, probably want to clean the injectors. I can tell you as a professional, the pour in the tank stuff does NOT do the job by itself. If your spark knock is being caused by carbon build up, it may take more than 1 cleaning to get rid of it. The "through the fuel rail" cleaners burn much hotter than gasoline to burn off the carbon.
Fogging oil into the intake may soften and remove carbon, but it will destroy the catalytic converter and oxygen sensors.
If the thermostat is not keeping the coolant warm enough, that will contribute to deposit formation. What kind of driving do you do? Lots of short in town trips, or highway? Like someone said, get it serviced then go give the local cops radar a workout.

 

[Stockdale Dave]

My 97 Tahoe 5.7 sounds like it's coming apart on acceleration. Always has. 189K and no problems.

 

[bradk]

Is this the same "mechanic" that told you to install a manual front differential cable on your '96 truck instead of fixing the RIGHT way?

I think you need a different mechanic.