JD_AMG

I already did a search and didnt come up with to much. I just want to know a few things here.
The "knocking" sound I get is at WOT between 5000-6000RPMs, and kinds sounds like when your behind a truck and gravel is getting flung at the front of your car. My car is stock other than the muffler in my sig and a 160* thermostat, and just got its oil changed. It has 38,000 miles and im running shell 93 octane ("vpower"). The previous owner (I just got this car like 2 weeks ago) said he ran 87 octane and didnt have any problems(he drove it since it had 20,000 miles), but didnt run it hard.
At any other RPM the car is fine, and its seems to still pull hard even when the knocking sound is happening during 5K-6K RPMs, and Im sure its pretty healthy, I churp 2nd gear easily.
So im wondering if my timing is still retarted from the previous octane (its only been through like 2-3 tanks of premium gas so far) or is something wrong? If I have a bent pushrod(s) wouldnt the engine be acting funny at all the RPMs? Any suggestions would be greatly appreciated.

Adrenaline_Z

That desciption doesn't resemble combustion irregularities like detonation.
How often do you hear this sound? It could be suspension, or driveline
related?

Not likely. The computer would have adjusted by now.

JD_AMG

I only hear it when in at WOT around 5K-6K RPMs, in any gear (well I havent made it past 3rd at WOT yet)
I was thinking if it wasnt engine related, maybe its the tranny mount, or exhaust that is loose or something...

Adrenaline_Z

Would you say what you hear sounds more like pennies shaking in a glass
jar, as opposed to a rock hitting the car?

Also:

Does the sound occur once in sixty seconds...or serveral times per second?

RedZoutlaw

Good question, I have similar noises at high RPM. I was told it could be carboned up since I dont really beat my car too much (more lately). Gonna watch this thread to see what others say.

1QuickT-A

iTrader: (12)

Sounds like the valves could be rattling possibly.. but they should do it under a load at lower rpms as well.. like say going up a hill in 5th or 6th gear and the engine is bogged down.

bowtieman81

iTrader: (35)

Sound to me like your engine is pinging. My buds 01 SS did the same thing, on the dyno it was very obvious. He had some decent pinging at WOT right around 4500-5500 rpm because he was running to lean (about 13.2:1 A/F)

Did the previous owner do anything else to the car? If he changed the tune that might be part of the problem. Has the MAF been descreened (we determined that we damaged the MAF wires on the SS)?

First, I would check your fuel system. Have you changed your filter? If not do it. Then check your fuel pressure. Sounds like the previous owner ran crap gas in it all the time (which means he was an idiot, but off topic). You might have some partially clogged up injectors.

Other possibilities might be an air leak around the intake system.

WS6gunner

Like mentioned above, definitely check that MAF. If it's been descreened and ported it could cause a similiar sound to what you've described.

JD_AMG

Its not really a pinging sound, its more of a knocking sound, like a rattle.

This sound is consistant at WOT near redline, then i switch to 2nd, run that gear out, and near redline it does it again.

But thats interesting that you mention a 'once in 60 seconds sound.' Because at idle I have a rattle that occurs about every 5-10 seconds. It rattles for about 5 seconds, goes away, and then rattles again in another 5-10 seconds later. I was told that its probably just because I have a manual.

JD_AMG

hmm, but they dont. I drove under 1000RPMs in 6th and 5th (just to see how the engine reacts) and I get no rattle, or knocking sound.

JD_AMG

All he said was that he put a 160* thermostat on it, and the flowmaster exhaust. Also he changed the O2 censor because of the muffler swap.

How would I know if the MAF has been 'descreened'? (what is the MAF?)

When the oil was changed the shop also changed the fuel filter.
How do I check my fuel pressure? (yeah, im still learning)

bowtieman81

iTrader: (35)

The MAF is the mass air flow sensor. It is a round sensor between the air intake box and the throttle body. This link should help you figure out where it is
http://www.installuniversity.com/ins...sity/index.htm

To check fuel pressure you need a pressure gauge. I would just buy one unless a shop will do it for free. I think Sears has some for ~40$. There is a test port on the driver's side fuel rail at the front. Its a schraeder valve with a little cap on it. Hope that helps.

bowtieman81

iTrader: (35)

Oh yeah, the MAF screen is a honeycomb screen in front of the sensor wires. It will be obvious if it is there or not.

JD_AMG

Thanks for the help.
Ok so I just got to school (I have 15 minutes before my exam starts).
I gave it 3 good runs on the highway on the way here, switched up a little after 5500RPMs in 1st and 2nd (then had to back off, I was already speeding when I left 1st gear...)
No knocking noise on all 3 runs...
Its about 70 degrees right now, and supposed to get up to 90 today. Ill give it more runs later when I leave here around noon.

Keep any suggesting coming, and ill check the MAF later when I get home.

Camaro ChriSS

You should really get someone with autotap or any other diagnostic tool to read your engine while driving. This will help to narrow things down.

Other than the flowmaster, did he bychance replace the y-pipe at some point, or have headers? I'd have a look as you MAY just have something banging a floorboard, or the crossmember. Its possible.

JD_AMG

He told us no other mods were done to the car.

Im at home now (gotta go back at 2:45) and ran it a few times. Im not getting any knocking now... Its weird. Ill keep you all updated.

Adrenaline_Z

Detonation is a higher frequency sound than the sound you describe.
The knock sensor is designed to pick up frequencies around 5000 Hz which
is out of range for a tone of a rock hitting the front end of the car.

I think we can pretty much rule out detonation 99.9% based on your findings.

Do you have any device to record the knocking sound and post a wave file?

Till

After installing the vararam, I got a new sound at high speed, high rpm and full throttle. It sounded a bit like what you describe, I rather thought of it sounding like "crushing dry leaves in your hands". This only occured at speeds over 140mph, I guess it

The pcm did not record any knocking, although it most likely was. Retarding spark led to a normal, healthy engine sound. (Top speed suffered a bit from retarding the spark, so I clearly didn't find the best tune for that.)

Till

JD_AMG

Well I just took it out again, and nothing. Its not making any noises...
If it comes back ill be sure to come back to this thread, thanks for all the help.

JD_AMG

Interesting.
Well this is definetly a 'gravel hitting the car' noise, the first time I heard it I looked in the rear view mirror expecting to see a gravel patch and dust (I thought maybe I rode over gravel). Then later I noticed it was comming from the front of the car.
Well, like I said its gone now... (or for now...)