unusual noise when accelerating under load.

That sounds like pinking/pinging/detonation which happens when the ignition is advanced too far - but the Commodore has knock sensors which in theory detect this problem and react by retarding the ignition.
Have to think about that one!

 

Do non HSV enhanced cars still have the knock sensors? I didnt think they did.. (Im not saying you're wrong, im just asking a question)

 

yeah they did part of the engine management system.

is it simply caused by higher rpm's (revving in neutral staying still does it??) or only on gear kickdowns when driving?

 

Ive got similar problem with my missus car. Vr Auto. When its in top gear, put foot down to make it kick back a gear, when your foot is about say 50% the way before it shifts back a gear, it makes this noise that sort of sounds like when you drive on the edge of the road lines on the highway that have the bumps which cause vibrations to wake you up if you veer off the road. But then stomp it the whole way, it shift back a gear and then is right.... Is this noise similar to yours at all?

 

Id be getting it put on a dyno.See if they can reproduce it that way and then try to find out whats going on.

 

Maybe the knock sensors are not working (or one of them).......you can test them by hitting the block with a hammer and revs should alter as it still sounds like pre-ignition/pinking to me. Maybe a codes test will reveal something as I think bad knock sensors leave a code. The gregory manual details how/where to hit with hammer.
http://forums.justcommodores.com.au...22307-checking-error-codes-vr-vs-revised.html

 

I have the exact same problem, described the same as dawg's...got no idea what it is, but i'd love to find a solution because it really doesn't sound too good! I'll give the knock sensors a go tommoz, but i've had no codes logged.
Cheers

 

It is interesting that u say that, cos i did notice the sound had went away for a couple of weeks after i did a long distance trip travelling at 110km/h most of the way, and im pretty sure I used Shell V-power in the tank for that long run...and it must have cleaned out something, cos for a week or so after that, the noise didnt happen.
I haven't had a chance to check the knock sensors, but I did check the codes, and there was no codes logged.
I'll try putting in a bottle of injector cleaner cleaner which will up the RON and see if that fixes it!
Cheers

 

Do the "hitting the engine block with a hammer"test Hako mentions in his post,it will tell you if the knock sensors are working.I will only use 98 octane fuel(shell v-power,caltex vortex 98 or bp ultimate.)and it runs so much better on it,I wont use anything else.The engine should not be pinging anyway,even on 91 octane fuel.The knock sensors,once they detect knock/pinging, tell the ECU to retard the ignition timing to compensate for the lower octane fuel.

 

There is a test where you tap the engine whilst idling and the revs will change - have seen it on this forum a number of times so someone will nkow it. I've copied the stuff from Gregorys but it presumes you have a code....however code 93 appears to come on if the knocking is for more than 10 seconds. Hope this helps.

Gregorys says:
Code 43, 93 Knock sensors.
With the ign off, measure the voltage at the ECU terminal C12 while an assistant taps the alternator bracket with a hammer.
If the voltage is above 50 AC millivolts, check the wiring and connections between the ECU and the knock sensors. If no fault can be found and the fault code continues renew the ECU.
If the voltage is below 50 AC millicolts, check the wiring for continuity and shorts between the ECU and the knock sensors.
If the wiring is not faulty, disconnect the wiring and measure the resistance to earth at each sensor. Renew the faulty sensor(s).
Code 93
This code is set if the ECU receives a knock signal for more than 10 seconds. Check the engine for audible knocking or excessive mechanical noise. Renew the ECU only if the engine is not at fault.

 

I had this noise like 4 or so years ago, i would be driving on the highway in overdrive then hit a hill and it wouldnt kick down and would make that noise of driving over the 'audible lines' but if i took my foot off the acclerator then back on it would kick down and be fine. drove with it like that for a year then my car one day started to bunny hop (yea bunny hopping an auto is not good ) so i took it to an auto mechanics and they told me the clutch plates were 60% all gone and 40% nearly there due to a crack in the torque converter and throwing metal all through the auto. So i suggest anyone who has this problem get it seen to as soon as you notice it happening or you will be up for some $$$ if you leave it go and need a full reco (or manual conversion like i did at the time)

Hope this helps ya's

 

Hey all,

I have a similar problem. Not sure if you've lowered your car Tony but when I have mine loaded up, can happen with as little as 2 ppl in the car I get that similar kind of sound like crunching gears on a bicycle like you said in the OP.

My noise comes from the back of the car and is actually the join in the drive shaft just before the diff rubbing on the body pan. The bolt heads and small bumps on the join make this sound.

To fix it i'm going to try to replace a small rubber that sits on the body pan immediatley above the front of the diff and i'm assuming is meant to stop this. I guess being 16years old is probably perished or shrunk a little bit.

Hope this helps

Jack

 

Hey Jack,

How did you go replacing the rubber bit? Did it fix the problem?

 

Hey mate yea its a small diff rubber that sits on the body pan above the front of the diff. Also my bump stops were shot so I replaced them too and it fixed it up, however just a month or so later I was under there and they completely shot again so I think i'm up for some heavy duty ones.

Jack

 

This is exactly what mine has been doing on and off for 18 months, I don't accelarate quickly to "drive around" the problem, is quite a worrying sound I would really like to know what it is, did you get to the bottom of your problem ??