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Topic: Just Wondering

in Forum: C4 Engines


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Just Wondering (1/10)
 4/14/13 2:02am
RitaJean
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Mesa, AZ - USA

Vette(s):
1995 Coupe Red, automatic, all original, haven't changed a thing -- except the tires, battery, stuff like that. You know what I mean!


Joined: 4/26/2011
Posts: 64

My Vette makes a pinging/knocking sound when I accelerate hard - especially in the summer with the A/C on.  I had a lot of work done to it and asked the mechanic to replace the oxygen and knock sensors.  They didn't because they said they checked out fine when hooked up to the computer.  (I use good gas, highest octane I can.)

Any comments or suggestions? 



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Re: Just Wondering (2/10)
 4/14/13 3:04am
Big Mike 49
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San Jose, CA - USA

Vette(s):
1988 Corvette / Blue Pearl


Joined: 5/10/2012
Posts: 81


Have your Timing checked Ermm



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Re: Just Wondering (3/10)
 4/14/13 1:55pm
The Car Whisperer
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Andover, MA - USA

Vette(s):
1986 Coupe


Joined: 3/22/2009
Posts: 50

Even with the timing dead on you may get knocking on hard acceleration with todays methanol/gas mixtures that are sold almost universal now.  I have the best luck with Mobil Premium here.  From what I have seen and heard, a light knock is not a major issue, severe knocking can be devastating.  Knock sensors are a separate animal.  They can give incorrect feedback to the electronic timing if they are tightened too much or too little into the block. 

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Re: Just Wondering (4/10)
 4/15/13 9:59pm
codeblue
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Castro Valley, CA - USA

Vette(s):
94 C4 roadster LT1 Automatic triple black. My first Corvette


Joined: 3/1/2012
Posts: 10

Check your EGR system, make sure its not pluged and all the hoses  that controll  it are hooked up and in good shape. Low grade fuel, to much timing, over heating or lean mixture can all cause this problem. Good luck!!
Re: Just Wondering (5/10)
 4/16/13 11:30am
pski88
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Buffalo, NY - USA

Vette(s):
1988 coupe all original 21,000 miles


Joined: 6/25/2010
Posts: 125

silly question but are you running premium in the car? makes a huge difference....in the '88 owners manual it states premium fuel recommended.....not sure if previous owner didn't care, didn't know or whatever but after 2nd tank of sunoco 93...it ran MUCH better and stopped knocking on acceleration....

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Re: Just Wondering (6/10)
 4/16/13 10:39pm
Adams' Apple
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Duncanville, TX - USA

Vette(s):
1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.


Joined: 3/18/2009
Posts: 2230

codeblue said: Check your EGR system, make sure its not pluged and all the hoses  that controll  it are hooked up and in good shape. Low grade fuel, to much timing, over heating or lean mixture can all cause this problem. Good luck!!

+1 on the EGR. And, as already stated, minor knock isn't an issue....these engine can take quite a bit of that, nut excessive, continuous knocking/pinging is damaging, and needs to be corrected. You said you used the best fuel you can get, so that's good. I wonder how they checked the knock sensor? If it is not responding, or not responding quickly enough, it can certainly cause excessive ping.
Over advanced timing can do it, too, as can engine temps that are too high. A vacuum leak can cause a lean mixture, and create a ping.
So many possibilities....



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Re: Just Wondering (7/10)
 4/22/13 2:54pm
RitaJean
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Mesa, AZ - USA

Vette(s):
1995 Coupe Red, automatic, all original, haven't changed a thing -- except the tires, battery, stuff like that. You know what I mean!


Joined: 4/26/2011
Posts: 64

pski88 said: silly question but are you running premium in the car? makes a huge difference....in the '88 owners manual it states premium fuel recommended.....not sure if previous owner didn't care, didn't know or whatever but after 2nd tank of sunoco 93...it ran MUCH better and stopped knocking on acceleration....

Yes, I stated I ran good gas, highest octane I can.


Thanks to all for tha suggestions.  I'll print your comments out and start checking the items you mentioned.



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Re: Just Wondering (8/10)
 4/23/13 11:41am
hwatkins
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Chester, SC - USA

Vette(s):
1993 Convertible Quasar Blue


Joined: 3/20/2009
Posts: 17

RitaJean, is your '95 throwing any codes?
Re: Just Wondering (9/10)
 4/23/13 5:58pm
RitaJean
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Mesa, AZ - USA

Vette(s):
1995 Coupe Red, automatic, all original, haven't changed a thing -- except the tires, battery, stuff like that. You know what I mean!


Joined: 4/26/2011
Posts: 64

hwatkins said: RitaJean, is your '95 throwing any codes?

No.  I'm seeing no codes on the dash info center and none are showing up on my mechanics computer.  All items like the ERG valve, the O2 sensors, knock sensors show they are working okay. 
I've had it "scoped" at my mechanics and according to the computer there is nothing wrong with the car.
Just causally moving down the road, no A/C, under no load, it runs - just okay.  Especially in the early morning (I leave for work at 4 AM).  And in the winter/fall months it isn't as bad.
But when I drive it like a Corvette, especially a hard acceleration - like getting on the freeway - with the a/c on it pings and knocks.  I live in Arizona and the hotter it gets the more noise it will make.
The frustrating thing is my mechanic says he can't find any thing wrong and is of the mindset he won't replace any parts that he can't determine there's a problem with.  So, I'm thinking of tearing into it myself.  I have done some work on it, I'm fairly mechanically inclined, I just need the advise of my C4 registry guys to make sure I'm headed in the right direction.




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Re: Just Wondering (10/10)
 4/24/13 9:10am
tbirdsps
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Ridgecrest, CA - USA

Vette(s):
1990 Coupe


Joined: 2/19/2013
Posts: 117

Well good on your mechanic for not changing parts for nothing.  But, besides checking codes and scoping the engine did he do anything else?
 
Let's assume that everything checks out as he says.  Did he force the EGR open at idle to see if the engine stalls as it should?  If not he or you should.  If the engine does not stall it means the EGR valve or it's passages are blocked with carbon thus disabling the system.  Electronically it can be fine but still be bad.
 
Knocking is the result of only one thing.  The combustion chambers are too hot or even the carbon on the tops of the pistons or valves is causing pre-ignition (knock).
 
If you find that the EGR is blocked by carbon you'll have to remove the valve and clean the carbon out of the passages on the valve and possibly on the intake manifold too.  Time consuming and spendy if you have to pay someone to do it.
 
If it's in fact working properly and the engine stalls when you open the valve then get some of that GM engine top engine cleaner, follow the intructions and it does a great job of removing carbon build up in the combustion chambers.
 
Sever knock, not momentary light pinging, will cause damage.  Broken valves and holes in pistons and/or cracked heads.


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