Getting High RPM Knock.
Thread Starter
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Getting High RPM Knock.
....ok help me out. Smallblock pointed out that my car was getting severely pronounced Knock at high RPM at our autocross last Saturday. So.... what should I do. We could hook up the diacom and get some data, but I'd like to try some self diagnosis first. Here is some info....
a) 94 Sunoco fuel all the time
b) New Plugs
c) New MSD 8.5mm Wires
d) Stock Distributor/Cap/Rotor/Coil (as far as I know)
e) Initial Timing at 6 degrees
f) Hypertech Stage II EPROM
...it is happening over 3500 RPM, and the tach is also fluctuating pretty good at the same time while it's occurring. Where should I start?
He suggested removing the Hypertech, putting my stock EPROM back in, and just upping the timing a bit on my own since the Hypertech basically only ups the timing curve in the lower RPM and turns the fans on sooner. I already have a fan override switch, so i can turn them on at will.
All ideas welcome, thanks.
a) 94 Sunoco fuel all the time
b) New Plugs
c) New MSD 8.5mm Wires
d) Stock Distributor/Cap/Rotor/Coil (as far as I know)
e) Initial Timing at 6 degrees
f) Hypertech Stage II EPROM
...it is happening over 3500 RPM, and the tach is also fluctuating pretty good at the same time while it's occurring. Where should I start?
He suggested removing the Hypertech, putting my stock EPROM back in, and just upping the timing a bit on my own since the Hypertech basically only ups the timing curve in the lower RPM and turns the fans on sooner. I already have a fan override switch, so i can turn them on at will.All ideas welcome, thanks.
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Re: Getting High RPM Knock. (scorp508)
First thing : X the hypertech. Then test.
Thread Starter
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From: Boston, MA
Re: Getting High RPM Knock. (Vic'89)
Can you hear the knock ? Or are you using sofware to view the knock ?
Thread Starter
Team Owner
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From: Boston, MA
Re: Getting High RPM Knock. (Vic'89)
Any chance you could run 100 octane unleaded gas in the car to narrow down the problem area ?
Maybe if I time it right, the next time I go to the strip I can get 1/2 tank or something.
Thread Starter
Team Owner
Joined: Mar 2000
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From: Boston, MA
Re: Getting High RPM Knock. (Vic'89)
Just let your tank run close to empty and then add about 4 gallons of 100. Then do your WOT testing and listen for knock.
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Safety Car
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From: Long Island, NY
Re: Getting High RPM Knock. (scorp508)
If you have knock with 100 octane, then you have some ignition issues or alot of carbon buildup on the pistons.
Make sure none of your wires are arcing. How's the fuel pressure at WOT ?
Vic
Make sure none of your wires are arcing. How's the fuel pressure at WOT ?
Vic
Burning Brakes
Joined: Dec 2000
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From: Lafayette LA
Re: Getting High RPM Knock. (scorp508)
You don't need a whole tank full of 100 to stop the knock. Usually 95 octane will do it unless you have very high compression or serious problems. You can probably test it with 2 gallons of the expensive stuff. See calculations below.
I'm not suggesting that you do this all of the time - just to see if you get rid of all of the knock. Make sure it's unleaded.
You really need a scanner to track the problem down. I suspect you have good plugs and wiring and no carbon deposits. I don't remember your compression ratio, but that may be part of it.
Some other common causes:
Bad Gas - it happens.
Running Lean - vacuum leaks, fuel pressure, bad injector (s).
High Temperature - IAT as well as H20.
Maybe a little bit of all of the above. Finding the problem can be tough.
I would agree with ditching the programming until the problem is resolved.
Here is the formula to figure out your octane when blending:
Gallons of old gas X octane = product 1
Gallons of new gas X octane = product 2
Sum of products / sum of gallons = blended octane.
Example with 10 gallons of 92 blended with 2 gallons of 110:
10 X 92 = 920
2 X 110 = 220
1140/12 = 95
Good luck, it's driving me crazy.
I'm not suggesting that you do this all of the time - just to see if you get rid of all of the knock. Make sure it's unleaded.
You really need a scanner to track the problem down. I suspect you have good plugs and wiring and no carbon deposits. I don't remember your compression ratio, but that may be part of it.
Some other common causes:
Bad Gas - it happens.
Running Lean - vacuum leaks, fuel pressure, bad injector (s).
High Temperature - IAT as well as H20.
Maybe a little bit of all of the above. Finding the problem can be tough.
I would agree with ditching the programming until the problem is resolved.
Here is the formula to figure out your octane when blending:
Gallons of old gas X octane = product 1
Gallons of new gas X octane = product 2
Sum of products / sum of gallons = blended octane.
Example with 10 gallons of 92 blended with 2 gallons of 110:
10 X 92 = 920
2 X 110 = 220
1140/12 = 95
Good luck, it's driving me crazy.
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Re: Getting High RPM Knock. (scorp508)
My bet's on the Hypertech chip..... I've seen the timing tables in these things! It did the same thing to my '85 when I had a Hypertech in there.
Thread Starter
Team Owner
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From: Boston, MA
Re: Getting High RPM Knock. (Sarkee)
If the dampner is good, the midpoint will fall right on the timing notch in the dampner."
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From: SE NY
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Re: Getting High RPM Knock. (scorp508)
Scorp, upgrading my ECS module (see my site) eliminated my "false" knock count during a WOT run problem but yours sounds a little different.
You need some scanner data to find out what's up inside.
Does it happen only at WOT or only above 3,500 RPM?
If you back base timing off say 5-6 deg does it change (decrease)?
Is everything tight inside the dist cap?
You need some scanner data to find out what's up inside.
Does it happen only at WOT or only above 3,500 RPM?
If you back base timing off say 5-6 deg does it change (decrease)?
Is everything tight inside the dist cap?
Thread Starter
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Re: Getting High RPM Knock. (65Z01)
You need some scanner data to find out what's up inside.
Does it happen only at WOT or only above 3,500 RPM?
If you back base timing off say 5-6 deg does it change (decrease)?
Is everything tight inside the dist cap?
Does it happen only at WOT or only above 3,500 RPM?
If you back base timing off say 5-6 deg does it change (decrease)?
Is everything tight inside the dist cap?
Drifting
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From: Holliston MA
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Re: Getting High RPM Knock. (scorp508)
Scorp - put in a set of fresh plugs. Take the car out for a beating then lets look at the plugs to see if the noise is actual knock. The plugs should show detonation as well as timing issues.
Team Owner
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From: SE NY
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Re: Getting High RPM Knock. (Sarkee)
Assuming you have no codes, find no problems within the dist and damper alignment is fine (it hasn't spun slightly) I would suspect the Electronic Spark Timing (EST) module or the Electronic Spark Control (ECS) module.
