False Knocks...where to look?
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,477
Likes: 80
From: Hawaii
False Knocks...where to look?
I have been data loging my runs at the track, and keep on getting a false knock between 4900 to 5100 rpm in all gears at WOT. With the false knock as you know, I am having my timing pulled out in the upper RPM ranges.
I am pretty sure it is false knock, because I have been using 100 octane racing gas, on stock compression.
I have a 93 LT1 with a A4. Installed LT4 heads, 1.6 roller rockers, Hot cam, Shorty headers, electric water pump, Dana44 w/ 3.45 gears.
Any ideas to where to look for the cause of the false knocks?
I am pretty sure it is false knock, because I have been using 100 octane racing gas, on stock compression.
I have a 93 LT1 with a A4. Installed LT4 heads, 1.6 roller rockers, Hot cam, Shorty headers, electric water pump, Dana44 w/ 3.45 gears.
Any ideas to where to look for the cause of the false knocks?
Pro
Joined: Nov 2005
Posts: 658
Likes: 12
From: Clearwater Fl
Im not 100% sure on Vettes as this is my first.
But on normal cars,,, running 100 octance will throw things off. The car actually looks for a knock so the computer knows where to adjust the timing to.
I would try 93 and see if it still does it, or wait for a more informed person to respond.
But on normal cars,,, running 100 octance will throw things off. The car actually looks for a knock so the computer knows where to adjust the timing to.
I would try 93 and see if it still does it, or wait for a more informed person to respond.
Race Director
Joined: Jan 2005
Posts: 10,641
Likes: 13
From: Slidell Louisiana
Originally Posted by James93LT1
I have been data loging my runs at the track, and keep on getting a false knock between 4900 to 5100 rpm in all gears at WOT. With the false knock as you know, I am having my timing pulled out in the upper RPM ranges.
I am pretty sure it is false knock, because I have been using 100 octane racing gas, on stock compression.
I have a 93 LT1 with a A4. Installed LT4 heads, 1.6 roller rockers, Hot cam, Shorty headers, electric water pump, Dana44 w/ 3.45 gears.
Any ideas to where to look for the cause of the false knocks?
I am pretty sure it is false knock, because I have been using 100 octane racing gas, on stock compression.
I have a 93 LT1 with a A4. Installed LT4 heads, 1.6 roller rockers, Hot cam, Shorty headers, electric water pump, Dana44 w/ 3.45 gears.
Any ideas to where to look for the cause of the false knocks?
How about the roller rockers! The LT4 had a different knock module due to the noise of the roller rockers.
Mike
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,477
Likes: 80
From: Hawaii
Originally Posted by bobmic93
James, just curious to what kind of times are you getting with your set up?
Last edited by James93LT1; Dec 18, 2005 at 04:18 PM.
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,477
Likes: 80
From: Hawaii
Originally Posted by STL94LT1
Have you removed the knock sensors? Maybe they were reinstalled too tight.
Also, there should be no need to run 100 octane fuel with stock compression.
Also, there should be no need to run 100 octane fuel with stock compression.
I was running 100 octane fuel to make sure it was not a real knock. Initally ran 92 octane with octane booster, and had the same results.
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Former Vendor
Joined: Jun 2001
Posts: 7,204
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From: St Marys PA
Chances are your right it is false knock. One very common source of knock is your torque converter, which is why good race ones are 7-8 hundred dollars. They handle the power much more effectively than the stock or cheaper style converters.
What I would do and I know MANY go this route is to just zero out the knock retard tables. What this will do is not allow the car to pull any timing, but you can still track if more should occure out of the "norm" false knock, ie if your fuel pump or something should start going bad down the road. Your circumventing the knock sensor's ability to pull timing, but in reality the sensor is not needed if you have a clue what your doing. Nearly every guy I know that runs their car at the strip has theirs unhooked because there just seems to always be something that will trigger it off, and screw up a run. Last thing you need it to do is pull a degree or two for no reason and throw you off a .05sec from your dial-in.
Zero out the tables and let-er eat.
What I would do and I know MANY go this route is to just zero out the knock retard tables. What this will do is not allow the car to pull any timing, but you can still track if more should occure out of the "norm" false knock, ie if your fuel pump or something should start going bad down the road. Your circumventing the knock sensor's ability to pull timing, but in reality the sensor is not needed if you have a clue what your doing. Nearly every guy I know that runs their car at the strip has theirs unhooked because there just seems to always be something that will trigger it off, and screw up a run. Last thing you need it to do is pull a degree or two for no reason and throw you off a .05sec from your dial-in.
Zero out the tables and let-er eat.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Unless you've got some excessive piston slap at that RPM range I would suspect that you've sufficiently changed the internal noise signature of the engine with your modifications. The knock control hardware is calibrated to use the normal expected internal noise as a baseline, and any short term additional (and appreciable) noise in the 5kHz to 6kHz range is interpreted as spark knock. As mentioned, you could just zero out the spark retard ability to get rid of your problem, but that gets risky if you're oversparked in some of the other RPM ranges.
ps: An occasional, but rare cause of false knock is an intermittent connection at the harness/sensor interface. This can corrupt the signal sent to the knock module. This interface is reported to be designed for a limited amount of connect/disconnects. Unplugging the sensor any more than necessary just increases the wear on this interface. (However, if your problem is at a repeatable RPM point I would look for other causes than the connection interface.)
ps: An occasional, but rare cause of false knock is an intermittent connection at the harness/sensor interface. This can corrupt the signal sent to the knock module. This interface is reported to be designed for a limited amount of connect/disconnects. Unplugging the sensor any more than necessary just increases the wear on this interface. (However, if your problem is at a repeatable RPM point I would look for other causes than the connection interface.)
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,477
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From: Hawaii
Thanks Guys, I may just have to zero out my spark retards in that certain RPM range, and do a data run to see if there is any change in the knock counts.
I'm pretty sure that its just the certain combination of my mods, or an item that that I have in my car, that is causing the false knocks. The car runs great in all areas, except when the knock sensors goes off.
I'm pretty sure that its just the certain combination of my mods, or an item that that I have in my car, that is causing the false knocks. The car runs great in all areas, except when the knock sensors goes off.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
If you are able to to zero out your spark retards tables you are also able to see if your fuel pump is delivering all the fuel required. Before to level at zero the spark retard tables , please take a look at the O2 sensor volts values. If at 4500 an up you can see a decrease in O2 volts value (under 850 and worse with the increase of the rpm), your pump is gone and the trick to lower the retard added by the chip can blown your engine.
-Beppe-
-Beppe-
Le Mans Master
Joined: Dec 2004
Posts: 5,789
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From: Myrtle Beach SC
St. Jude Donor '05-'06
Originally Posted by conv90
If you are able to to zero out your spark retards tables you are also able to see if your fuel pump is delivering all the fuel required. Before to level at zero the spark retard tables , please take a look at the O2 sensor volts values. If at 4500 an up you can see a decrease in O2 volts value (under 850 and worse with the increase of the rpm), your pump is gone and the trick to lower the retard added by the chip can blown your engine.
-Beppe-
-Beppe-
Good advice.Yes your problem may be with the noise your mods make but I would want to be sure your knocks are not because it is going lean and making sure everything is correct before changing the software.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by conv90
Before to level at zero the spark retard tables , please take a look at the O2 sensor volts values.
-Beppe-
-Beppe-
False knock can come from a variety of places. As a test, I revved my engine, in neutral (no load), with 0° base timing, on 91 octane gasoline, with my stock 9:1 compression ratio and I STILL got knock counts. If THAT isn't false knock, I don't know what is. On MY car, I can get away with disconnecting the knock sensor, which is what I did.
Any vibration in or near the engine can cause a false knock. I have heard of those that had to reverse a motor mount bolt, so it wouldn't hit on the headers, to stop false knock. Isolating the cause could become a major project.
RACE ON!!!
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,477
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From: Hawaii
Thanks Beppe, and Redeasysport,
Thats a good point, and a good thing to watch out for. I guess I need to install a fuel pressure gage before I remove the timing.
Thanks CFI,
That a neat idea, I did not think of. I need to see if I still get the knock counts at the certain RPM.
Not sure if it can be done, but I was planning to get me the Tunercat program, and see if I can remove the timing retard only at the RPMs ranges that currently gives me the false knocks. This way if there is a real knock, hopefully the knock sensors will kick off and retard the timing at the RPM range above my false knocks zone.
Thats a good point, and a good thing to watch out for. I guess I need to install a fuel pressure gage before I remove the timing.
Thanks CFI,
That a neat idea, I did not think of. I need to see if I still get the knock counts at the certain RPM.
Not sure if it can be done, but I was planning to get me the Tunercat program, and see if I can remove the timing retard only at the RPMs ranges that currently gives me the false knocks. This way if there is a real knock, hopefully the knock sensors will kick off and retard the timing at the RPM range above my false knocks zone.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
On a 90 speed density $8D cal, you can.
Knock retard in Power Enrichment table is rpm indexed (not so accurate the rpm range...)
you can say to the chip the max retard allowable vs. rpm in power enrichment mode.
rpm deg retard
6400 5.98
5600 5.98
4800 5.98
4000 11.95
3200 15.29
2400 10.90
1600 8.96
800 8.09
Knock retard in Power Enrichment table is rpm indexed (not so accurate the rpm range...)
you can say to the chip the max retard allowable vs. rpm in power enrichment mode.
rpm deg retard
6400 5.98
5600 5.98
4800 5.98
4000 11.95
3200 15.29
2400 10.90
1600 8.96
800 8.09
Last edited by conv90; Dec 22, 2005 at 05:43 AM.
