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?

Re: False Knocks...where to look?
 

I would check the circuitry to be sure everything you have currently is in good shape. The KS should read 3300 to 4500 ohms from the contact pin to ground. If it's higher it may not be grounded to the block through the threads well enough. If it's lower in resistance, it's shot. You can assume since you don't have an SES, the wiring is not cut, grounded, or shorted to voltage.

The next thing you might consider is purchasing the less sensitive LT4 KM(PN. 16214681). I believe it was used to compensate for the LT4's roller rockers that the LT1 didn't have. It's only $32 and change from GMpartsdirect.com.

A few other things to consider. Did PCMforless program for the stock injectors or the LT4's which were 28#ers. GM found the 24#ers couldn't keep up with the LT4s demand and changed to the bigger ones. Now if your 93 Vette is like the 93 F-bodys, they where 22#ers and batch fired. Possibly making for an even worse problem.

Also, the top compression ring was changed on the LT4 due to a problem with high speed blowby caused by ring flutter. Your LT1 bottom end (with how many miles on it?) doesn't have that style ring.

Re: False Knocks...where to look?
 

He has a 93. There is no place to plug in an LT4KM on a 93 ECM.

Re: False Knocks...where to look?
 

IF you have a good tune on the car I say turn the thing off.

Re: False Knocks...where to look?
 

Desensetize or bypass.

Re: False Knocks...where to look?
 

Damn shame I'm not more formiliar with 93's. Didn't know they didn't have a removable KM. My F up. Always thank the person for pointing out my foible. :bow: But aren't Y body's 1 year ahead of F bodys?

Re: False Knocks...where to look?
 

Will check on the resistance.

[/QUOTE]The next thing you might consider is purchasing the less sensitive LT4 KM(PN. 16214681). I believe it was used to compensate for the LT4's roller rockers that the LT1 didn't have. It's only $32 and change from GMpartsdirect.com. [/QUOTE]

Unable to run the LT4 KM in the 93s.

[/QUOTE]A few other things to consider. Did PCMforless program for the stock injectors or the LT4's which were 28#ers. GM found the 24#ers couldn't keep up with the LT4s demand and changed to the bigger ones. Now if your 93 Vette is like the 93 F-bodys, they where 22#ers and batch fired. Possibly making for an even worse problem.[/QUOTE]

I left the stock ones in...I guess 22#.

[/QUOTE]Also, the top compression ring was changed on the LT4 due to a problem with high speed blowby caused by ring flutter. Your LT1 bottom end (with how many miles on it?) doesn't have that style ring.[/QUOTE]

Do you know at what rmp they had this problem? I'm only getting the knock counts between the 4900 and 5100 rpm. The rest of the upper rpms has no counts, but I'm not sure if the pulling of timing is helping to the no counts in the rest of the upper rpm. The car and engine currently has 16.3K miles on it.

Re: False Knocks...where to look?
 

The sound made internally in the headers is enough to do it and your RR's.
Turn the knock sensor off by puting it on a switch,then ya can have it or turn it off.

Re: False Knocks...where to look?
 

You can't interrupt the signal wire by "putting it on a switch". The PCM will interpret this as an open circuit, set a DTC and pull timing until the wiring is fixed or in this case, the switch is set back to the closed position. Thus accomplishing nothing.

Re: False Knocks...where to look?
 

Unless you have use a double pole Toggle and have the other side connected to a resistor