Knock Sensor; What happens if its disconnected - ZR-1 Net Registry Forums

LGAFF · 06-29-2009

Could not get this answered on the other forum, if the knock sensor is disconnected does the ECM retard timing?

Kevin · 06-29-2009

no the ecm does not retard timing since it doesn't detect knock. disconnecting it does nothing positive for you and can only end up hurting, at least according to Haibeck

LGAFF · 06-29-2009

I did not disconnect, it was disconnected when I put it up to change the clutch. 101 projects for your corvette says it retards timing at WOT, when it is not hooked up.

If ECM does not detect resistance it retards a precaution...per the book. Checking to see if this is accurate.

Kevin · 06-29-2009

Quote:

Originally Posted by LGAFF

I did not disconnect, it was disconnected when I put it up to change the clutch. 101 projects for your corvette says it retards timing at WOT, when it is not hooked up.

If ECM does not detect resistance it retards a precaution...per the book. Checking to see if this is accurate.

this would make sense...my first post may have been wrong

XfireZ51 · 06-29-2009

Lee,

Looking at the FSM and reading the Diag Charts and reviewing of Code 43, the ECM only retards timing when it receives an AC signal produced by the KS. There's no indication that the ECM goes into a "default" timing if it doesn't "see" the knock sensor. If there's an open circuit, as in your case, then a voltage of either >3.62v or <1.44v will cause the ECM to set a code 43 after 24 seconds. I don't have an answer as to why you don't have a code set.
There's a second test the ECM will run under the conditions of Coolant at > 93C and High engine load. If the ECM does not see a response from the ECM, a Code 43 will be set. I also remember that the GN guys would pull the knock sensor connector to avoid KR (Knock Retard). Of course, the LT-5 ignition could be different but the GN ignition is close as it uses Waste Spark.

LGAFF · 06-29-2009

I guess we will find out when the clutch goes back on, I would think there would be some kind of protection for the engine in the event the wire came off.

-=Jeff=- · 07-01-2009

C'mon guys..

If you unplug the Knock Sensor.. then the Knock Sensor does not work

Starman · 08-07-2014

The ECM does check this circuit periodically by advancing timing to trigger spark knock and checks to see if the sensor detects it. I had a bad pigtail connector and was getting a code 43 about every other drive. Replaced pigtail with OE AC Delco part from Advance Auto Parts and no more codes.

06-29-2009	#1
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Knock Sensor; What happens if its disconnected Could not get this answered on the other forum, if the knock sensor is disconnected does the ECM retard timing? __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

06-29-2009	#2
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,632	Re: Knock Sensor; What happens if its disconnected no the ecm does not retard timing since it doesn't detect knock. disconnecting it does nothing positive for you and can only end up hurting, at least according to Haibeck __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

06-29-2009	#3
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Re: Knock Sensor; What happens if its disconnected I did not disconnect, it was disconnected when I put it up to change the clutch. 101 projects for your corvette says it retards timing at WOT, when it is not hooked up. If ECM does not detect resistance it retards a precaution...per the book. Checking to see if this is accurate. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

06-29-2009	#5
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,700	Re: Knock Sensor; What happens if its disconnected Lee, Looking at the FSM and reading the Diag Charts and reviewing of Code 43, the ECM only retards timing when it receives an AC signal produced by the KS. There's no indication that the ECM goes into a "default" timing if it doesn't "see" the knock sensor. If there's an open circuit, as in your case, then a voltage of either >3.62v or <1.44v will cause the ECM to set a code 43 after 24 seconds. I don't have an answer as to why you don't have a code set. There's a second test the ECM will run under the conditions of Coolant at > 93C and High engine load. If the ECM does not see a response from the ECM, a Code 43 will be set. I also remember that the GN guys would pull the knock sensor connector to avoid KR (Knock Retard). Of course, the LT-5 ignition could be different but the GN ignition is close as it uses Waste Spark. Last edited by XfireZ51; 06-29-2009 at 11:17 PM.

06-29-2009	#6
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Re: Knock Sensor; What happens if its disconnected I guess we will find out when the clutch goes back on, I would think there would be some kind of protection for the engine in the event the wire came off. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

07-01-2009	#7
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,161	Re: Knock Sensor; What happens if its disconnected C'mon guys.. If you unplug the Knock Sensor.. then the Knock Sensor does not work __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Flowmaster Cats - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

08-07-2014	#8
Starman Join Date: Sep 2008 Location: Speedway, IN Posts: 132	Re: Knock Sensor; What happens if its disconnected The ECM does check this circuit periodically by advancing timing to trigger spark knock and checks to see if the sensor detects it. I had a bad pigtail connector and was getting a code 43 about every other drive. Replaced pigtail with OE AC Delco part from Advance Auto Parts and no more codes.