How sensitive is the knock sensor?
Thread Starter
Team Owner
Joined: Nov 1999
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From: This vette goes to 11 Milford MA
St. Jude Donor '03-'05
How sensitive is the knock sensor?
On my 88, I think my headers/exhaust is rattling against the frame somewhere. Of course it will only do this in gear so its hard to find. Will this trip the KS?
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From: SE NY
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Re: How sensitive is the knock sensor? (Fastguy)
Rattles from exhaust, rockers and other sources can trigger the KS. It depends on the frequency; the KS is designed to respond to the range of frequencies around typical ping.
Advanced
Joined: Oct 1999
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From: East Sandwich MA
Re: How sensitive is the knock sensor? (Fastguy)
It is very sensitive, I would run Diacom to see if you are having any spark counts.
Smallblock(Andy D.) had problems with his 88 with false knock and he changed the knock sensor. Problem was solved, you can do the same by wrapping the sensor with tape to de-sensitize it.
Smallblock(Andy D.) had problems with his 88 with false knock and he changed the knock sensor. Problem was solved, you can do the same by wrapping the sensor with tape to de-sensitize it.
Melting Slicks
Joined: Apr 2000
Posts: 2,793
Likes: 46
From: Elizabeth City, NC
Re: How sensitive is the knock sensor? (shera)
I had problems with my knock sensor on the 90. It was picking up the roller rockers, headers, cam, gear drive and whatever else it deemed necessary. So when I had the chip made I had Shalin turn the knock sensor off basically. You can't really turn it off, but you can set it to do nothing when it sees knock so thats what he did.
Thread Starter
Team Owner
Joined: Nov 1999
Posts: 26,679
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From: This vette goes to 11 Milford MA
St. Jude Donor '03-'05
Re: How sensitive is the knock sensor? (LPDesRoche)
Well, its going on the dyno Saturday and I am contemplating running it with the KS unplugged. I ran my Turbo Tbird for years without one.
Former Vendor
Joined: Jun 2001
Posts: 7,204
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From: St Marys PA
Re: How sensitive is the knock sensor? (Fastguy)
Eeek! Unhooking it you are playing with death... I would kill myself if something serious went and I ruined my engine because of taking a short-cut like that. I would error on the side of caution when unhooking it. My car still gets counts even with the chip tuned pretty good. I too assume it is from the exhaust. I found one spot that the exhaust was touching the motor mount and causing sure false knock. Fixed it and it still does it. I also followed the tech tip advise of getting a new ECS. Still have counts. I have to start tuning for this warmer weather again. Most of the knock is when I force downshift and go WOT. At that instance many counts are experienced. I think from what I read that it is pretty natural. I may try to put tape on the knock sensor the next time I put it up for an oil change, but will definately advance the timing till knock is seen to verify that it is still able to detect and function. Good luck.
Le Mans Master
Joined: Oct 1999
Posts: 6,366
Likes: 34
Re: How sensitive is the knock sensor? (ski_dwn_it)
I believe if you unhook it, it will trigger an error code. Seems to me it would go into limp mode if this happens?
I have a resisitor on mine, with a switch. I use this for testing. the resistor by passes the knock sensor and the ecm does not know any different.
BTW, I had a cat hit a speed bump whcih pushed my air pipe which connects into the cat into my seat bolt in the tranny tunnel. I could not get it to rev over 2500 rpms, it was that bad. bent it out of the way and it ran perfect.
I have a resisitor on mine, with a switch. I use this for testing. the resistor by passes the knock sensor and the ecm does not know any different.
BTW, I had a cat hit a speed bump whcih pushed my air pipe which connects into the cat into my seat bolt in the tranny tunnel. I could not get it to rev over 2500 rpms, it was that bad. bent it out of the way and it ran perfect.
Burning Brakes
Joined: Feb 2000
Posts: 824
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From: Camden SC
Re: How sensitive is the knock sensor? (bill mcdonald)
Malfunctioning knock sensors can be fatal to an engine. When you have a "ping", the air/ fuel mixture is being ignited too early. The piston is traveling up and the "explosion" is sending it down. Opposing forces. Not good. Once ruined an engine (non vette) when the "slight" pinging (no knock senor on this engine) would occur under load. Two pistons collapsed over the rings and scored the cylinder walls, buy new engine. BUT IT WAS ONLY A LITTLE PING. Assuming you have a functioning knock senor and it picks up the bad vibes, timing is retarded in 4 degree blocks,(per second I think) When the vibes quit, the 'puter' starts slowly advancing the timing, believe 2 degrees at a time. In fact, damaging pings may not even be heard. Early detonations may not be audible but a functioning knock sensor will be detecting and correcting. Your senor will pick up vibrations long before our ears hear the ping. If your car is pinging, something is wrong. Seeing ring lands pinching a ring and scored cylinder walls is a significant emotional event. Oh yeah, the thousand dollars was also painful. Hope you have better luck.
dlmeyers 90 coupe zf6 3 speed shocks
dlmeyers 90 coupe zf6 3 speed shocks
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Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
Re: How sensitive is the knock sensor? (ski_dwn_it)
Fastguy & ski_dwn_it, you may be getting false knock counts. If so, try the ESC upgrade in C4 Tech Tips and on my site. Gordon Killebrew recommended it and it cured my false knock counts problem.
The ESC module, near the heater blower by the right fender pannel, was used on '85-'89 L98s. In '90-'96 the knock sensor output went directly to the ECM.
[Modified by 65Z01, 7:10 PM 4/11/2002]
The ESC module, near the heater blower by the right fender pannel, was used on '85-'89 L98s. In '90-'96 the knock sensor output went directly to the ECM.
[Modified by 65Z01, 7:10 PM 4/11/2002]
