Knock sensor circuit operation?
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Knock sensor circuit operation?
Hello, I have a 1985 Corvette and I want to be notified when the computer detects a knock. Since my computer doesn't data log knock counts, I would like to do this with a light bulb hooked up to the knock sensor circuit in a parallel circuit.
Since the knock sensor emits a low voltage reading I assume, I believe it goes to the ESC module and then signaled out to the ECM, I would like to tap off the wire from the ESC to the ECM, if that's how it works. At this point I'm only making assumptions as I haven't seen a wiring diagram for it.
Can anyone provide a diagram or an explanation including wire colors and possibly terminal numbers for the knock sensor circuit?
Thanks a lot!
Since the knock sensor emits a low voltage reading I assume, I believe it goes to the ESC module and then signaled out to the ECM, I would like to tap off the wire from the ESC to the ECM, if that's how it works. At this point I'm only making assumptions as I haven't seen a wiring diagram for it.
Can anyone provide a diagram or an explanation including wire colors and possibly terminal numbers for the knock sensor circuit?
Thanks a lot!
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Here ya go:
My '86 FSM shows the knock sensor to ESC module wire as dark blue, so I don't know what's up there. For your application you don't care.
The pulses out of the ESC module are very short, so a light bulb wouldn't work. You need an LED with a relatively low value resistor. I would go with around 100 ohms. That should give you a flash that's bright enough to see.
Note that the ECM tests the ESC circuit by advancing the timing when you first start the engine, so you will get a couple of knocks at startup. The ECM will set an error code 43 if those knocks are NOT there.
My '86 FSM shows the knock sensor to ESC module wire as dark blue, so I don't know what's up there. For your application you don't care.
The pulses out of the ESC module are very short, so a light bulb wouldn't work. You need an LED with a relatively low value resistor. I would go with around 100 ohms. That should give you a flash that's bright enough to see.
Note that the ECM tests the ESC circuit by advancing the timing when you first start the engine, so you will get a couple of knocks at startup. The ECM will set an error code 43 if those knocks are NOT there.
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Here ya go:
My '86 FSM shows the knock sensor to ESC module wire as dark blue, so I don't know what's up there. For your application you don't care.
The pulses out of the ESC module are very short, so a light bulb wouldn't work. You need an LED with a relatively low value resistor. I would go with around 100 ohms. That should give you a flash that's bright enough to see.
Note that the ECM tests the ESC circuit by advancing the timing when you first start the engine, so you will get a couple of knocks at startup. The ECM will set an error code 43 if those knocks are NOT there.
My '86 FSM shows the knock sensor to ESC module wire as dark blue, so I don't know what's up there. For your application you don't care.
The pulses out of the ESC module are very short, so a light bulb wouldn't work. You need an LED with a relatively low value resistor. I would go with around 100 ohms. That should give you a flash that's bright enough to see.
Note that the ECM tests the ESC circuit by advancing the timing when you first start the engine, so you will get a couple of knocks at startup. The ECM will set an error code 43 if those knocks are NOT there.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
You're sure spending a lot of time with the 6870 that would be better spent with the 7165? Also, be careful when using the knock sensor to tune for spark. Larger cams and valve geometry can create harmonics that may be picked up by the sensor that are not detonation.
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I can't afford to go to the 165 at this time.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
I provided him a list of parts and the costs. When he decides to pull the trigger I'll be happy to provide the procedure I documented when I did mine. It took me the better part of a day to make the swap. The tuning has a much longer learning curve.
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5th Gear
Joined: Feb 2013
Posts: 5
Likes: 0
From: Peoria Arizona
My 85 also has code 43 issues!
I have replaced the knock sensor, the ESC, and the ECM.
The timing is set at only 4 degrees advanced and I run only premium fuel. The system is working because as soon as the check engine light comes on I can feel the timing retard. Please help
The timing is set at only 4 degrees advanced and I run only premium fuel. The system is working because as soon as the check engine light comes on I can feel the timing retard. Please help
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
You should start your own thread. Otherwise it gets confusing when the answers to YOUR problem get mixed in with the answers to the original poster's problem.
5th Gear
Joined: Feb 2013
Posts: 5
Likes: 0
From: Peoria Arizona