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I have tested all conecctions to the ESC. HOWEVER i am not getting any voltage from the dark blue wire to the knock sensor. I have read that it needs to be 5 volts. would the FEMALE plug/connector be bad (the one that plugs into the ESC). AGAIN, no voltage from esc to actual knock sensor
I wonder are you getting 12 v on the pink/blk wire which power the ESC. Mabey your dark blue has a break in it. Also I would clean the connector very well with contact cleaner(plastic safe),
Lasly the black wire sends the signal to the ECM.
I am getting 12v on the pink wire(B) at the esc from the battery. Getting 9.2 volts at the black wire(C) at the esc from the ecm. the brown(D) at esc is grounded. The dark blue wire(E) at esc going to knock sensor reads "0.0" and is not grounded. Chevythunder . com says that this wire needs 5v straight to the knock sensor. Is this not the case?
Dark blue (E) has no break in it. It reads 0.0 at the top right by thr ESC and 0.0 inside the connector that plugs into the knock sensor. Wire is good. Thats why i suspect it may the female plug? Where would the dark blue wire get power from?
I appreciate everyones time and responses. I dont have a manual at this time.
That's an AC voltage at the dk blu wire. Where did you get your info on the 5 v DC voltage?
The test procedure is in your FSM, under Electronic Spark Control (ESC) System Check. You do have one, don't you?
With the engine running at about 1500 rpm, tap on the side of the block near the knock sensor with a small hammer. The rpm should drop.
What's your problem? Most people don't test their ks just for the fun of it!
I am getting code 43 on dash. and running sluggish due to retarded timing from not being able to detect knock. Does the connector that plugs into the knock sensor need to have any voltage? right now it is reading 0.0 on my multimeter.
I would unhook the battery to reset the ecm, Then clean connectors on ESC and ECM(pinnes could be dirty and not recieving test signal), Then do hotrods tap test and see what happens.
If you need the manual I can post the 2 pages about it.
One other thing did you replace the knock sensor and put a bunch of tape on the threads to stop the grounf. Just wondering.
Good luck!
I would unhook the battery to reset the ecm, Then clean connectors on ESC and ECM(pinnes could be dirty and not recieving test signal), Then do hotrods tap test and see what happens.
If you need the manual I can post the 2 pages about it.
One other thing did you replace the knock sensor and put a bunch of tape on the threads to stop the grounf. Just wondering.
Good luck!
I really appreciate these pics! So after some trouble shooting, the SES light only comes on after the engine warms up to 195* and is under load. If i clear the codes by disconnecting the battery, the car runs fine until it warms up and is under a load. So the test on page 6E3-59 in your pictures is hard to trouble shoot bc the SES light will not come on with the engine idling. I have tried tapping the block and the RPMs do NOT DROP. So i believe i need to look at > no RPM drop> see section c-5 step 2. Is there any way you can post a pic of this step? Or would this be the knock sensor is bad? no sealant was applied to knock sensor but it is not an ac delco brand knock sensor. It was torqued to 14 lbs.
What has confused me is, the SES does not come on at start up or at idle..only under load at OP temp. So something is causing the volts at b7 at ecm (black wire at esc) to drop under the required 6 volts.
Also, have we confirmed dark blue wire at ESC should not have any voltage? Again, mine reads 0.0. Does the knock sensor produce any voltage to this wire?
I really appreciate these pics! So after some trouble shooting, the SES light only comes on after the engine warms up to 195* and is under load. If i clear the codes by disconnecting the battery, the car runs fine until it warms up and is under a load. So the test on page 6E3-59 in your pictures is hard to trouble shoot bc the SES light will not come on with the engine idling. I have tried tapping the block and the RPMs do NOT DROP. So i believe i need to look at > no RPM drop> see section c-5 step 2. Is there any way you can post a pic of this step? Or would this be the knock sensor is bad? no sealant was applied to knock sensor but it is not an ac delco brand knock sensor. It was torqued to 14 lbs.
What has confused me is, the SES does not come on at start up or at idle..only under load at OP temp. So something is causing the volts at b7 at ecm (black wire at esc) to drop under the required 6 volts.
Also, have we confirmed dark blue wire at ESC should not have any voltage? Again, mine reads 0.0. Does the knock sensor produce any voltage to this wire?
Going off memory here...
You will not see a code set for a disconnected knock sensor until 195 degrees... leaves 3 options...
The KS is like a microphone. The output of the KS is an AC signal.
Ok got it. So no power should be in the blue wire if it is disconnected from the knock sensor. With it connected to a good working knock sensor, there will be some AC signal.
I am going to replace the knock sensor again and report back
Ok got it. So no power should be in the blue wire if it is disconnected from the knock sensor. With it connected to a good working knock sensor, there will be some AC signal.
I am going to replace the knock sensor again and report back
There should only be an a/c signal if the sensor is actually detecting knock. It's a piezoelectric generator. But I don't know if the signal is actually measurable on a typical meter, even if tapping on the block. I think I mentioned this on a FB thread, but the Code 43 you're getting is supposed to be indicative of a KS circuit problem rather than a problem with the sensor itself.
I wanted to update everyone on this thread. I received my FSM. I recently purchased the 85 with 50k original miles on it.
Realized the Knock sensor produces its own signal when detecting knock. I was able to plug into a buddies SNAP ON with OBD 1 capabilities.
Scratching my head trying to chase the code 43. i replaced the knock sensor which forced me to change the coolant, new ESC module, new knock sensor connector. NONE of that worked.
Talking with an older GM mechanic he was saying the same thing as MATTHEWMILLER above me was saying. If the ECM doesnt see knock it will throw the code. He then asked what fuel i was using. I said " i usually use 93 in all my vehicles and been running it in the vette bc it has been sitting" He advised me to run 87 bc higher octane fuels cause less knocking..................
SURE ENOUGH the lower octane fuel (87) allows the ecm to SEE knock at closed loop and doesn't throw the code... Vette runs amazing..
I guess its a good thing i replaced some of the stuff and i was able to return the ESC module, so ill chalk all this up as routine maintenance...
Apparently we shouldnt run higher than 87 octane in these vettes?
I wanted to update everyone on this thread. I received my FSM. I recently purchased the 85 with 50k original miles on it.
Realized the Knock sensor produces its own signal when detecting knock. I was able to plug into a buddies SNAP ON with OBD 1 capabilities.
Scratching my head trying to chase the code 43. i replaced the knock sensor which forced me to change the coolant, new ESC module, new knock sensor connector. NONE of that worked.
Talking with an older GM mechanic he was saying the same thing as MATTHEWMILLER above me was saying. If the ECM doesnt see knock it will throw the code. He then asked what fuel i was using. I said " i usually use 93 in all my vehicles and been running it in the vette bc it has been sitting" He advised me to run 87 bc higher octane fuels cause less knocking..................
SURE ENOUGH the lower octane fuel (87) allows the ecm to SEE knock at closed loop and doesn't throw the code... Vette runs amazing..
I guess its a good thing i replaced some of the stuff and i was able to return the ESC module, so ill chalk all this up as routine maintenance...
Apparently we shouldnt run higher than 87 octane in these vettes?
In your opinion, why would my engine knock "less" with higher octane and throw code 43.
Code 43 is the engine advancing the timing and not seeing knock.
Higher octane fuel has less of a tendency to knock (that's pretty much the definition of octane).
A knock sensor is a microphone putting out a relatively low voltage signal. Anything in the circuit from the sensor all the way to the ecm could be at fault here. Bad connections, bad ecm, bad wiring, knock sensor not spun deep enough into the block...
Something in that circuit is causing the pcm to not be able to recognize knock. Might even be the pcm itself.
Mine has no problems advancing the timing enough to force knock with 93 octane.
Code 43 is the engine advancing the timing and not seeing knock.
Higher octane fuel has less of a tendency to knock (that's pretty much the definition of octane).
A knock sensor is a microphone putting out a relatively low voltage signal. Anything in the circuit from the sensor all the way to the ecm could be at fault here. Bad connections, bad ecm, bad wiring, knock sensor not spun deep enough into the block...
Something in that circuit is causing the pcm to not be able to recognize knock. Might even be the pcm itself.
Mine has no problems advancing the timing enough to force knock with 93 octane.
I've back probed and tested all circuit wires. Giving it a tune up this weekend as well. Do you think old/worn spark plugs could cause this? My buddy also has a remfg AC delco ECM for an 85 that i am going to try this week. Ill just switch my proms/memcal in. It's been driving me crazy, so im glad it hasnt thrown it with 87 octane.
I've back probed and tested all circuit wires. Giving it a tune up this weekend as well. Do you think old/worn spark plugs could cause this? My buddy also has a remfg AC delco ECM for an 85 that i am going to try this week. Ill just switch my proms/memcal in. It's been driving me crazy, so im glad it hasnt thrown it with 87 octane.
Plugs? Don't know... doubt it.
The pcm switch is a good plan... but I would look long and hard at any connectors between the pcm and the esc and the knock sensor and make sure the knock sensor is completely seated in the block.
I personally installed a new knock sensor. I was worried bc I read so many things to not over torque it. I torqued to 15 ft/lbs. other than that. I’ve checked all wires and everything is good. So I’m still stumped.
I personally installed a new knock sensor. I was worried bc I read so many things to not over torque it. I torqued to 15 ft/lbs. other than that. I’ve checked all wires and everything is good. So I’m still stumped.
Did you check the connections all the way back to the pcm?
If the KS circuit needs to see some knock to avoid throwing a code, maybe more static advance would give you the knock it wants to see with that 93 octane?
1985 KNOCK SENSOR/ESC question..
