can it be done, i think the ecm's entire circut is a 5volt cicut. now i want to mount a ledlight that will flash when detionation is acuring. i dont however want to use the knock sensor the computer uses because i donot wish to damage/interfiere with its readings for this experiment, i was gonna grab a knock sensor from a junkyard 305 (should be the same thing as my 305tpi's) or if not get a new one, and wire one end to a 5 vold led and the other to a 5vold power source (have to convert 12-5) will this work? ahs anyoen done somethign simeler


-Stell

p.s. please excuse the spelling/grammer of this message, 2 things i amnot great at


------------------
1988 IROC 305TPI MINT!!
Mods= Accell SuperCoil, MSD 6A, Ported Plenum, No MAF Screans , K & N, 160 Thermostat+ Temp Switch
And Always Trying To Go Faster

 

hehe
yeah its possible but i think you want to use whats coming out of the esc which is basically the filter for what the knock sensor is reading which is everything.
dont worry about taking power from it since its really just a voltage signal an led meter wont decrease the voltage of it just draw a little current
ther is an article on the web on how to build one but i lost it

 

Well, I think you have s cool idea, but i wouldnt know how to hook something like that up... see the knock sensor just has one input wire to the ECM. The knock sensor actually produces an AC signal that goes directly to the ECM when knock occurs. The ECM takes this AC signal and figures out how much timing to retard. There is no wire you can tap into to have an LED light that I can think of...

oh yeah, on the 5 volts ECm thing.. The ECM uses 5 volt and 12 volt power, depending on the circuit.

 

I think you would need to install a 'monitor' that is wired parallel to the signal wire from the ESC going to the ECM. The monitor's job would be to measure the voltage. If it dropped below 6 volts for more than a set amount of time it would momentarily close a relay that lights up an LED and/or activates an audible alarm.

Mike

 

Actually, on my 89 the wire from the knock sensor goes to the ESC module (Electronic Spark Control) first, and a second circuit connects the ESC to the ECM on terminal B7 of the ECM. I believe that the ESC is essentially interpretting the signal coming from the knock sensor. If knock is detected, the ESC lowers the voltage being fed to the ECM below the 12 volts normally supplied under a no-knock condition. I think that the wire going to the ESC may contain an AC signal, but the connection from the ESC to the ECM should be straight DC.

 

yeah dale got it for us tbi or pre 90 tpi cars

hmmmmm now you guys have piqued my interest.. you could probably actually even wire this up to the same type of led meter that monitors air fuel ratio
just flip it upside down, when the leds go out upwards thats a bad thing
if it is infact as simple as what it sounds
i think im gonna put my dmm on the esc to ecm wire and tap the side of the block with a wrench see if it causes any whackyness



[This message has been edited by Pablo (edited September 10, 2000).]

 

From the helms service manual (thanks Dirk!)

"When the ESC sensor detects abnormal vibration in the engine, it produces a voltage that is received by the ESC module. As long as the ESC module sees no voltage from the knock sensor (knock not present), it send a signal voltage (8 to 10 volts) to the ECM and the ECM provides normal spark advance."

"When the module detects voltage from the knock sensor (knock present), it turns "OFF" the signal to the ECM and the voltage on CKT 485 goes to 0 volts. The ECM then retards EST to reduce spark knock."


AHAHAH ITS THAT SIMPLE!?! Jeez anyone can build a knock detector! im doing this ASAP.. ill probably just make an LED that lights up when voltage hits zero

 

The 5V circuit is used only on the Throttle Position Sensor, as a reference, and FYI, the fuel pump relay uses a 12V circuit.

The Knock sensor only produces Millivolts of electricity, I guess in theory, the only way to use this to your advantage would to wire inline a custom "interpreter" to read the knock counts and display them as a blinking LED. The ECM can do this, but it's only interpreted by a scan tool.

 

I stand corrected, I didn't know about the 8-10 volt ESC>ECM signal...

 

A circuit to monitor the knock sensor output is a little more complicated than the posts above would indicate. I believe that the output of the knock sensor comes from a piozelectric element which is put on top of a 5 volt reference signal from the ECM. This produces an electrical current when it is hit - the same principel is used to produce a spark (voltage) to ignite gas stoves.

Elsewhere in this web site, I saw a reference to a site that shows how to build a knock sensor indication circuit. Look at: www.gnttype.org/techarea/projects/projectspage.html Select "Circuit.GIF" for the schematic which is straightforward. Commonly available parts are used(Radio Shack, Digi-Key, etc.) which looks like it'll work to me. The input impedance should be high enough that it would not affect the ECM if it is conneted in parallel.

[This message has been edited by Stuart Moss (edited September 11, 2000).]

 

Stuart.. I understand trying to build a knock detector using the output of the actual sensor would be hard since its essentially a microphone and knock only happens at a certain frequency/amplitude, right?
but what i was looking at was the output of the esc to the ecm since the esc does all the deciphering for you and simply drops the voltage signal to the ecm when it detects knock. This is how i understand it to work according to the helms service manual. What is the flaw in this? just using for instance a DVM to see voltage drop indicating knock?
granted this wont work on cars with the esc module on the memcal or in the ecm but for those of us with the esc out in the engine bay why not?

 

hm mjust checked it out and they do use the output of the esc..