So are there only two types? The 3.9 ohms and 100 ohm? Is that the only difference? If so, then the sensor ohms need to match up to the ESC? Is there list somewhere the clarifies which knock sensor goes with which ESC?

 

Funilly enough, I was just looking into this for my LT1. And in the thread, someone who worked for GM chimed in. I realize it doesn't really address your question as to which years used which resistance, but the reasons behind the change are interesting to know.

He explained it as the change from 100 to 4 was to allow the ECM/PCM to detect if the knock sensor was plugged in. And later they changed back to 100ohm because they found a different way to diagnose if the sensor was plugged in or not.

I know my LT1 uses the 4ohm. Which makes me think that with all the false knock I have, did I order the wrong sensor? I need to check.

Look for the posts from 69247 here: https://www.corvetteforum.com/forums...he-lt1-km.html

 

Pretty sure for an 89 you need to match it to the knock module, not the ECM, but you're outside my area of operation.

 

Thanks and yes, your are correct Drew, the module, not the ECM. I'll correct the post above.

 

On our 3rd gens, any EFI system that used an external knock module used the 100K ohm knock sensor. Starting in '90 the port injected 3rd gens used an internal knock filter. With these the sensor is a 3.9K ohm unit. While the '90+ TBI units using the external filter stayed with the 100K ohm sensors.

As posted the use of the 3.9K ohm sensors was so that the ECM ('7730) was able to read the knock sensor voltage for diagnostic purposes. The ECM provided a 5 V bias to the sensor via a 3.9K ohm resistor. So it was expecting something in the 2.5V +- range when all was OK.

Even at that there is a forced knock test that was also used. The ECM would crank up the spark advance (warm engine under high load) to force the engine to knock. Lousy idea as it was easily defeated by running premium fuel. Resulting in a code 43 and a lack of power due to self-imposed ignition timing retard.

Note that not all calibrations used the forced knock test.

RBob.