This is the problem. I just had my motor rebuilt,(95 lt1) I had a 224/236xe cam put in and forged pistons. After you start the car the ses light comes on after about 3 seconds. With it on the scanner it shows knock only at idle, so the computer advances the timing. With even the smallest amount of pressure on the throttle the sensor shows everything is fine and the timing goes back to normal. The mechanic told me the knock sensor is out of a 454 marine motor. He told me the frequencys were correct. Can you use a different sensor like that? When you drive the car and stop at a light the idle seems to go down to about 500 then you feel the timing advance and the idle goes up to 900 or so. The mechanic and I are both totally confused about this. I have an lt4km. Any ideas would be great to hear. Thanks

 

GM used two different impedance knock sensors on the LT1, so who knows what they used on a 454 marine engine. The OBD-1 KS should have a resistance of about 4,400 ohms. Make sure you have +5 volts at the connector, key to "on", engine off, harness connector off. With the connector still off the sensor, check the resistance from the single pin to the block. Should be 4.4Kohms. Then put the connector back on the sensor, probe the single pin on the sensor to the block and it should read +2.5 volts.

Since the sensor is basically a "tuned" piezo microphone, it is conceivalbe that different sensors from different engine are "tuned" to different frequencies. Makes no sens to just slap in the sensor from another engine.

 

Thanks for the numbers, I am going to test it tomorrow. Any Thoughts on what my problem could be other than the sensor?

 

Yes MAP sensor reading low/high at idle. Mine did it as well as another car. You may have to bump up your idle just a bit.

Did you pull the actual code?

 

I think the code was 43 or 47. Which ever one is the knock sensor.

 

Then I would get the proper KS (OBDI) and go from there.