can someone tell me the signs and symptoms of a bad knock sensor. my sons car is acting up lately and I think its either the knock sensor or the computer. the car runs great 99% of the time, then for no reason will start running like crap !!,missing spitting,sputtering,and shaking. this happens at part throttle or at idle, it doesn't matter. also when this happens the exhaust mainfolds and pipes get REALLY HOT, and then starts belching black smoke from the tailpipe, then die. sometimes it will start right back up and run great or sometimes it won't start up, or sometimes it will start up but still run bad,I think the computer is retarding the timming too far, would that cause these symptoms ???

I have already checked or replaced all the obvious things (fuel filter,plugs,wires,cap,air filter,02 sensor,tps voltage,fuel pressure,etc,etc,etc,), now I am into the less obvious things.

the car is a TBI car

 

You can temporarily install a 3.9K ohm resistor in place of the detonation sensor to test your theory.

 

I believe the '86 takes a 100k ohm knock sensor.

 

A bad ignition module can cause some pretty weird symptoms.

Have you checked the coolant temp sensor(CTS). If it was reporting a cold eng to the computer, computer would increase the injector pulse width and eng would run rich. (I've seen a lot of the CTS elec connectors fall apart after they were 10+ years old)

Could the fuel press regulator be intermittently sticking and providing too much fuel press then free themselves up when eng died? Just a thought..