About that knock sensor...

Ok, I'm just getting curious here - the knock sensor in my '93 SC2
controls the ignition timming to prevent ping.. How on earth do I know
if the sensor's working? I'm not getting any trouble codes, but that
really doesn't mean much. And I'm getting lousy mileage that i still
can't figure out

But it hit me the other day - the car also doesn't ping on hills
occasionally like it did when new. So, I'm starting to think here -
what if that sensor's acting up. Enough to cause the engine to retard
the timming, but not enough to turn on my Check Engine Light.

Oh yeah, and the car is high on the HC's when it goes in for a smogging.

I'm starting to wonder - maybe the sensor's constantly nagging the
computer about a ping that's not there?

Any ideas, guys?

 

You tap on the side of the block near the sensor and see if you get a
signal or see if the timing retards.

 

Ahhh, now, how do I measure engine timming changes?

 

Well thats the thing. I've almost always had access to scantools and
looked off of them. However, when you tap it and you hear a change in
the engines rpm it might be retarding the timing.

 

Hmm. I could plug my oscilloscope into it, if I knew where. I have a
timming light but I don't think it'd be too useful since the timming
seems to jump around anyway. Though i think that's just the pulley
bouncing. I'll try that first though if I can.

Has anyone heard of a sensor failing in a way that it'd cause the engine
to retard the timming, yet not turn on mr trouble light?

 

It's said that other noises can make the knock sensor respond. One example
given is a squeaking belt or idler pulley. The sensor "hears" that and,
mistaking it for a knock, retards the spark. Listen around the engine
compartment for unusual noises.

A scan tool is probably the best way to detect retarded spark. It will also
tell you other things that could be just as significant as spark.

Bob Henry

 

I'm not sure if they retard timing if they fail but they can fail
without turning on the MIL. Actually that might be possible... I havent
fooled with knock sensors in some time. But you should be able to tap on
the block next to the sensor and hear a audible change in the engine as
it adjust timing.

 

I could see possible scenarios where it COULD do it. i.e. it's got the
engine convinced you're pinging all the time or whatnot.

This motor for quite a while now has almost NEVER pinged, even in
places/situations where it used to when new.

And, retarded timming suggest bad mileage to me. And maybe high HCs.

I know nothing about them, other than they're supposed to be like a
microphone. There is a squeaky pulley on the car, but I can't figure
out which one it is

I'll try that. I don't know how I can get near it easily, though.