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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? |
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#3
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Ahhh, now, how do I measure engine timming changes?
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#5
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In article >,
Blah blah > wrote: > 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? |
#6
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"Philip Nasadowski" > wrote in message
... > 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? 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 |
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#8
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In article >,
Blah blah > wrote: > I'm not sure if they retard timing if they fail but they can fail > without turning on the MIL. 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. > Actually that might be possible... I havent > fooled with knock sensors in some time. 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 > 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'll try that. I don't know how I can get near it easily, though. |
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