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Discussion Starter · #1 ·
Folks-

Anyone know of any tests for a good/bad knock sensor (stock '85 5MGE), with the motor out of the car?

On my rebuild (which I'll get back in the car one of these days when family health issues return to a more normal state), the knock sensor is literally the only sensor on the engine that I did not replace with brand new Toyota parts (actually, new factory parts thru-out the rebuild).

However, I think I am gonna go ahead and replace the knock sensor as well, but was wondering if there are any known tests for verifying whether a knock sensor is good or bad. Mine is the factory original knock sensor and, to my knowledge, was working when I pulled the motor for the rebuild.

I found the following in a search, posted by "Dave A." on 9-6-04:

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"You can check the knock sensor by tapping on the block near the sensor with a small hammer. Hook up a timing light w/o shorting the check connector and aim the light at the timing marks with the engine running. The timing should retard as you tap the block with the hammer. 8)"
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As you can see, his suggested test requires the engine installed and running; I'm looking for any tests that can be done with just the sensor itself, if in fact there are any (above and beyond just a simple continuity test). I'm not sure of the exact internal components of the sensor, which makes it difficult to know what/how to test the unit.

Any direction(s) welcome.

Thanks,

Earl
 

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Earl, I was tied up with a little thing called accelerator pedals today...will try to get back to you in the morning. I'm unaware of a test for knock sensors without the engine management system up and running.
 

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Discussion Starter · #3 ·
Earl, I was tied up with a little thing called accelerator pedals today...will try to get back to you in the morning. I'm unaware of a test for knock sensors without the engine management system up and running.
Hey Mark, no prob man. I hesitated before I sent the parts inquiry figuring you were probably up to your eyeballs in the accelerator pedal 'situation'. I was suprised I got the price response back from you so quick (but that's pretty typicaly of ya anyway!).

Just thought I'd post the request here to see if anyone had any thoughts/ideas. I just don't know what the exact mechanism is inside the sensor to even begin to appropriately test it 'off' the motor.

Like I said, I'm probably gonna just replace it (I've replaced all else on the motor...kinda silly not to replace this sensor, too), but was just curious IF anyone knew of any 'off-the-motor' diagnostics on the unit.

Thanks again,

Earl
 

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Knock sensor should generate a current without Electronics hooked up. Hook up a lead, screw it into some kind of jig, tap/knock/pound on the jig, it should generate a (faint) voltage signal. Let us know if it works, Ive never actually done it.....
 

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I think it works like an heavily insulted Microphone. Kinda like a stethoscope a Doctor uses. If you have a few others, you could do like CarFreek suggested, but with more than 1 of them and see if they give the same resistances without banging, and then what happens when you do tap them.
 

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I thought it was a piezoelectric crystal-A crystal that gives off a voltage when it vibrates-crystal size/shape would determine what harmonic they "ring" at, and what voltage curve is produced. Anybody ever build a crystal radio?
 

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I thought it was a piezoelectric crystal-A crystal that gives off a voltage when it vibrates-crystal size/shape would determine what harmonic they "ring" at, and what voltage curve is produced. Anybody ever build a crystal radio?
No, I think I'm too young for that. Heh
 

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Discussion Starter · #8 ·
Knock sensor should generate a current without Electronics hooked up. Hook up a lead, screw it into some kind of jig, tap/knock/pound on the jig, it should generate a (faint) voltage signal. Let us know if it works, Ive never actually done it.....
Thanks, might be worth a try. I had no real idea what made up the actual 'mechanism' inside the sensor, so that info was interesting and helpful.

Not sure how easy it is for these particular sensors to fail, but this my '85 factory original, so it could be 'kaput' for all I know (and for all I know it was working fine when I pulled the motor for the rebuild). But, I've replaced all other sensors but this one, so it only really makes sense to go ahead and replace it too, but I thought, just for personal interest if no other, that it might be good to learn how to test them (off the motor) if, in fact, there is an 'off motor' test for them, other an a continuity test.

I'll post back what I find, when I get a chance to try those suggested tests.

Thanks again,

Earl
 
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