Resistance value of knock sensor?

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BALDYMONSTER
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Resistance value of knock sensor?

Post by BALDYMONSTER » 12/09/19 12:24

I don’t suppose anyone knows what it would be?



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Re: Resistance value of knock sensor?

Post by shinny » 12/09/19 16:25

BALDYMONSTER wrote:
12/09/19 12:24
I don’t suppose anyone knows what it would be?
Don't you have a mk2 turbo? This topic is in the mk3 section...

Anyway, this is the testing instruction from the 3s-ge engine manual because that's what I had easily to hand. I doubt it would be different for a 3s-gte.

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Re: Resistance value of knock sensor?

Post by martin42006 » 12/09/19 21:48

if you want to test a knock sensor you really need an oscilloscope. but a basic if it has continuity/short circuit then that will tell you if its totally knackered.
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Re: Resistance value of knock sensor?

Post by MR2DI4 » 13/09/19 1:03

The knock sensor is a Piezo ceramic element like you have inside your watch that makes the beeping sound when you apply an small AC Voltage to it. The reverse applies if you shock it, it produces a small Voltage due to the "Piezo Effect".

They measure open circuit and do not need power on them for it to work. Never connected one to my scope but if you did and then tapped it lightly with a solid object you should see Voltage spikes on the scope. Obviously when these spikes exceed a certain limit, the ECU knows you have pre-detonation. I suspect that with age and heat that these old knock sensors just instantaneously fail if they actually experience a severe knock condition. The old sensor has been relaying just the "Normal" firing shock from each and every cylinder for years so you can imagine how may pulses it has generated.

Pointless putting in a second hand one, they are all pretty much stuffed the second you hit an actual knock condition for an extended amount of time and its definitely not worth putting in a new one either until the problem is resolved first.

I also understand the Torque applied to tighten these up is important as it effects the energy transference from the block to the sensor. The ECU clearly throws a check light if it doesn't see the pulses of an amplitude within a preset "Range". Too low it thinks the sensor is dead, too high and it thinks you have knock. Either way you get an Engine Check light.

An aftermarket sensor may or may not work depending on its design and output Voltage. Your best option is a genuine Toyota one which I imagine is expensive.

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