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Discussion Starter #1
Hello everyone,

I hope someone might be able to help me. I have been out of the Z car scene for a while and would like to get back. I have a 1975 280z with a stock European spec l28 Turbo engine. I parked it over a year ago because it had a very rough idle and it needed rear brakes. I got some cash together to do some work but the rough idle has gotten worse. I went through most of the components that this engine has in the US spec 280zxt service manual. I believe my problem is a bad knock sensor, I know this wouldn't normally cause a bad running engine, but I remember before when the terminal connection was corroded it ran badly like this. This also uses a knock sensor control module.

So my question is, would someone measure the ohms of resistance with a digital volt meter so I can check if mine is in range? I would really appreciate it. Mine is around 7k ohms.

Thanks,
David
MA
 

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The knock sensor is a piezoelectric device that sends an electrical signal to the ecu if there is excessive vibration. It will only function if the vibration is severe enough such as when the engine is detonating. It has no specific resistance or polarity. You can connect it "backwards" and it will not affect performance.

81zxturbo(labotomized with 300zx ecu and other stuff)
95slobaru
 

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I was reading about testing these the other day, they generate voltage when they are in normal use (seeing normal engine noise) and make more voltage when they hear a knock. The ECU looks for this threashhold to retard the spark. To test, hook up an oscilliscope to the sensor and tap on the engine block and see if you get a voltage reading. A digital VOM probably won't see this spike. Sorry I have no reference voltage to give you, maybe a net search will help you find some relevant readings?

Another down and dirty test is to run the engine with a timing light and tap the block near the sensor and see if the timing retards.

I'd be surprised if this was your problem but stranger things have happened with these cars!
 

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i have been running my'77 turbo with no knock sensor at alll (wires dangleing) and it rruns fine, as for the other, get a mega squirt, that is what i'm doing....
 

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A knock sensor is a microphone, for all practical purposes.

You want to see if it's working? atach it to an amplifier and listen with headphones..... if you hear your engine running but sorta like an underwater sound, then it's working.


And I do not believe a knock sensor can cause a rough idle, I've ran my ZXT with the sensor disconnected and it ran fine.....


I have one word for you

Megasquirt
 

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Discussion Starter #8
Thanks very much for everyone's input. If worse comes to worse I will have to get SDS or something similar, which wouldn't be a bad thing.

Thanks,
David
 

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No it wouldn't be a bad ing, actually would be the best thing you could do!
 
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