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Knock Sensor Low Voltage


kxri318

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I've got a 1986 Ford Ranger 2.9 A4LD and got a knock sensor code. I checked the voltage at pin 23 on the ecu as shown in this connector pinout here: http://www.auto-diagnostics.info/ford_eec_iv and got only about 250mV when the truck was running when the diagram says I should be getting about 3v when running. If I unplug the sensor and then turn the key to the run position (but truck isn't running), I measure a very steady 2.575v. What would the voltage being about 250mV only when the sensor is plugged in point to? One thing that probably doesn't help is about 1/8" of the insulation on the ground side wire of the sensor connector is stripped away, but the wire looked great with no corrosion (It was also caked in oil which probably helped seal the wire off lol)
 


franklin2

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When you were pulling the codes KOER, did you do the goose test? You should have hammered the throttle when it told you to and brought the rpms over 2000. That is when it looks at the knock sensor for a response. If you did and still get the code, run the test again and when the goose test comes up, take a hammer a lightly tap on the exhaust manifold and see if the code goes away.
 

kxri318

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When you were pulling the codes KOER, did you do the goose test? You should have hammered the throttle when it told you to and brought the rpms over 2000. That is when it looks at the knock sensor for a response. If you did and still get the code, run the test again and when the goose test comes up, take a hammer a lightly tap on the exhaust manifold and see if the code goes away.
Yeah I floored it for a split second when it told me to and that test was when I got the knock sensor code. So when you say to tap the exhaust when the goose test comes up, do you mean to do that instead of the goose test or right after the goose test?
 

franklin2

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Yeah I floored it for a split second when it told me to and that test was when I got the knock sensor code. So when you say to tap the exhaust when the goose test comes up, do you mean to do that instead of the goose test or right after the goose test?
Tap instead of pushing the throttle during the goose test. You may get another code saying the engine didn't go beyond 2000 rpm, but see if you still get the knock sensor code. Tapping on the exhaust manifold should be enough for the knock sensor to hear it. If you still get the code, the wiring or the sensor must be bad.
 

kxri318

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Tap instead of pushing the throttle during the goose test. You may get another code saying the engine didn't go beyond 2000 rpm, but see if you still get the knock sensor code. Tapping on the exhaust manifold should be enough for the knock sensor to hear it. If you still get the code, the wiring or the sensor must be bad.
Ok thanks, I'll try that tomorrow and see what happens.
 

RonD

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Test Knock sensor with OHM meter setting, 2,000 to 3,000 ohms is expected

Some Knock Sensors are one wire, they are grounded to the block to complete the circuit
If yours is two wires then one wire goes to pin 23 and the other to pin 46 on computer
Pin 46 is the common "ground" for most of the other sensor

Also to test if any knock sensor is working let warmed up engine idle
Then tap the head, metal intake or block with metal bar or ??
RPMs should change when the computer "hears" the metal on metal "knock"
It changes spark advance
 

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According to the code book i got with my code reader it says to ignore a knock sensor code if the truck isnt pinging
 

kxri318

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Test Knock sensor with OHM meter setting, 2,000 to 3,000 ohms is expected

Some Knock Sensors are one wire, they are grounded to the block to complete the circuit
If yours is two wires then one wire goes to pin 23 and the other to pin 46 on computer
Pin 46 is the common "ground" for most of the other sensor

Also to test if any knock sensor is working let warmed up engine idle
Then tap the head, metal intake or block with metal bar or ??
RPMs should change when the computer "hears" the metal on metal "knock"
It changes spark advance
Sorry for being a day later than I said I would be, I got off late from work yesterday. Anyway, I tested for resistance and got overload on my multimeter. I also got a big wrench and lightly knocked on different parts of the engine and it didn't change anything about how it ran. Also, I made sure to warm up the truck before doing that test too.
 
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