06 F250 TXR intermittent Check Engine message

[99yam40]

I have the feeling Bosco was trying to see if there was good or bad voltage at the ECU.
could be the wire or connections bad (high resistance) dropping the voltage down at the KS itself

[Nourse1168]

Alright heres the result..... First off, i bought a new Klein meter to rule out the old one and am seeing some different voltages now. I back probed the KS pin at the ECM,o and heres the numbers. With the sensor disconnected, I am receiving 4.6v. With the sensor connected, I am getting 2.363v. I believe these numbers are more inline with what it should be. Also, I checked the voltage with the replacement KS grounded to the block. I got the same number as the installed sensor. I feel like i am finally making some head way. Thanks again for everyones input, it is extremely helpful.

[boscoe99]

carefully look at the diagram.
you note a piezioelectric crystal shunted by a resistor.
there is a (voltmeter) inside the ECU that is measuring the DC voltage dropped by the resistor,when a knock is detected the piezio device sends an A/C signal riding on the reference.
it is always possible a different sensor is loading down the 5v ref.
they wont show us a circuit diagram inside the ECU.
I use a small MAR-PAPER-CL-IP to back probe the connectors.

I prefer alternate part number MAR-NEEDL-CL-IP myself.

[boscoe99]

Not my words. Yams. The head kahuna.

Knock Sensor
The knock sensor is a piezoelectric device (it generates a small AC voltage when subjected to certain
vibrations) The ECU provides a 5-volt reference signal to the knock sensor. If a knock
occurs, the knock sensor produces an AC voltage that “rides” on the 5-volt signal. The amplitude
and frequency of the AC signal generated by the knock sensor are dependent on the level of
knock.

[Nourse1168]

I think I am going to run the motor and test the AC voltage created by the KS. Yamaha tech told me I should BE seeing about (.8v-4.0v AC). anything outside of that would cause a timing change and set a code.. That sound right to you guys ?

[boscoe99]

Maybe it is MAR-NEEDL-EP-IN

[boscoe99]

Alright heres the result..... First off, i bought a new Klein meter to rule out the old one and am seeing some different voltages now. I back probed the KS pin at the ECM,o and heres the numbers. With the sensor disconnected, I am receiving 4.6v. With the sensor connected, I am getting 2.363v. I believe these numbers are more inline with what it should be. Also, I checked the voltage with the replacement KS grounded to the block. I got the same number as the installed sensor. I feel like i am finally making some head way. Thanks again for everyones input, it is extremely helpful.

I would not expect that much voltage drop.

[Nourse1168]

I rechecked KOhms on installed KS and the replacement KS with new Klein meter and both tested good.

[Nourse1168]

boscoe_ I read recently that the voltage drop on knock sensors should be about 1/2 of the source voltage which in my case is what Im getting. However, i am unsure if this is correct information. The voltage drop is the same on both sensors I have..

[rodbolt17]

ever hear of a small thang called Ohm's Law?
you have a known voltage and a known resistance. do a tad o math and you get the expected voltage drop.

[99yam40]

ever hear of a small thang called Ohm's Law?
you have a known voltage and a known resistance. do a tad o math and you get the expected voltage drop.

Rod do you think the 4.6 v is a good voltage at the ECU out without the KS hooked up.
I am not sure how far off the 5V reference should get under normal operations

[boscoe99]

Most Yamaha five volt output circuits maintain their output voltage plus or minus a few tenths of a volt when the circuit is loaded.

The specification for the sensor itself in ohms is 504 ~ 616 kilo ohms. 504,000 ~ 616,000 ohms. A hellava lot of electrical resistance. I would not expect that much resistance to allow that much current to flow so as to cause a multi volt voltage drop. But, I am guessing here. Yamaha does not offer any advice.

Which is why I suggested finding someone with your model F250 that will let you test their motor to see what is to be seen.

[Nourse1168]

let me check another known 5v reference and see what i get

[boscoe99]

Rod do you think the 4.6 v is a good voltage at the ECU out without the KS hooked up.
I am not sure how far off the 5V reference should get under normal operations

[Nourse1168]

bosoce, i just checked the engine temp, and shift cut sensor they both have 4.99v. But how can I verify the KS should have the 5v? I cannot find a reference to its voltage anywhere?