Knock Sensing and Knock Maps

chris2712au · Post by **chris2712au** » Sun Jul 20, 2008 6:43 pm

Does anyone know when the knock maps start to run ??? is it when the knock sensor reaches XXvolts?? if so what is XX or is it when the ecu senses a fault, O2 too lean etc...

Matt · Post by **Matt** » Mon Jul 21, 2008 2:41 pm

Starts using knock maps when knock sensor is disconnected or below valid resistance (KNOCK_SENSOR_DTC raised) or if there is excessive knocking detected

chris2712au · Post by **chris2712au** » Mon Jul 21, 2008 9:22 pm

as in below 2.5v or what knock level in nistune...

Matt · Post by **Matt** » Tue Jul 22, 2008 11:34 am

Knock count inside Nistune only works for HCR32 Skyline testing at this stage. I'm working at adding it to more vehicles once I get the auto patcher code able to inject the new routines properly

There is no knock sensor voltage reported by nistune. I dont know the trigger voltage for flagging the DTC code for knock

UNISA JECS · Post by **UNISA JECS** » Mon Jul 28, 2008 4:31 am

Matt wrote:Knock count inside Nistune only works for HCR32 Skyline testing at this stage. I'm working at adding it to more vehicles once I get the auto patcher code able to inject the new routines properly

There is no knock sensor voltage reported by nistune. I dont know the trigger voltage for flagging the DTC code for knock

I know that a voltage if ~1 - 1.5v will set a DTC code for knock in a S13 but it will not illuminate a check engine light.

I also know that the ECU supplys 5v to the knock sensor pin on the ECU without knock sensor scnnected, and with the knock sensor connected if everything is working properly i.e. not short to grounds good knock sensor the voltage will be 2.5v with key on engine off. The knock sensor has a resistance of approx 550M ohms.

I think the ECU monitors both voltages above and below this 2.5v reffernce depending on the frequency the knock sensor produces.

PL · Post by PL » Mon Jul 28, 2008 4:30 pm

I use a 10Mohm resistor to fake out the knock sensor on the bench (S13) and it gives around 3V. The ECU is happy with this value.

PL

chris2712au · Post by **chris2712au** » Mon Jul 28, 2008 7:59 pm

so you would say above 3volts then it triggers ? I am very interested in the threshold value... Can you read the value in nistune for the s15 in the knock sensing ?

Also Pete I am starting to play around with the Modulation signals on the boost settings and would be very interested in the trials you did with the scope... what raw value you put in and what duty cycle that related to ?

PL · Post by PL » Fri Aug 08, 2008 4:31 pm

Hey Chris,

The ECU will be looking at pulses from the knock sensor rather than a DC level. I suspect the 3V level is only used for DTC generation. ie: it looks at the DC level and if it's around 3V then it assumes that the knock sensor is basically functional.

I didn't take note of what values in the boost control tables relate to what duty cycle at the valve. I must play with this again some time...

PL

PL · Post by PL » Fri Aug 08, 2008 4:31 pm

Hey Chris,

The ECU will be looking at pulses from the knock sensor rather than a DC level. I suspect the 3V level is only used for DTC generation. ie: it looks at the DC level and if it's around 3V then it assumes that the knock sensor is basically functional.

I didn't take note of what values in the boost control tables relate to what duty cycle at the valve. I must play with this again some time...

PL

satanstinydevil · Post by **satanstinydevil** » Tue Aug 12, 2008 2:18 pm

I'm in a dilemma similar to this. I get a DTC knock sensor with no dash light, but no knocks are detected, leading me to believe that the harness is bad. I still have to test it with a multimeter and check it out. I don't feel safe using a resistor

PL · Post by PL » Tue Aug 12, 2008 2:28 pm

I don't feel safe using the factory knock sensor...

PL

UNISA JECS · Post by **UNISA JECS** » Tue Aug 12, 2008 3:18 pm

satanstinydevil wrote:I'm in a dilemma similar to this. I get a DTC knock sensor with no dash light, but no knocks are detected, leading me to believe that the harness is bad. I still have to test it with a multimeter and check it out. I don't feel safe using a resistor

9/10 its gonna be a short to ground in the signal shielded wire, I have fixed about six S13 240SX KA24DE with this problem and they all shorted to ground within 1 foot of eachother on the wiring harness everytime.

You might find these links helpful:

http://www.sr20forum.com/calumsult/2353 ... ensor.html

http://www.sr20forum.com/general-sr20/2 ... -junk.html

PL · Post by PL » Tue Aug 12, 2008 3:45 pm

That idea about recording the signal from the knock sensor is very interesting. I might have to give that a go myself.

I've now been caught out several times by the ECU jumping to knock maps with SR20's. So much so that I have completely lost all faith in the factory knock sensing. Twice the engines were running stock boost, good mixtures and mild timing. There is no way in the world they were really knocking. There was no DTC coming up.

I now turn knock sensing off when tuning - and I've even started to leave it turned off permanently.

The area in the maps where knock is active makes it pretty much a waste of time anyway.

PL