Disconnecting Knocksensor

[NMK]

Hi there,

I like to change my knocksensor to a piezo type unit.
I am wondering, what the Nistune is going to do if i simply unplug the old knocksensor? Will it always stay in the save fule map?

[alanjuggler]

if you remove it, put a resistor from the knock circuit to earth - the ECU will read it as being there and it won't flag a DTC.

i had problems with mine (not with nistune but an OEM chip remapped) not running quite right with the knock sensor unplugged even though my knock fuel and knock timing maps were direct copies of my main maps.

[NMK]

many thanks!

I will do so!

[skyshack]

There is a 2nd knock strategy somewhere in ECU.

I'm not even sure a Euro ECU program switches to the 2nd map, that could be a JDM only thing.

If it knocks on the low octane map (or any map for Euro) it does what it says in the manual EF&EC-17, it retards the ignition. Somewhere in the ECU "maps" there will either be a single drop dead retard value or a short table (8 values) v's rpm.

ECU doesn't use max retard if knock sensor fails. The lack of the sensor impedance allows all the stray electrical signals in the engine bay loom to induce voltages in the wire that are detected by the ECU as DET. Putting a resistor to earth on the plug terminal grounds the wire and prevents the induced voltage.

[raddy.]

If knock sensor DTC is present, EDM ecu will retard timing against hi octane map regardless any eventual signal activity at the knock link. This retard occnre at specific rpm/load range,roughly from 2500rpm to 4000rpm at full throttle. Before and after it follows timing map values. AFAIK EDM ecu will never use low octane maps. This DTC should be avoided to prevent hesitation in mentioned area at full thr.

[NMK]

Cheers for the help guys! But could you please explain me this bit in more detail please?:

The lack of the sensor impedance allows all the stray electrical signals in the engine bay loom to induce voltages in the wire that are detected by the ECU as DET. Putting a resistor to earth on the plug terminal grounds the wire and prevents the induced voltage.




I was reading the manual and I got to know that our knocksensor is giving voltage impulses using piezo electric elements.
I am under the impression, that the knocksensor has no ground. Hence I am unsure how the ECU is realizing that there is no sensor connected.
Is the ECU checking if small (non DET) signals are getting through to the ECU once the engine is running?

[raddy.]

ecu is measuring impedance of knock sensor circuit to know presence of it.

[NMK]

does it do it before cranking or does it do it while running?

[raddy.]

ecu do check before engine start or during crank, Im not 100% sure. But once is this DTC present and you reset it,it comes on again after next start. I never tested if ecu retard timing if DTC was resetted (but knock sensor is still missing).

[NMK]

But once the engine is running (with no knock sensor) with resetted DTC, the DTC will not come up again unless you stop the engine and start again, right?
That is good! This means i have not to fake a signal!

[raddy.]

yes,its like you described it.
But to be sure,you should test this,its some time past I played with this DTC and maybe I forgot some details.

[skyshack]

If i disconnect the lambda will it still fuel safely? I assume it will just read off the MAF?

Early cars (pre-facelift) didn't have a lambda sensor but a mixture screw that never needed touching. With the lambda sensor disconnected and the ECU reset it will work exactly the same as those early cars on the base mixture setting. The lambda sensor is for emissions, the catalytic converter won't work unless the mixture is very close to Lambda=1. It can be damaged by excessive heat from a very lean mixture or fuel burning in it from a very rich mixture.

For the CA the lambda doesn't work over 3200rpm at all. Below 3200 rpm it doesn't work at high load. Full range Lambda operation was introduced on the SR. Only the blue cells on the load/speed fuel map use lambda closed loop.



The lambda doesn't work at idle (idle switch).

It doesn't work when cold (about 2-3min).

What does your county's emissions test require?

Unlike most other Nissans Euro CA18DET doesn't have a "knock" map in the ignition timing map.