cfc928gt

So when the knock sensors detect knock and retard the timing by 6 degrees how much horsepower and torque are lost?

Vilhuer

According to one S4 dyno test, from 320 to 285 hp and 430 to 400 Nm at crank.

cfc928gt

Wow! Almost 6 hp and 5 tq per degree. That's pretty significant.

Jim bailey - 928 International

Yes it has much to do with how an engine accelerates....

John Speake

Correct - so there are trwo scenarios

1) knock sensor or Hall sensor fault - autotmatic retard of 6 degrees at high load/rpm

2) Detonation knock which steps back the igntion on the affected cylinder(s) up 9 degrees as described above. This is quite fast acting - but the recovery time is quite slow, several seconds. The recovery step size is small.

The system can identify which cylinder is knocking.

Chuck Schreiber

John,

After we did the TBWP job, the GTS seemed to be down on power.

Pretty sure we disturbed the knock sensor connection at the driver side front. Looking at it, it is toast. Absolutely looks like there is no connection beeing made there. This would explain the way the car pulls (less) to a certain extent correct???

Any way to do a temporary fix on this connection before we pull the intake to refresh in the next few months???

Thx!

John Speake

It will certainly reduce the power noticeably at medium to high loads and rpm.

Assuming the actual sensor is undamaged then you should be able to reconnect the wires in a temporary way by using the colours shown in the WSM wiring diagrams. To do a better job, Roger stocks the 3 way male and female connectors required.

GregBBRD

Plug in a good knock sensor, for the time being?

John Speake

Do you know if that would work, Greg ? I suspect not, as the knock sensor would not be sending plausible signals to the EZK.

But I've nver tried it....

brutus

If this is true..
"Most knock sensors send a base or “no
knocking” reference signal to the PCM.
If knocking occurs, the sensor detects the
increased vibration and increases its signal
to the PCM. ...."
And IF the 928 sensor does send a base signal you might need to attach the sensor to the engine somewhere so it sees background noise to work. Might be interesting to try it out some time.

Chuck Schreiber

So Greg,

You are saying just plug a good one in at the connector? Zip tie it up and I'm good to go??

It's just the knock sensor side that is toast not the wiring harness so theoretically I could do it. Would the knock sensor just be sensing "nothing"/ ambiant air temp underhood and work properly??
As long as it didnt sense detonation I guess I'm good to go???

I'm not talking about driving around like this for a year or 2, I'm just thinking a temporary fix until I have time to get the job done in the next month or 2.

I"m open to expert opinion, just want the car to run better until I can do a proper fix.

Thoughts???

Thx!

Chuck Schreiber

Roger that.

Again, I'm not trying to Jerry Rig this thing long term by any means, just a temp fix.

Thx John!

brutus

It might need to be attached to the engine for the background noise, might not. But probably would get enough vibration just about anywhere on the engine.

GregBBRD

I've plugged knock sensors into the systems to test, without doing anything special. I would think that the EZK is just looking for a "knock signal" above a certain threshold. Below that level, I'm not sure that it is "smart enough" to know that the knock sensor is "too quiet". However, certainly John Speake would know more about this, than me.

Speedtoys

What signal other than 'im here'..its just a microphone..of sorts.