Felix

Any ideas what the format of the knock signal is on pin 11 of the 993tt's OBD connector? I'm guessing it's a 5v pulse?

Kevin

Time to get out the scope and run a trace.

jmayzurk

I don't have the answer, but I do have a scope with logging capability. If no one else knows the answer, remind me and I'll record it for you. God knows I can activate my knock sensors with the 91 octane **** we have down here...

Bill Verburg

The knock sensor signal is a filtered analog trace, under normal conditions the amplitude is close to zero

Felix

Thanks Bill but that's the sensor itself and there are two of them so I'm assuming the ECU is doing something with those signals to interleave them and "present" them on pin 11 in a meaningful format.

And thanks Jeff, if you get really bored please do have a play with a scope. I'll try using the DL1 as it has frequency inputs so should be able to count 5V pulses.

Bill Verburg

I don't have the OBD2 88 pin connector info handy, but on the 55pin OBD1 connector.
Pin 11 & 29 get the raw signal from the bridges attached to the cylinder head.

the signal is processed in the DME

the DME can correlate the knock signal w/ the flywheel position and cylider fioring infor to retard the ignition of the respective cylider in 2.25* increments to a mx of 12*

if the 12* max retard is insufficient then the DME tells the boost pressure controller to reduce boost

if knock ceases then ignition is readvanced incrementally to optimum setting

jmayzurk

Anyone have pin assignments for the OBD2 connector?

Felix

Here's a thread with the pin numbers of the OBD II connector on the console

And's heres the pinout:

Bill Verburg

Oh, I see now. You are talking about pin 11 on the diagnostic socket, not on the main harness from the engine to the DME

Felix

yup; sorry if that wasn't clear

IainM

Hi, found this in a search. Any conclusions on this?

I was thinking of putting something together along the lines of a Geiger counter that would give feedback to the knocking level.
TIA