trophy

The DME has some algorithm that looks after the filtering, how it filters is the unknown.

The OBD port output from the DME is what the DME referes to as "Knock Yes/No" on the wiring diagram, it does not tell what cylinder or what the DME does with it. The DME can calculate the Knock at the individual cylinder level based on the timing of the Knock relative to the revolution of the engine.

IXLR8

It would be cool to see the pseudo-code/program. This is a fun thread. Doing some digging, I came across the data sheet for the knock sensor 0 261 231 118 in our cars...file attached.

Steven, have a look at my comments I added in my last post. Your comments?

trophy

I think this comes down to significance, i doubt the event shown on the graph was significant enough for the ecu to retard the timing, therefore just would be ignored. The big question is, is it significant enough to do something about it? ie different fuel or changing the ignition timing. If you look closely to the graph you can see lots of little dips in the graph, the 'Knock yes/no" could be counting these and this is what Eric saw when he was logging it.

In Anthony's case he has crappy fuel around him and assume he is running the stock chip, is this within the allowable range of the ECU, I just don't know. (and I am as far from an expert as you could get).

Thanks for the PDF Alex, this is going to be very helpful for me. I am currently setting up my car to run on an aftermarket ECU (got the car started on it yesterday ) But setting up the knock sensors in the new ECU is going to take some time, so I am learning as much as possible about it as I can.

axl911

Eric,

Your data is nevertheless useful to me. Looking at my knock counts, I noticed a very specific pattern when the knock indicator goes positive. It only happens right after tip-in when the TPS is becoming constant. Which is why I am suspecting the knock is a part of the DME trying to maximize timing advance in closed loop. See graph.

If this is the case, then I can simply discount this as normal operation. In WOT or open loop mode, I can probably set my ZT2 alarm trigger as TPS>66 + knock = ALARM!!!!

I am also running a wevo engine mount and a lightweight flywheel which makes racket and noise like an old MB diesel.

trophy

You have some very interesting data there, it is interesting to note the knock happens when there is already a richening of the AFR. You can see an initial lean condition (very minor) just after tip-in as the boost is rising. The fuel adjustment (load) doesn't react as quickly as I would expect.

What is the scale on the X-axis?

Ed Hughes

Why do you have crappy gas in DFW where 93 is plentiful? Is the chip already modded?

axl911

It is a supercharger so boost comes up very quickly. The left X axis is for AFR, Boost (not to scale), and knock voltageX2. Right X axis is TPS.

Below is a little tidbit on Motronic 2.5 Operations:

"Knock sensor
The optimal ignition timing (at engine speeds greater than idle) for a given high compression engine is quite close to the point of onset of knock. However, running so close to the point of knock occurrence, means that knock will certainly occur on one or more cylinders at certain times during the engine operating cycle.

Since knock may occur at a different moment in each individual cylinder, Motronic 2.5 employs the Knock Control unit - KCU (in the ECU) to pinpoint the actual cylinder or cylinders that are knocking. The Knock Sensor is mounted on the engine block and consists of a piezoceramic measuring element that responds to engine noise oscillations. This signal is converted to a voltage signal by the Knock Sensor and returned to the KCU for evaluation and action. Tests have shown that the 20XE & C20XE engines have a knocking frequency in the 15kHz frequency band.

The KCU will analyse the noise from each individual cylinder and set a reference noise level for that cylinder based upon the average of the last 16 phases. If the noise level exceeds the reference level by a certain amount, the KCU identifies the
presence of engine knock.

Initially, timing will occur at its optimal ignition point. Once knock is identified, the Knock Control microprocessor retards the ignition timing for that cylinder or cylinders by 3 . Approximately 2 seconds after knocking ceases (20 to 120 knock- free combustion cycles), the timing is advanced in 0.75 increments until the reference timing value is achieved or knock occurs once more when the timing is retarded or This procedure continually occurs so that all cylinders will consistently run at their optimum timing.

If a fault exists in the Knock Control processor, Knock control sensor or wiring, an appropriate code will be logged in the self-diagnostic unit and the ignition timing retarded by 10.5 by the LOS program."