KR explained

[Lex]

I have a lot of questions regarding KR and I wanted to clarify things a little about several nuances of KR that are NOT caused by detonation and the timing curve in the map.

1. Spool up KR. Here you will see a bit of KR (anything under 1.0 I just take as a "we've reached the efficient point" sign). This is common and not to worry you if it dies down like it does here and does not exceed 2.0. Remember the ECU drops KR in steps over a certain period of time and you can see this here and in all logs. If the KR is dropping it means no more knock is detected and the ECU is returning the timing to the base table. Why in this log? Look at your BATs - they are higher than in other logs.



2. High RPM KR that is a result of mechanical noise/shifting. Again the same log you will see that over 6K RPM there is a 0.7-1.0 or so of KR creeping in. This is a sign of mechanical noise but at 0.7 it's not something to really worry about. Then take a look at the 2.1 value there before it goes to 0. That is where you let off the throttle and the motor moved in the engine bay causing again mechanical noise. This is very common - a fast spike just as you shift or right when you let go of the throttle. This is not knock - just the engine moving around in the engine bay - don't worry about this. You can decrease the sensitivity of the sensor in the high RPM region. However if it is very high KR (2-3+), you're either indeed detonating or have a VERY noisy engine (see comment below)



If you see consistent high KR (5+ during WOT runs) and it is not due to timing or during shifting this is caused by other mechanical parts. Anything from a timing chain, to injector seals, to a bent rod. So keep an eye and diagnose this instead of trying to tune around it. Below is that turned out to be KR caused by a bent rod. As you can see it ramps right up to the max 5.95 and sits there regardless of timing (which drops into negative numbers).




3. Cold engine KR. When the car is not fully warmed up (even if the temperature gauge tells you it's fine) you may experience more KR than usual going up in the RPM range or under boost. This is because the engine internals have not reached operating temperature and expansion and are just noisier. Rule of thumb is to drive the car for at least 15 minutes before doing full WOT runs ... or to get an oil temperature gauge. Either way, if the car is cold, it's best to let it warm anyways before really getting on it so this KR serves as a friendly reminder.

ADDED March 10 2013


Part throttle knock - some insight

I have recently swapped out the ECU in my car for the latest part from Mazda (It's a gen1 2008.5). This is a different part number from what came in the car and it supersedes all other ECU part numbers for gen1s (there are many). The interesting aspect is that the part throttle and warm-up KR have significantly decreased or completely disappeared with no other changes to the car. Before readings in the 5-6+ KR range were normal as the car warmed up or on the first run of the day as well as at part throttle. Now they are either at 1* KR or below. No hardware changes, no tuning changes, no weather changes, just an ECU swap.

Now how does this play into the whole KR bit? While we have access to some of the knock sensor tuning tables via ATR and VersaTuner, we don't have access to the filtering algorithm (in the ECU firmware) or hardware. Remember that the knock sensor is a microphone and the ECU filters that signal to interpret knock. Mazda may have updated the hardware or algorithms responsible for this. This is further supported by the fact that the newer cars (gen2) don't suffer from this "part throttle knock" syndrome nearly as much as the gen1s.

What does this mean? Well it means that the algorithm was perhaps overly sensitive picking up "false knock" initially and not just scaring enthusiasts but losing some efficiency at part throttle since timing was lowered. This can also put to rest some of the fears that people (mainly gen1 owners) have when they see high part throttle KR readings.