Negative FLKC but IAM stays at 1

[Tectoniic]

I can find so many threads and general info about IAM dropping with no FLKC but none where the IAM stays at 1 even though FLKC has negative values.

I know it is hard to diagnose without a log but I have never been logging when it happens. Very sporadically I will get small FLKC values, usually -.29 or -.65, when I am in 6th gear with ~10% throttle and ~1500-2000 rpm. During this time the IAM will stay solid at 1 and nothing else seems to be off. The small negative value will usually continue to show up for the remainder of the drive when the above conditions happen until I shut the car off.

This happens very infrequently so I am not worried about but I would like to try and get it resolved or understand what is causing it. Any idea what could be causing this(possibly a glitch in the OFT or maybe just bad fuel?) or steps I could take to test?

[Kodename47]

It's pulling timing in response to the detected knock. This is common and tends to happen in high gears. The fact that the IAM is not dropping is because it's infrequent and the ECU determines that the IAM does not need to be reduced. I have seen quite a lot of knock correction and still have IAM of 1. The ECU will not always drop IAM.

You could try and take 0.7 degrees out of the timing in the affected area, however I tend to ignore FLKC above 4th gear at lower RPM unless it's pulling a ton of timing or is very consistent just because the loads on the engine at low RPM tend to make it do this.

Also remember that FLKC is learnt knock and the likelihood that the -0.3 values are actually timing being restored, and potentially some occurrences are the learnt knock and not pulling timing in direct response to detected knock but from previous events.

[steve99]

+1 on what @Kodename47 said.

The ecu uses some complex calculation to determine if it will drop iam on knock events

It appears to look at

Size of the knock event ie -0.7 or -1.5 or whatever is detected
Duration of the event ie is it shown as a spike in log or a bucket shape
The frequency of knock events ie a whole series in close sucession

How long ago did you get the last series of knock events

From observation you will need a substantial number of knock events in a short period of time to trigger an IAM drop if the events are less that -1.

As the size of the event increases say to -2 then IAM drop will occurr after much less events

Log the stock tune on your 91 fuel and observe all the knock and iam drops then think that heaps of people are driving round like that all the time blissfully unaware and their motors are still running NA, once you start adding boost it a different story

[Tectoniic]

Thanks @Kodename47 and @steve99!

Last time it happened was this morning on the way to work. It happens so infrequently that everytime I go driving with the purpose of trying to catch it it never happens. I figured it was pretty insignificant but couldn't hurt to ask.

As soon as it happens(of course while I'm not logging) I either back off the throttle or give it more throttle which gets it out of the "knock range" and it goes right back to 0

[Wayno]

Generalising a lot here, but the ecu won't drop iam until it sees around -2 flkc repeatedly, and more so in specific areas. Don't detune your timing just because you see low levels pulled.

[Kodename47]

Originally Posted by Wayno

Generalising a lot here, but the ecu won't drop iam until it sees around -2 flkc repeatedly, and more so in specific areas. Don't detune your timing just because you see low levels pulled.

IIRC it's any FLKC value over 50% of the Advance Timing table, if the table value is above zero.

[steve99]

Originally Posted by Kodename47

IIRC it's any FLKC value over 50% of the Advance Timing table, if the table value is above zero.

Is that the "Knock correction Advance Max A" table ?

If so I have seen IAM drop due to FLKC, with the FLKC value being less than 50% of the value in that table at the load/rpm where the FLKC was logged.

Recently been chasing some FLKC knock thats been dropping IAM , FLKC was less than -1.5 correction but IAM dropped and my entire Advance MAX A table was over 4.2

The other theory I heard was that if the value in the table was less than about 3 (or maybe 2.7) then this inhibits FBKC from droping IAM as Coarse correction is disabled. But FLKC is always active and always drops IAM if certian parameters are exceeded, what these are I have no idea.