Low RPM knock

[Bad Habit Z]

I have been searching through all of the threads about Knock issues but can't seem to come up with a good answer for this. I recently started logging on my 01 Z06 (stock except for blackwing intake) and at low rpm's when I give it a lot of gas I get some KR for a bit.

At first I thought it was burst knock then realized BK doesn't show up as KR. I also have a WOT pull about halfway through the scan that I get a fair amount of KR in. During that same pull the AFR cmnd steps down a few times as well, I'm not really sure what that's about either

If someone could just point me in the direction I need to go to get this fixed I would greatly appreciate it.

[WS6FirebirdTA00]

have you tuned the car with a wideband yet? Have you messed with the timing? If not get the fueling inline and if there is still knock there then pull some timing in the areas you get it.

[Bad Habit Z]

The timing table is still untouched but I have made a few adjustments to the VE table to get it where it needs to be.

Why does the AFR Cmnd step down like that on the WOT run?

[jimmyblue]

Your PE vs RPM may be "notchy" and not enrich
as much as you need at low RPM. Look at the
profile in the 2-D view and imagine this against
the RPM in time; look similar?

Presumably this car has a PE enrichment rate of
1.0 like any vehicle that doesn't need towing
fuel economy should?

The right answer may lie more in driving style,
avoid lugging the motor and shift into the power
band ahead of throttle.

[Bad Habit Z]

I scanned it again on the way home from work and the fuel trims look pretty good to me. It seems that if I give it too much gas quickly while cruising the KR starts and will not stop until I let off of the gas.

It even gets KR at higher rpms as well, if you look at the attached scan around frames 4900, 7100-7500, 8200, 8900 there are some examples of when the KR is showing up.

Should I load the stock low octane timing table and try to gradually bring the timing up where I can? I am just suprised that it has so much KR with the stock timing tables.

[WS6FirebirdTA00]

are you tuning WOT with a WB or just looking at fuel trims?

[Bad Habit Z]

Just going by the o2 readings until I can get my wideband. Isn't .900 and higher more rich right? .880 -.890 is where you want it to be at WOT right?

[WS6FirebirdTA00]

dont even attempt to go by that, my car was lean at 0.900, and my friends was rich at 0.890. Definately not consistent from car to car. If I had to make a guess, I would guess you were running on the lean side.

[Bad Habit Z]

So should I richen up my PE table or tune the VE table to run a little rich?

[WS6FirebirdTA00]

no, you shouldnt really do anything until you get a WB so you do it correctly. If you did want to just add fuel to see if it does anything then you need to add it to the MAF table or VE table depending on what mode you are in.

[Bad Habit Z]

I think I will pull 2 degrees of timing across the table and adjust the fueling to make it just a little more rich and see what happens.

thanks for the help

[5_Liter_Eater]

That could get rid of your knocking but you're really flying blind.

I used to think, "Hey, I'm ~900mV, that's good enough". Used to think I could get away with tuning via narrow band knowing I would always back it up with a wide band when I had time to hit the dyno (this was pre-supercharger BTW). Now that I have an on board WB and am tuning open loop I can see that it is truly impossible. Right now cruising at ~14.7:1 my O2's are in the 890's. There are other places in my log that 890's equate to ~13:1. When I am WOT they are 940-950 which is 11.5:1 on my car.

I hate to become one of those guys who pushes the need for a WB but it really is true.

[Dragman]

That could get rid of your knocking but you're really flying blind.
I hate to become one of those guys who pushes the need for a WB but it really is true.

I agree!

[Bad Habit Z]

Ok so I got a wideband and have been recording with it lately. I am still getting this knock though I have installed 42lb injectors and TSP longtubes since the first post I made.

I have tried pulling timing and adding fuel but neither of those seem to work. It seems like I am getting the KR anytime I just punch it real quick and even if I try to roll into the throttle some.

I'm not really sure what to do now.

[shimp]

I hate to waste space here, but after watching the first log you posted... I noticed that I get the same kind of KR in my truck. And it's tune is completely stock, VE, spark etc is untouched. I thought it was because I am running 87 octane and may need to back off a little timing where my engine gets loaded hard under normal driving. Like midrange rpm 2000-3000 with less than 50% TPS. I hardly ever get KR under WOT above 4000rpms... But I get it alot at lower rpms. I think my knock sensors are too sensitive. I have never heard an audible knock....

[Bad Habit Z]

I haven't heard any knocking ever from my car and I haven't changed much in the tune other than adjusting the VE table some. It did the same thing even with the stock tune in it also.

[Bad Habit Z]

Anyone?

[WS6FirebirdTA00]

if you give the car a lot of gas in low rpms it will knock if there is a lot of load.

[Bad Habit Z]

if you give the car a lot of gas in low rpms it will knock if there is a lot of load.

So every car does this?

[jimmyblue]

Your timing is in degrees but the real time at low RPM
is mighty long, for burn to get going. 30 degrees at
1000RPM being the same as 60 degrees advance at
2000 on a time basis, and the burn time actuals not
much different. Do you need that much spark lead?

By way of reference I had an old 10:1 CR Buick
motor that wanted zero degrees idle advance. Yeah.
Our tables have way more to begin with and that's
before you start messing.

At the low end there is so much opportunity for error
in the airflow side of things, you might just be over-
lean from that. PE enable RPM may keep you in an
unenriched mixture.

The right answer probably is "don't do that". An auto
will just keep you out of it, a M6 you have to either
make the motor happy by shifting smart, or make it
safe by removing unnecessary advance.