Hello all,

I have a 99FRC with a Futral F-15 cam (236,239). I have been tuning with HP tuners for the past two weeks and have a question about knock retard. I am getting anything up to 7 degrees of KR when leaving in first gear, but is normally 4 or less. Not leaving hard, just a regular stop sign to stop sign leave. The knock normally comes in at 1000rpms, .32g/cyl and then slowly falls off through first gear and is totally gone afer I shift into second. My fuel trims are good and my afr reads close to 14.63. I have tried decreasing the timing off idle with no luck. TQ management is eliminated and I have decreased burst knock in the lower rpms, but did not try setting it to zero.

One possibility is that the tune is not perfect, causing the leave in first to be a little jerky which causes false knock. I can be very smooth and still get a few degrees, but if I am not smooth it does seem to increase the KR. IAT does not seem to be a player as it will happen at 80 or 100 degrees. I am at a spot right now where I am not sure if I can eliminate it - is it normal for a 6spd car with a cam? I know its not like having KR at WOT when it matters, but I would rather that table be zero. Am I just pulling hairs here, or is it something I really need to figure out?

I have another question regarding a normal problem. My idle dips hard on a hot start. It will shut off or come very close to it for the first 15 seconds or so. I have researched the topic and tried many different things: set the initial adder vs ect to 0 from 104*-on, tried to just decrease the stock values, adjusted the park position airflow in the higher ect, and other small changes but none seemed to help at all. My idle is set at 800rpm which may sound a little low, but the thing idles perfect at any time other than hot start and sits right at 14.63afr.

Attatched is a copy of my tune if anyone would like to take a look. Thanks for any help!

Gabe

 

Burst knock is not knock retard, it's KR's opposite number if
you will. BK tries to predict knock and squelch it beforehand;
KR reacts to sensed knock. If you have a timing table & fuel
map that makes for tip-in or high airflow-rate-of-change ping
(such as might be found with a cam that makes a lot of "front
slope" on the VE table) then burst knock may be a good way
to cover it. Or, a way to see your timing stolen unnecessarily
(like on older trucks w/ stock tune, a cam, and gearing that
lets RPM run up fast, traversing said slope and leaving the MAF
airflow (steady MAP but fast changing airflow) and Dynamic
Airflow (VE table time-filtering) way behind real air, so lean
fueling and a lower than real Dynamic Cylinder Air number to
index higher than appropriate spark advance.

The most obvious answer would be to pull out a little low-
top mid-throttle timing (anywhere you are stoich).

You may also want to tighten up the KR response, halve the
attack rate and double the decay rate for starters so you
don't get the full pimp-slap every time it whispers, and goes
away quicker. This will make clearer what events are really
going on, and dog you less.

 

Thanks for the response! I will try tightening up the KR like you said and pull the timing at stoich down a little more and just see what happens. From what I understand about BK, if my KR is halved and set to go away quick and I still see the same KR I am seeing now, then the BK is what is causing it? The computer is expected knock and preventing it due to a slow reacting MAF/dynamic airflow?

Again, thanks for the help, I want to learn as much about this tuning process as I can. By the way, I see you are located in Central Florida - what part? I live in Cape Canaveral, go to school at UCF.

Gabe

 

Lowering the attack rate will give you less retard per "blip"
so you will get less if it's just a transient thing, or see it ratchet
up in smaller increments if sustained. The "hit hard and hang out"
stock setup masks the real situation, which is fine for consumers
who don't know or want to know nuthin'.

There is a separate scanner PID for burst knock, you probably
want to log both (along with other things like IAT and maybe
ECT spark terms, since it's toasty warm out).

 

After lowering the attack rate and upping the decay I drove the car through a series of stop signs where the KR would kick in at every stop and start in the past. This time I only had it 1/4 of the time and all were at 2* except for one which peaked at 3*. I am now going to pull a little more timing out of my table and see what happens.

 

I pulled 3 degrees of timing out of my table, mostly where the KR was coming in and blended it into the other areas. Took it for a drive and I am still getting 2* in first gear. I had even richened up the 800,1200 VE cells a tad and still saw the KR. When is it time to rule this out as false knock or just accept the fact that it happens? Has anyone else ran into a similar problem when trying to get the tune right with a good sized cam and 6 speed? Have a good one,

Gabe