canbaufo

Took a test drive in the Z with the dyno tuner (had to pick it up from out of town and let him do the tuning with me absent...no choice) ........and some KR kicked in on the very first WOT pull . I hit the recall and the scanner said there was 6 degrees of knock retard. I asked him about it and he said there was no knock retard during tuning....and that it must be "burst knock". He said there is nothing you can do about burst knock as it is programmed into the computer from the factory to suddenly retard timing if you are cruising along and hit it all of a sudden...but only when certain parameters exist. Well, I went on to drive it some more and noticed that the knock retard had thrown it into low octane mode......as the knock retard would very progressively take out timing relative to throttle position. This made me think it would be either true or false knock rather than this so called burst knock. If burst knock is a programmed in safety net then why would it throw itself into low octane mode afterward? I mentioned this to him and he reminded me that the gas in the tank was about three weeks old....so it could be making true knock because of that.
...What doesn't make sense about this theory is that I had rolled on the throttle somewhat gently in 2nd gear at about 2,500 RPM. The KR didn't kick in until about 4,500. So is there really something called burst knock that's programmed in the computer which is also unalterable? I am worried because the printouts he gave me have a dip in the graph at about 4,600 or so which suggests the same thing may have happened on the dyno pull. He said there was no knock according to his software and had a printout for that as well. However, maybe his software can't pick up the knock retard like my scanmaster can....maybe it works off something else.

Dr.Mudge

I thought that could be removed also, hmm.

On the dyno, you have to make assumptions based on real life situations. What is the dyno wheel weight versus the car weight, as your primary reason for making differences. If the wheel is 3,000 pounds, you should adjust accordingly, but perhaps adding a slight extra amount of fuel and removing a tad bit of timing (2º where knock starts would probably be a good beginner).

JSK333

I recently went through the same thing on my stock engined car. I was getting knock retard except the knock count wasn't going up (in other words, no real knock, it was preemptive retard).

Yes, burst knock is part of the programming, but it can be removed! I removed it and the car feels so much snappier. No mini-bogging when you punch it, as timing isn't being retarded any longer.

If you're using the stock PCM, you can modify or disable burst knock retard. I did with TunerCat.

canbaufo

What exactly do you mean when you say the knock count wasn't going up? You're either getting KR or you aren't so what do you mean? (that it wasn't increasing as you stood on it?....just a quick burst and then it went away?..kind of like false knock?) Do you happen to know if the burst knock can be removed with LT1 Edit? (that's what the dyno tuner uses)

canbaufo

Well, I could swear he did say you couldn't alter it. However, just got off the phone with him and he said you can but he chooses not to. He says it's a good safeguard to leave in there to compensate for those times that you're suddenly hitting it and the fuel regulator's trying to catch up (kind of like an FMU...although I have no FMU but still the stock regulator which increases FP at a 1:1 ratio). He said once I go through the gears I won't see anymore of the burst knock....it's just when you floor it from a roll in a given gear. He also said the burst knock is not recorded by his software even though it will show up on my Scanmaster. His software will only record true or false knock.
I will say this car pulls really hard at the low and mid RPM's and the gas mileage is fantastic (he even altered the closed loop tuning by raising the temperature to lessen integration.....had to run it at about 13:1 in cruise mode but it still gets awesome mileage because of the steadiness. The torque is great....even down at 2500 RPM this thing's making 347 RWTQ.

JSK333

As I mentioned, the retard I was getting is preemptive. So, you get timing retard, but there is no actual knock. My count wasn't going up, but there was still several degrees of retard. Others have had the same thing.

I've heard it described how your tuner described it. Since scanning after disabling it, I haven't had any real knock, so I'm thinking it's unnecessary for me (at the least). It might be good to keep with FI, though, for the reasons your tuner mentioned.

Project94Z

I am also curious about this "Burst Knock". I have a 94 M6 Z28 and I have logged some knock count increases that I don't quite understand. It seems that on a hard run(WOT) I will record a "Burst" of knock(count increase=75-150 counts) between shifts, while lifting on the throttle. This, in turn, will cause timing to retard from .5 to 11 degs. The "Burst" of knock that my Freescan is recording will all be seen at one sample time. Knock count will be at 3756 and next frame it will be at 3879 or so. I have Tunnercat and Freescan. All my timing is stock at this time.

Thanks for any information or help you can lend.

Kevin M.

JSK333

Kevin,

That is something separate from what is being discussed in this thread. I get that occasionally too, mostly with nitrous, off and on. The reason it increases from one sample to the next either has to do with your computer's speed or the PCM itself. The OBDI PCM isn't known to be super-fast, from what I've heard.

What you're getting sounds like false knock since you're getting it at shifts, but it could also be from sudden timing changes going from WOT MAP to a vacuum (closed throttle).

"Burst knock retard" is when the PCM preemptively retards timing due to large changes in airflow. Knock count won't go up with "burst knock retard."

Project94Z

Solomon,

Thank you for the quick reply. Do you know of any way to tune that down or out, to keep it from happening?

Kevin M.

JSK333

Yes, there was another thread on the subject in this same forum, which I started a few days before this one.

You can zero out the table called something like "burst knock retard, coolant vs. rpm" in TunerCat.

Solomon

canbaufo

Good....I think I'd rather have it zeroed out......that way I won't assume "oh, it's just burst knock" when I see a quick spike of knock on the scanner and will know it's either true or false knock. Do you see my point? I know it's a safeguard but it can be misleading when reading with a Scanmaster via real time viewing. I'll try to find someone at the track who has LT1 Edit and cable and get them to let me use it to zero it out....or I may wind up getting LT1 Edit myself and just running a long as cable from my upstairs PC (or just take the PC downstairs to the garage). Can't you get everything you need for ~ $200.00?

JSK333

I highly suggest you get TunerCat for your own tuning needs. I don't know of anything that LT1E can do that it can't, plus it has nice graphing features and nice tech support/CS.

Plus, it's only $90 total, and you can use it on as many OBDI 94/95 cars as you like!

At the least, you could disable it and see if you get any real knock where it used to be taken out preemptively--if not, leave it disabled!