mypoorLS1

iTrader: (4)

My car has always had it. From the time I put a small cam in the stock motor until now. I've changed a lot of things. When it was on the dyno I was thinking it would get straightened out but he couldn't get a proper fuel ratio due to needing a bigger fuel pump. I installed an aeromotive 340. I don't want to take it back to the dyno only to need something else. When it gets tuned this time I w ant it to be done. Any ideas?

outkast6991

iTrader: (34)

Is it burst knock? I assuming that what your referring to. I'm not an expert by any means but my understanding of it is that on any major change in throttle position or engine load the PCM pulls spark in anticipation of possible knock. There is a burst knock table in the PCM that deals with this

mypoorLS1

iTrader: (4)

That may be what it is. My PCM is a 98. Not sure if it had these tables but I will look. It only seems to knock when you are moving the throttle open. Seems to stop when you stop pushing the pedal down

salemetro

iTrader: (5)

Correct. However, it could be a number of things. The PCM will access the Primary VE tables during transitions as well... usually below 4000rpm. Above 4k, the PCM usually goes MAF only. It's possible that the VE table needs to be worked over, since it was running out of fuel the last time that it was on the dyno...causing all sorts of AFR issues. However, this is all just speculation as to what the issue really is. It sounds like you've got the fueling supply issue handled.....I'd just take it back to the tuner and get it finished. Just make sure that your injectors are the correct size for your mods/anticipated power level.

mypoorLS1

iTrader: (4)

I have 42 lb injectors. It should go on the dyno again within the month. I was just looking for other things that may cause it. I had this knock with my last combo as well but it was very mild. I also just moved and now have emissions to deal with so I may have to de mod a bit

soundengineer

iTrader: (16)

when on the dyno I change the tables for burst knock so that they cannot be triggered....
its a calculated value, and you arent doing WOT for throttle transitions

I do three things when I tune...

First, I put the car in SD by diabling the MAF... physically unplug it, make sure codes are set to MIL on First Error, and tune the VE table First

2nd, I re-enable the MAF, put teh dynamic airflow vale to 400 rpm(default stock is 4000 rom)
this makes it so that the MAF is 100% in control above 400 rpm, then I tune the MAF table


3rd, I set the MAF dynamic airflow value back to a reasonable value...it can be 4000 rpm, or even something lower... a big cam may only get 3000 rpm, a small cam or a stock cam can go much lower...stock cam can be set as low as a couple hundred above idle rpm

the trick is to pick a point where you want the MAF to be 100% in control... which needs to be a point where the airflow doesnt see any cam reversions.
obviously the more overlap, the higher the value needs to be.

the tune will blend MAF and VE below that dynamic airflow RPM, and go 100% MAF over that rpm value.
it will also go 100% MAF anytime it feels that you have reached a "steady state"... which is calculated from MAP and TPS variations...so basically shortly after you mash your foot at WOT, its going to be using the MAF 100%, but as soon as you let off, its going right back to the VE as soon as it goes below that dynamic airflow RPM..

its also the reason why some tuners cant figure out why the tune keeps jumping around on them on deceleration and very low MAP values

mypoorLS1

iTrader: (4)

That makes sense. I'll have him look into that. Thanks