Weird spark knock during shifting

[91chevZ71]

I've been getting some counts around 28-3200 rpm 75-85 Kpa, but I think it may be something mechanical. I've reduced those areas by about 4 degrees now and it will knock even more now in the same areas. Nothing audible. I noticed today that the counts always happen when the tranny shifts. The trans is definitely on its last legs, but could it cause some false knock? I compared my total SA in those areas to my earlier dyno run datalog total SA and it is 9-10 deg LESS with knocks, whereas the dyno runs had no knocks with more SA. No shifts on the dyno, though. COuld there be a correlation?

[91chevZ71]

well, it's not the tranny. I left it in "1" and took it upto 5000 and it only knocked in the 2800 and 3200 RPM windows at 75 MAP. WTF

[1500chevy5.7l]

i have some of the same problem to..same rpm to 2800-3500 rpm and same 70+ map area.....not sure what it is

[YenkoST]

Lack of fuel will cause spark knock. Check the air-fuel ratio in that cell and we shall proceed.

[91chevZ71]

AFR is 12.3-12.5 as per PE AFR commanded.

[YenkoST]

Well commanded and done is different....you have a wideband to check it....if you checked it then its another problem and we'll move on.

Oh, one more thing...its not still in closed loop is it....b/c your BLM cell boundary might stop at 75 kpa....just another thought I had.

[91chevZ71]

sorry. have Zeitronix ZT-2

[91chevZ71]

definitely not in closed loop. I'm in PE by 2000 RPM, and BLM before entry is around 120

[YenkoST]

How much throttle %?

[91chevZ71]

about 90, prolly more like 80

[discostu]

Does it do the same thing at the same rpm in 2nd or 3rd gear?

Also, remember that it takes time for knock to start (not much time, but time nonetheless) so maybe look in your 2400-2800 rpm areas, you may be "developing" a knock condition in those cells and having the knock appear in the 2800-3200 areas.

[91chevZ71]

yes it does happen in other gears.
I'll post my spark data in a sec
http://i184.photobucket.com/albums/x246/bmd2_colo/KNOCKWTF.jpg

[YenkoST]

Ok, you should definately be in PE then....I was thinking if it was like 40 or 50% then it could be AE or a VE setting. Hmmmm. And it only has knock when timing was decreased right from the dyno tune? If that's the case, load up the dyno session tune and go for a datalog and see what you got.

[91chevZ71]

yeah. just looked at my datalog from the dyno, max SA was 34 at 5700 rpm. no knocks

[YenkoST]

Well, what about the 2800-3200 area cell...what was it? B/c this one is 24*.

[91chevZ71]

plus PE SA is about 27. which shouldn't be knocking

[YenkoST]

well, go back to that tune and see what happens....do some logs on it....might be false knock or something....shouldn't be anything mechanical unless the valves are not set right...

[91chevZ71]

mauybe I should recheck all the rocker arms, one might have come loose since I put rollers on

[YenkoST]

could have

[Fast305]

Look at the MAP AE while the transmission is making its shift. Increase the Delta MAP AE in the area that is being used on the log of the upshift. It should be the 5-15 KPA range, toward the bottem of the table. Increase it 10-15% and see if the knock does not go away. When the transmissions shifts at part-throttle, it creates a sudden surge in Manifold Pressure and causes the fuel to partially drop out of suspension in the manifold and cling to the manifold walls. You need an extra shot of MAP AE to help cover this as the throttle is at a steady state.

[91chevZ71]

Wow. Interesting. Now that you mention that, I decreased MAP AE a bit and I wonder if you're right. no surprise

Thanks Fast and Yenko for the help. I'll try this out tomorrow morn.

How did you learn that???

[Fast305]

Wow. Interesting. Now that you mention that, I decreased MAP AE a bit and I wonder if you're right. no surprise

Thanks Fast and Yenko for the help.

How did you learn that???

The "School of Hard Knocks".

[91chevZ71]

nice. good one

[discostu]

Fast, what kind of ratios are you using for TPS AE and MAP AE? I've heard of (and seen) most tunes using around 66%/33% TPS/MAP or somewhere around there... Anything between 50/50 and 80/20 I suppose.
Obviously there's not going to be a "golden ratio" as such, but I'm just curious how your tunes have ended up.

[Fast305]

Mine is about 60/40. 60% to the MAP and 40% to the TPS

[91chevZ71]

mine is 60% TPS, 40% MAP

[buick_93]

I've been having having the same problem in the 2400-3200 RPM 90 MAP area with knocks and cleaned up most buy not all with new header gaskets. Then I switched from 87 octane to 92 octane and it didn't clean up the 9 knock counts I was getting, so I'm betting that I have some false knock somewhere.

I've also been getting the knock counts in the 3600 RPM area on the upshift, and I talked to RBob about it and he says it could be noise from the transmission when it shifts gears.

[Fast305]

I've also been getting the knock counts in the 3600 RPM area on the upshift, and I talked to RBob about it and he says it could be noise from the transmission when it shifts gears.

Check for a bad transmission mount or worn U-joints. Both can cause the knock sensor to be triggered.

[91chevZ71]

U-joints are about 2 weeks old, trans mount is very old. If it was something like a valve out or something, wouldn't it be knocking all the time? It might be some carbon buildup, but my plugs have textbook signs of normal wear. I seafoamed it the other day, no smoke. I seriously doubt there is a hotspot somewhere, but I can't be sure. The only thing I know is that there is a little dip in my SA table right around 2800-3200 rpm and 70-80 MAP. What I don't get is when I first started tuning the motor, I had a butt-load of SA in an it wasn't knocking at all. Granted, I was running real rich so the extra fuel was probably helping out. I've compared my SA to yours (Fast) with a table you posted over at Thirdgen and I'm less all around. I have leaned out the VE a bunch and have been refining it for a while, and the hotter weather does not help. Ah hell, it runs pretty well.

[buick_93]

It might be some carbon buildup, but my plugs have textbook signs of normal wear. I seafoamed it the other day, no smoke. I seriously doubt there is a hotspot somewhere, but I can't be sure.

I seafoamed my car a month ago thinking the same thing, and it did not change anything either.

91chevZ71 what octane fuel are u running?

[91chevZ71]

91 all the time

[buick_93]

91chevZ71 I've been researching over on thirdgen during my lunch breaks and it looks like changing the burst knock settings in the chip can cure the knocks between shifts. Something we'll have to dig into.

[91chevZ71]

Definitely. I'm gonna ask Rbob about it, see what he thinks. Burst knock, huh? gonna read up on it