Camaro ChriSS

I recently added a h/c setup. AFR 205s 66cc unmilled with a 224/224 cam. I've been playing with WOT tuning and I can't seem to figure out some Knock Retard I am finding that has started up.

My tuning efforts aren't getting rid of it (unless I haven't been extensive enough) so I'd like to know if anyone has seen similar patterns to mine before (and solved it - that would give me hope).

First, it only occurs in 3rd, right when it shifts into 3rd - starts at the bottom, at 4500 rpm, of 3rd and slowly falls. It is about 3.6-4.0 to start, then fades by 5600. I would expect this due to the higher load of resistance in this gear. Never in 2nd or 1st (A4).

Second, its not always there. I can make one run and KR shows right at 4500 rpm. But then I make 5 runs after that with not a trace. Can KR just come and go like that? I've never seen that myself, but have others?

Third, it is strongest in the first run, usually. The first run I will make into third will show KR, but subsequent runs likely won't if I don't turn the car off. But this is not always true. Sometimes the first run is ok and another run shows kr. This may be a coincidence. ?

Four, I initially started by raising timing to see the effects from stock of 23 to about 27 (in the 4400 4800 rows). There I got KR on the odd run, but most were knock free. So I figured it was too much timing. Backed if off in stages down to 23 (stock ) again, and each time there was no change. KR would be about 3.6-4.0 at start, then fade - and would only appear in the odd run. So my timing adjustments haven't had much impact. No wideband #'s, but my O2's are consistently 925-950, and ST and LT are largely negative (LTs about 0 to -2.0, but occassionally +2.0).

Would a bad Knock sensor be intermitent like that? I would expect that to be consistent at 4.0 or so, and not drop or dissappear.
Or, is this a typical pattern (comes and goes)?
Could it be that I have to have less timing than the stock table at peak torque? I wouldn't have guessed this.

I haven't tried scaling up my PE table yet. I may do this if no one has any suggestions.

Any help would be great.

Camaro ChriSS

Did I make my post too long? I'm hoping someone has seen this pattern.

To sum up:

1. KR appears irregularly - one out of 5 runs for example.
2. Only in 3rd gear - starts at shift (which is peak tq at 4500 rpm)
3. Fades by 5600 rpm.
4. No different pattern whether I use 23 through 26 degrees timing there (same level of KR at 3.6-4.0).
5. Never in 1st or 2nd.
6. Running stock PE tables still and ATap doesn't suggest a lean condition.

Its like looking for a ghost for me so far.

rawlitogut

I have the some problems,but only have less then 1 degree. Iam alos running 27*

Camaro ChriSS

Are you running 27 degrees at 4400 or so, or just higher rpms? What have you attempted to eliminate it?

Camaro ChriSS

To keep anyone who's watching up to date:

I increased fuel by 2% through PE vs RPM in the 4400-5200 rpm range to see if it would help, but no change. O2s are .930-.950 now. Still intermitent KR in the exact pattern. I will attempt to remove timing below stock to see if it will help.

Currently my fuel is:
4000 4400 4800 5200 5600
1.2403 1.2650 1.2650 1.2650 1.2403

Ignition (HO) in the WOT range is:
3600 4000 4400 4800 5200 5600 6000
29 26 24 23 26 29 30

I notice no engine vibrations, banging, etc... in 3rd. So I can't think of any external issues from my recent heads and cam install.

One possibility is the jump in timing I have at the shift point - 6400 rpm is 30, and 4400 is 23 degrees - after the shift, could the jump in timing be an issue? I would not think so though because that is a small jump relative to what TM causes (30 - ~0 - 23)?

sleeperstyle

iTrader: (4)

high o2's imho, . i get that "sometimes knock" too- i tried EVERYTHING and got soo frustrated with it i just don't give a **** anymore. 4*or less of kr for me sometimes, oh well...

we should start a "phantom knock retard" club.

rawlitogut

I have the predator so only in high RPM

Camaro ChriSS

I agree with the phantom KR club....

I added more fuel (between 2-4% between 4000-5600 rpm) and decreased timing at WOT to exactly stock numbers again (even at high rpms where I never saw it before).

I made 7 runs, and on the first 6 runs, I didn't get a sign of KR. Everything looked great, but then on my 7th run, the KR appeared again. But this time it started in 2nd gear and contniued through 3rd gear. Worse (3.5-4.0) at 4K rpm, and dropping to 2 degrees by 5K+. Repeated this pattern in 3rd gear. Odd because it never appeared in 2nd gear before.

And I can't figure out why it suddenly appeared again on the 7th run. I was about to conclude that the problem was solved... seems not. What could make it come and go like that?

sleeperstyle

iTrader: (4)

no more fuel for you! get that thing on a wideband before you wash the rings! j/k man but honestly you DON"T need more fuel. i'd look elsewhere like stupid **** ie. vibrations from exhaust or whatever.

Camaro ChriSS

I think I've covered the fuel issue and timing issues relatively well. But, even so, the O2 sensors are pretty bad at gaging AFR, and I've seen h/c cars hit the wideband and come up with a 14.0 AFR at WOT. And, with the small 26 # inj. I got, there is still the possibility of lack of fuel. SO I still could be lean, despite the O2s.

I can't find anything mechanical thats at fault. And if there was, I think it would appear more regularly on my runs. I know I've had a banging y-pipe before, and although I could definitely feel that when I had it, it never showed up as knock. And I don't have the banging pipe now, thats for sure.

I guess I'll just have to hit the dyno. I will update this post when I get more findings.

No other gurus got any suggestions?