Return of a Tuning Tale. Chasing classic knock

[XfireZ51]

So as some of u know, I ended up discovering a few issues with my motor including oil seepage into cylinders and defective injectors. With the better weather, I have been able to get back out there to now datalog th car w the changes and fixes I did including new FIC injectors, so its back to tuning. However, I am still recording knock altho its not exactly like previous. Before I would seem to get knock almost on a random basis and at a steady cruise
and with little to no change in operating parameters. I now believe that was due to oil seepage causing the detonation. Contributing to that was one particular injector whose aerator had deteriorated and was basically
streaming fuel into the cylinder. That kind of knock seems to have been eliminated.
I have attached some snippets of my logs where the knock continues to occur but inspecting the plugs doesn't show sign of any detonation (I have attached some pics of two plugs, one from each bank). Once I started to log, it was clear that the previous tune had been very rich contributing to why the right bank plugs were black. Oil also contributed to this. I believe what had been occurring is that the left side was signaling LEAN and so it was forcing the right side to make up for it by richening the overall mixture. With the injectors now replaced I could go ahead and re-balance the VE table. I took out quite a bit of fuel. Of course since all other fueling is dependent or based on the VE, I suspect that now the AE needs to be tweaked and that may be the cause of the knock. I can induce knock by simply punching the throttle and I have a couple of examples of that. Also show a screenshot form TPRT w a before and after comparison w current bin v starting point and the amount of fuel removed. In fact, as I look at it, the area I am recording knock appears to be the same region of the VE where the most fuel was removed.
An added piece of information. lLatter C4 Corvettes w ZF6 trans came w dual mass FW due to the square cut of the trans gears and heavy duty nature of the trans, especially Black label ZFs. A popular mod is to replace w a SM Fidanza. At idle the trans rattles depending on state of tune.

[XfireZ51]

Putting this extra image due to lack of space up above, but this shows that the most fuel reduced from the initial bin appears to be in the same region of the VE table as where the knock occurs. That leads me to suspect AE even more.
I am sort of talking out of both sides of my mouth. In one instance, at least a part of the evidence suggests I am dealing w false knock. On the other hand I am discussing adding AE fuel because of real knock. Question is which is it?

[Hib Halverson]

I have zero experience calibrating a 1G LT5, however, I have done cal with many different 96-up GM cars. While the method one uses to calibrate a pre-96 ECM differs, the same principles apply.

Some comments and questions.

1) Are you using a wideband O2S to gain information as to lambda or AFR?
2) In a 1G LT5 cal, is there a burst knock table?

Oil ingestion can indeed cause detonation.

It's interesting that most of your KR issues are coming at part throttle.

If you've backed off the AE, that could cause knock at tip-in.

It's very difficult to see detonation on plugs even with WOT "plug runs". I would think to see evidence of part throttle detonation on the plugs would be virtually impossible.

All C4s with the ZF S6-40 had dual mass wheels. Also, the gears in a ZF were never "square cut". All ZFs had helical gears but the early transmissions had a lower helix angle.

[XfireZ51]

Hib,

Thanks for ur input and perspective. Much appreciated. My exoerience has been w OBD1 and principally w Speed Density, not so much MAF.

First to answer ur questions,

1. I do have a WB O2 permanently installed in the RH header collector. Its a
Zeitronix ZT-2. Been using it since I had my 84. However, since I tune part
throttle in Closed Loop, I use the data from the NB O2s and the BLMs.
Tapping into the ALDL data, I use ALDLDroid app for datalogging and
TunerPro RT in combination w a Moates Ostrich 2 for calibration updating
and prom emulation.

2. No there is not any “burst knock” table in the LT-5 calibration as I understand
there is in the LS cals.

I currently believe that what I may have here is a combination of too much spark in that area of the SA table and also not enough AE pumpshot for tip-in.
In comparing my current calibration w a stock 92 cal, it seems as I may be a bit too aggressive w SA. In addition, as I stated previously, the most recent tuning sessions have had me take out significant amounts of fuel in the corresponding area of the VE table, consequently affecting the amount of AE for that RPM/MAP
region.
So my next cal will have a marked reduction in SA approaching more what had been used in the stock calibrations. If the knock decreases or goes away, then I’ll know I have real knock. If not, then I may begin to suspect trans and/or FW noise instead with corroboration from the spark plugs.
As we know, these motors do use oil, but the oil ingestion I had previously has been mitigated by redoing the IH gaskets and better sealing of the cylinder head crankcase vents. The detonation is not random as it seemed to be previously.

I have seen evidence of detonation in reading plugs when tiny particles of metal appear to have embedded themselves in the insulator tip of the plug.

BTW, yes the ZF were not “square cut”, I was using that description to characterize the how more aggressively the ZF black label gears were cut compared to the latter blue label gears. As u said, the black label used a lower helix angle.

[Hib Halverson]

Ok, so much for my wondering if LT5 cal have a burst knock table.

With later model stuff, I can' tell you how many times I've seen people, not knowing about how burst knock works, assuming they have trouble with knock.

My guess is you are not seeing evidence of detonation on the plugs because you're dealing with knock at light load. Detonation under heavy load, may pepper the plug end with those little flecks of aluminum because that's the piston starting to "burn" which may start happening under heavy detonation. Unless your part throttle detonation is massive and beyond the ability of EST to stop with knock retard, I doubt you will see aluminum flecks.

As you suggest, detonation at light load can be caused by by oil ingestion. I've seen that myself on an engine which had very high oil consumption. Obviously, it happens because oil is very low octane, thus, only a small amount of oil vapor present will put the engine in detonation.

I think your idea of making the spark table less aggressive and, maybe, bumping up the acceleration enrichment is a good place to start.

As for the ZF, somewhere around here I have the helix angles for both styles of transmissions, but I can't find the info.

When I had Barney, I had a standard flywheel installed. I never had trouble with any KR due to the lack of a dual-massl.

[XfireZ51]

Thanks for the comments Hib. I did a compare between the stock cal and the current SA tables. The knock has been occurring pretty much in the area of where SA appears to be significantly higher than stock. So I have made the mods to the SA table, and hope to take her out today or tomorrow to do some datalogging. I’ll post up what I find.
When u say “standard FW” was it steel or Aluminum?

[XfireZ51]

I did a recent datalog showing the effects of scaling back the timing in the area of the SA tables that was experiencing knock retard. Dropping the timing made a pretty significant difference in the KR recorded which would confirm that knock was, in fact, present. The knock that would occur at steady cruise is gone which also would suggest that the oil infiltration into the cylinders is also gone. You will see that the are a total of 3 Slow knock counts. Some of that occurred w Port Throttle Closed and I have made some additional reduction in SA for that table. The remaining knock, for the most part, was "induced" by blipping the throttle at cruise speeds. My next step is to bump up some Acceleration Enrichment(AE) and see if that addresses the remaining incidents of knock.

Unfortunately, I can't upload the datalog due to file size constraints. Other sites allow at least 1MB uploads of .txt and .csv files.

[XfireZ51]

Did some additional logging yesterday. Any knock I am getting is almost exclusively coming at strictly 1900-2000rpm and in the 55-70kPa range. I have basically reverted back to stock timing at this point in that area.
Getting burst knock at that rpm but at 90-100kPa or basically WOT, however, the timing there is again stock, so I am increasing AE as a test for that.
The burst knock is occurring when I am jabbing the throttle at highway cruise speeds. Really wondering if this is not a function of the on/off transition in the drivetrain.

[XfireZ51]

So took car out again today w cal that bumped AE by 10% along w small changes to SA in affected areas. Pretty much eliminated steady cruise KC. And frankly, I think the motor likes the additional pumpshot. Throttle response appears better by SOTP. I will probably bump AE again particularly where I could still induce some burst knock altho it was more difficult to do so than before.
Would love to get this thing on the dyno finally for some WOT tuning.

[XfireZ51]

Another datalog today. Primarily, I’m looking for KR at either steady highway cruise or with sudden accelerator movements. I bumped AE again mainly in area of 40-60% increase in MAP kPa. That seems to have worked. No KC at steady cruise, and 1-2 KC when jabbing the accelerator. The added AE seems to also have benefits in takeoff from standing start and responsiveness to accelerator inputs even very slight ones. It feels as if u have a 1:1 correlation between movement of ur right foot and and how the motor responds and moves forward.
Getting close. Feels good. Need to check oil usage.