Silverado 5.3 Ghost knock retard HELP

[bigdaddy9185]

I have a 2011silverado 5.3 flex fuel and my friend and I have attempted to get rid of knock , that can not be heard, good gas exxon premium
have reduced the sensitivity of knock sensors and eliminated burst knock retard, and have very little advance in it at all , when I first started tuning this truck I was able to add timing but as time has progressed and I have moved to other problems this seems to reappear , I have taken into accout the temp here in texas and done my changes and tuning in the night to maintain 80 degree temps so any possible places and things to check out to verify that I'm not crazy is a blessing , thanks in advance.

[IARLLC]

I just spent several days with a 2007 Tahoe 5.3 flex fuel with the same continuous KR issue (idle, cruise, accelerating). From the factory these experience quite a bit of KR. I think they are designed that way to get maximum fuel economy and burn the gas as completely as possible. But this Tahoe was taking away so much timing to recover that he was actually losing a lot more performance than need be.

Details: Shaved heads, gutted cats, well over 100 degree weather. very low quality gas with enough alcohol to really get the Flex system enriching commanded AFR.
A few things really helped:
1. Text book KR treatment would suggest taking as much timing away as the logs show. I did not do that. I spent a lot of time watching the logs looking at the exact points that the knock initiated the super-heating of the cylinders. Then I retarded primarily at those points and just a bit beyond them. This process took a long time but in the long run I ended up retarding about half of what the logs initially would have suggested.
2. Because I did have to retard the High Octane Timing Table quite a bit it became really important to also retard the Low Octane Timing Table (high was lower than low I really hesitated to retard the timing much but the truth is it did not need that much timing for higher compression and alcohol. I did not remove so much that it never gets KR...just enough so that it no longer throws the vehicle into a kind of KR dance that perpetuates itself. It actually experiences quite a bit more timing than it did before.
3. I don't understand exactly how the system uses Max Torque Timing but it seemed to help quite a bit that I reduced the most sensitive areas 3 degrees.
4. Biggest difference was tuning the VVE. No cats, weird gas, higher compression... way off.
5. Not totally sure but there may have been a metal-to-metal squeak from one of the exhaust joints showing up as knock at an idle.... even at very low timing. One of my guys trimmed the clamps just a few thousandths to get the joint to quiet down.

End result is a huge smile on the client's face.

[bigdaddy9185]

Here is a copy of my tune look at it tell me what you think , again thankyou in advance for any help .

[IARLLC]

I compared your tune to the one I just finished on the 07 Tahoe. I am really curious to see what situations are giving you KR. Please send a log.

For 09 the factory advanced the cam in the freeway-medium load region which will add a good bit of compression to the region. Also noticed that SD is turned off over 2200. Maybe it is for the best but I would just be curious to see your log to see what affects this is having. Also PE of 1.13 across the board would have leaned out our client's Tahoe really bad. It was a little over 1.3 by 4800RPM. Did you use MAF cal to enrich your higher RPM?

I have heard there are several ways to refine these and I am no expert. I am curious what the experts have to say... but in the mean time if I get to look at a log we might find some answers

[bigdaddy9185]

Justins Full Tune Silverado 11-25-16 low fuel pressure timing increase 2deg.hptI tuned the maf and vve both, but found that the shell gasoline was the problem had upwards of 20 percent alcohol content and took a sample from tank and allowed it to sit for a week and acutually saw water separation in the fuel . no longer use shell products and now use EXXON premium exclusivly will post a tune showing the differance of how much timing was able to be added
note I am still adding timing and then picking away at knock to maximize timing map then run the low octane at 4 degrees lower than high octane , also DOD causes lots of knock issues I was able to solve some of those and then one soliniod failed and I turned it off actually got better fuel mileage after turning it off by 2 mpg , also increased fuel pressure over stock slightly makes a differance but do not go above 48 psi will cause injectors to leak fuel and fill crankcase with fuel reducing pressure eliminates the fuel leak problem

[GHuggins]

Sounds like the ethanol may have actually damaged your injectors - they should hold high pressure without leaking a drop.......

[bigdaddy9185]

Sounds like the ethanol may have actually damaged your injectors - they should hold high pressure without leaking a drop.......

what do u think about the tune , you replied to my post earlier on the variable cam just curious on your thoughts any place you see for improvement

[IARLLC]

First, what I wrote above about GM advancing the cam in medium load areas was WRONG. Sorry! Thanks to some of your questions a few months back I dug into the VVT stuff much more. What i was referring to is actually major cam retard to DECREASE cranking losses on the highway (slightly improving mileage and getting rid of EGR.

On that note...because you brought it up and I looked at it a lot more...I was able to really increase driveability on 2500 6.0 set-ups. Like yours they don't start retarding the cam until 4k and 0 degrees does not represent 0 but actually represents a lot of advance...and they are noticably weak up until the sudden surge in power at 4k!!! So I studied how GM runs their Escalade and Denali 6.2s. They start to retard the cam much earlier....and they have a lot smoother power down low. Anyway, since then a few of my heavier 6.0 clients are pretty happy with the improvements from running a cam strategy more similar to the light duty 6.2 SUV/trucks. There is an obvious improvement in power/behavior in the light/medium throttle areas below 4k. It would be interesting to measure the actual improvements on a dyno. You can see examples of this cam strategy in any 1500 6.2 file from the repository.

[bigdaddy9185]

so download a 6'2 file and copy and [paste the maps for retart on cam ??? what section lable do i need to go to to find it

[IARLLC]

Yes. You can just open your file then to the compare file thing with a similar year 6.2. Engine>Airflow>Variable camshaft>Intake camshaft>Base angle> I blended all three tables (Low, Medium, and High) keeping the smooth blend from bottom to top but I reduced the major advance bump in the low/mid range to about 25% of what GM had.

In addition to this after LOTs of time looking at ignition profiles I decided to keep the tuned timing curve from the 6.0 and use the Engine>Spark>Advance>Variable Cam. GM advanced the ignition timing about 1.5 degrees for about 4 degrees of cam retard. In a separate window I kept a map of my cam advance "show differences". And based on these differences I increased or decreased timing at a rate of 1.5 degrees ignition advance for each 4 degrees of cam retard. Since the maps use the same axis it was pretty easy to just look at whether I increased or decreased cam timing and decrease or increase the ignition timing. For example the whole right side of the cam advance map will be retarded 3-4 more degrees (12). So the same exact points on the variable cam ignition advance map I increased timing 1.5 degrees, etc, etc.

It might take a bit of rework on the ignition curve after this depending on the gas quality and this and that...but this is what I did and I really liked the results. Enjoy!