Turboed LQ4 - Knock Sensitivity

Hello. I would greatly appreciate some insight and experience. I have a 68 C10 w/ a stock internal LQ4 (minus Tooley double valve springs), solid motor mounts, rubber trans mount, 2002 Silverado ECU, GT45 Turbo, 4L80E w/ stock TC, 3.08 gears, and 295/55 MT tire, running 91 octane. I have read multiple forum posts on this site and others regarding knock sensitivity, but am still confused, so decided to make a forum post to see if others had already been through and had experience w/ my issue.

I recently got my truck running a couple months ago and have slowly but surely been tuning it. My VE was way rich to begin w/, so it took me a bit to get that dialed in. As of a couple weeks ago, I had it tuned to 5 psi w/ good results (power and data) and currently am at 8 psi. Everything w/ the tune has looked great, except for periodic Knock Retard when at WOT. This is NOT Burst Knock, as I have that disabled. In looking back at all of my logs, the knock has occurred all over the timing map, but of most recently has been occurring at around 3500 RPM, 4 lbs boost, at .91 g cyl airmass, wherein I am commanding 14 deg of timing, which I viewed as pretty conservative. I am not "hearing" any knock. I have only a downpipe and one exhaust pipe to deal w/ and it is secured well and not interfering w/ the frame. Today I tried to reduced timing by 5 deg in the area of the map that has recently shown issues, and I still saw Knock Retard (this was at 11 deg of timing at 3400 rpm and 4 lbs of boost). I also disabled the Tip In Knock by setting my min threshold to 10000 RPM, and again still saw knock. I have NOT changed any of the knock sensor setting except for the recover rate, wherin I multiplied the stock values by 3, and knock recovery is now much quicker. I do not have easy access to high ocatane fuel / race gas, but Im guessing that is probably my next test to try to determine if the knock is fake or not.

I visited w/ a friend who has turboed a 1/2 dozen or more LS engines very successfully, and he mentioned that he doesnt install Knock Sensors anymore, and that I would be chasing my tail if trying to utilize them, as he has experienced the same issues as I. I dont have access to E85, cant afford a dyno, and dont want to hurt the motor, so I initially was very intent on trying to utilize the knock sensor for tuning, when I get to a point of fine tuning the timing.

Sorry to ramble... just wanted to provide all the pertinent details. I would like to know if there are any others out there w/ a similar setup as mine, w/ a LQ4 w/ stock Knock Sensor sensitivity settings that went through similar issues as I? Given the information provided, do you feel it is fake knock? If it is fake knock, Im guessing Im either going to have to change the "Knock Sensor Level vs. RPM vs Cyl" table or the "Knock Sensor Global Gain vs RPM vs MAP" table. Does anyone have experience which table/s to change and by how much?

I appreciate your taking the time to read of my issue, and thank you in advance for any advice you could give.

THANKS
ANDY

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Originally Posted by AndyGrove

Hello. I would greatly appreciate some insight and experience. I have a 68 C10 w/ a stock internal LQ4 (minus Tooley double valve springs), solid motor mounts, rubber trans mount, 2002 Silverado ECU, GT45 Turbo, 4L80E w/ stock TC, 3.08 gears, and 295/55 MT tire, running 91 octane. I have read multiple forum posts on this site and others regarding knock sensitivity, but am still confused, so decided to make a forum post to see if others had already been through and had experience w/ my issue.

I recently got my truck running a couple months ago and have slowly but surely been tuning it. My VE was way rich to begin w/, so it took me a bit to get that dialed in. As of a couple weeks ago, I had it tuned to 5 psi w/ good results (power and data) and currently am at 8 psi. Everything w/ the tune has looked great, except for periodic Knock Retard when at WOT. This is NOT Burst Knock, as I have that disabled. In looking back at all of my logs, the knock has occurred all over the timing map, but of most recently has been occurring at around 3500 RPM, 4 lbs boost, at .91 g cyl airmass, wherein I am commanding 14 deg of timing, which I viewed as pretty conservative. I am not "hearing" any knock. I have only a downpipe and one exhaust pipe to deal w/ and it is secured well and not interfering w/ the frame. Today I tried to reduced timing by 5 deg in the area of the map that has recently shown issues, and I still saw Knock Retard (this was at 11 deg of timing at 3400 rpm and 4 lbs of boost). I also disabled the Tip In Knock by setting my min threshold to 10000 RPM, and again still saw knock. I have NOT changed any of the knock sensor setting except for the recover rate, wherin I multiplied the stock values by 3, and knock recovery is now much quicker. I do not have easy access to high ocatane fuel / race gas, but Im guessing that is probably my next test to try to determine if the knock is fake or not.

I visited w/ a friend who has turboed a 1/2 dozen or more LS engines very successfully, and he mentioned that he doesnt install Knock Sensors anymore, and that I would be chasing my tail if trying to utilize them, as he has experienced the same issues as I. I dont have access to E85, cant afford a dyno, and dont want to hurt the motor, so I initially was very intent on trying to utilize the knock sensor for tuning, when I get to a point of fine tuning the timing.

Sorry to ramble... just wanted to provide all the pertinent details. I would like to know if there are any others out there w/ a similar setup as mine, w/ a LQ4 w/ stock Knock Sensor sensitivity settings that went through similar issues as I? Given the information provided, do you feel it is fake knock? If it is fake knock, Im guessing Im either going to have to change the "Knock Sensor Level vs. RPM vs Cyl" table or the "Knock Sensor Global Gain vs RPM vs MAP" table. Does anyone have experience which table/s to change and by how much?

I appreciate your taking the time to read of my issue, and thank you in advance for any advice you could give.

THANKS
ANDY

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I had a similar issue with my build - very similar to yours. 00 Silverado, LQ4 370cu, gt45 @ 5psi (will turn up to 10psi today most likely lol), tsp 216/220 .600 cam. I was noticing random KR and it ended up being a bad injector, tested it with a meter and found coil inside was bad. Replaced injector and she was good to go. According to my wideband I only was lean at idle but WOT and cruising it read fine, minus the random KR. Your timing is pretty low for 5psi, at that boost level I am sitting around 20*. If your AFR is good, I would try adding little more timing.

How much timing is it pulling? If it's pulling an even 8* then that seems to be quite common occurrence with the LQ4 as I have read many threads on the subject. I have basically the same setup as you LQ4/4L80, minus the turbo. When I originally swapped the engine I went ahead and changed the knock sensors on spec "since it was already apart". Unfortunately, I purchased cheapo sensors from Ebay. Last summer, I spent a lot of time chasing what seems to be random episodes of the ECM pulling 8* of timing - most often at WOT but not always. On the advice I read on various forums, over the winter, I purchased and installed a set of genuine AC Delco knock sensors but because of this isolation business, I haven't really had a chance to log much lately. I plan on logging some sessions this week and will let you know if this fixed my issue.

The amount of timing being pulled varies. 50% of the time its a deg or less. But other times its all over the board ranging from 3-6 deg, and only once have I seen it go to 8. I had an "issue" right after getting running, where I saw 8 deg of KR consistently... diagnosed that down to the sensors not being plugged in.. haha. Forgot that minor detail when rebuilding my trans over the winter. I cant remember what brand sensors I bought, as it was so long ago, but I do remember they were expensive.