Knock retard driving me crazy

[boogsawaste]

Long story short I have been battling knock retard for a bit now. Usually in the 2,800-4,000rpm range around .52 grams cylinder airmass (give or take). Other times it will be clean up until redline. I have been pulling timing from those areas and more to see if I get any changes and as soon as I think I do it'll pull timing again. I'm not sure if it's false or real KR. My car is a 2000 corvette that has headers, high flow catted mid pipe, borla s type axle back, breathless cold air, summit 8720 cam (same as the "high lift hotcam"). I also 6 speed swapped the car and have been fighting the speed reading correctly in the VCM scanner which is why it's not set in MPH. It's the closest I can get to actual MPH so I have a reference as to what gear I'm in. Speedometer in car reads correctly and checked against GPS. If anyone knows how to fix that I'd appreciate it as I've messed with the gear calculator and numbers in the speedo correction to no end.

Anyway back to the knock retard. Anyone have any pointers? should I load something like a stock truck timing table which has drastically lower timing than I have loaded now? Just to see if it indeed is real or false KR? Anyone see anything way off base with my tune? I'm about to load stock VE table and start over. THANK YOU TO ANYONE giving any advice no matter how big or small.

Scans are 2 with KR and 2 without. I should have some more scans after I pulled even more timing with the same or worse results that I can upload if needed.

[Alvin]

If it won't go away with pulling timing in that particular spot check for things banging or making noise. Engine noises can cause this. Also as knock sensors age they either pick up every little irrelevant noise or nothing at all. This could be knock sensors going bad too.

I had a newer GEN5 truck that was fighting me with knock. Engine sounded quiet until I pulled it up on a set of ramps for something else.. Foot braking this thing would make a knock in the engine. That was setting off the knock sensors.

First step is just to see if removing timing gets rid of it.

[boogsawaste]

Thanks Alvin! I?ll pull a bunch of timing in those areas and see if nothing changes. I?ve been dropping 2? a time but I think I need to go more drastic. If it doesn?t help I?ll have to start digging into something banging or the sensors themselves. Appreciate it!

[gtstorey]

You could also increase octane and see if it reduces knock.

[boogsawaste]

You could also increase octane and see if it reduces knock.

Good suggestion. I’m running 93 which is the highest locally. If there’s an octane booster that actually does something I’d give it a try.

[gametech]

Good suggestion. I’m running 93 which is the highest locally. If there’s an octane booster that actually does something I’d give it a try.

Don't be afraid to just cut 5 or 10 degrees off everything but your idle spark as a test. If you still show knock retard, you know you have a mechanical noise problem. Just don't drive around like that any longer than a short test run requires.

[boogsawaste]

Don't be afraid to just cut 5 or 10 degrees off everything but your idle spark as a test. If you still show knock retard, you know you have a mechanical noise problem. Just don't drive around like that any longer than a short test run requires.

I pulled 13 or so in those areas from the stock tune closely mimicking a stock 01 Tahoe tune made to run on 87. If it’s still knocking at that point it’s definitely false. I did find that my DIY PCV tube fittings were hitting and rattling in a few places so I secured those better now. I know, I know, change one thing at a time but I’m a bit OCD and if I don’t get any knock changing the timing and securing the brass fittings in that line then I’ll start adding timing back in those areas and keep my eyes on it. It’s been raining like crazy here so not gonna get a chance to lay into it much in the next few days but will at some point and I’ll report back. Edit: I didn’t only focus on the problem area. I went from stock 28? max to 22 at the top end. Idle is stock and is working good with this cam so I left that alone.

Side note does anyone have any ideas about why my scanner mph is more than double off compared to what my gauge is reading?

[Alvin]

likely kmh to mph for your gauges.

[boogsawaste]

likely kmh to mph for your gauges.

Unfortunately I’ve tried to set it to mph, kmh, and even knots lol. Nothing is accurate. It’s strange though because the actual dash gauge is correct. It wasn’t after the manual trans swap but I forget what setting I messed with to correct it though. Since that swap the vcm reading is about double though leading me to believe the same as you as far as kmh. It’s not the end of the world as meters per second gets me ballpark at least. Maybe I should try deleting and re installing the scanner and see if that fixes it.

[boogsawaste]

Ok had some time to play with timing and take some scans. First off I kept taking timing away and still having KR showing in the scans. I pulled a LOT of timing by the end to the point that the car was a major turd and still seeing KR. I looked over and over looking for something that could be banging around that I can't hear and tied up all I could. Nothing seemed majorly out of place or able to cause false knock so I'm not sure with all of that short of maybe some drivetrain noise or similar that I cannot hear myself. Finally I loaded my normal tune back on and scanned with pretty much no KR at all. I thought I must have tied back something rattling or whatever. Scanned again today and that random KR re appeared! Then just like that it's gone again at the same cells in the scanner. Not getting any major wheelspin. I'm pretty sure that it's false as my car is just bolt on and a milder summit cam (218/227 .600/.600). The tune is nothing wild and it's basically stock timing with 4* pulled after 3200rpm. These old LS1's have some crazy stock timing it appears. This KR seems to have appeared sometime after the cam swap and my valvetrain is a bit noisier than stock. I've heard these summit cams have some aggressive lobes so they can be noisy along with my headers having amplified all the noise. Would it be unwise to assume at this point it's false? Possibly copy the 01+ c5 knock sensor settings which seem to be a little milder? I'll put up some scans and the final low timing tune that was still showing KR.

Order of attachments:

Low timing tune
Scan with low timing tune and still getting KR
The tune that's loaded on the car with almost all stock 00 C5 timing
Scan from today with a pretty decent amount of KR
Scan from 7-17 with current tune and hardly KR in the normal area
Scan from today, same time as the one with KR but hardly KR

I have some other short scans where I'm doing just a quick run over the range I was seeing KR. Nothing long but I can add any channels or take more logs if anything is needed. Driving me nuts!