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?