False Knock?

[BrodyO]

Vehicle is a 2005 Chevy Colorado, LY6, Stage 3 Summit Turbo Cam, 7875 Turbo, Currently running speed density while tuning VVE

I'm getting a ton of knock retard on what I consider to already be fairly conservative timing. I'm pretty nice and rich right now (.85-.75 lambda through the pull) running 91 to 93 octane fuel. I can see 12-14 degrees of knock retard throughout the pull netting me negative ignition timing. I'm running about a half a bar of boost currently.

I can try the method of reducing timing 5 degrees below where knock retard is putting me currently (That would be -7 degrees) to see if the KR remains or goes away to help indicate if the knock is false, just seems like a crazy negative number.

Should I have adjusted some knock retard sensitivity value in the calibration after the camshaft swap? Anything else to change/try? Thanks!

[5FDP]

Something is likely rubbing to see that much knock.

[Manny16]

pull the valve cover and check for any failure lifters or rockers

[BrodyO]

Something is likely rubbing to see that much knock.

Can you expand on that a bit for me? Can something like exhaust rubbing on the body cause it or does it need to be something external rubbing on the block? I can check to make sure the knock sensors themselves are still tight.

[blindsquirrel]

The first GM trucks to use a knock sensor were plagued by owner complaints of 'low power, but only when pulling a trailer'. Rattle at the hitch/ball was triggering the sensor and pulling all the timing out. So, anything that the knock sensor is able to 'hear' can set it off.

[BrodyO]

The first GM trucks to use a knock sensor were plagued by owner complaints of 'low power, but only when pulling a trailer'. Rattle at the hitch/ball was triggering the sensor and pulling all the timing out. So, anything that the knock sensor is able to 'hear' can set it off.

Were they able to remedy that issue with any type of knock sensor sensitivity settings? I will go through the truck and take a look by I'm worried I won't find anything.

[blindsquirrel]

This was in the early-mid (? or mid-late?) '80s, when they still had carburetors. Knock sensor only connected to the ESC module in the distributor.

Something clanging around and triggering your knock sensors should really be fixed by eliminating the source of the clanging, not by diddling the tune to try to cover it up.

[BrodyO]

This was in the early-mid (? or mid-late?) '80s, when they still had carburetors. Knock sensor only connected to the ESC module in the distributor.

Something clanging around and triggering your knock sensors should really be fixed by eliminating the source of the clanging, not by diddling the tune to try to cover it up.

Agreed. I'll take a look and report back.

[Alvin]

I've seen excessive KR like this with the knock sensors left loose. There are no pending knock sensor codes?

A log would be better to review than the screen shot.

[blindsquirrel]

Best way for finding rattles I've found is with a rubber mallet. Turn it at an angle so you strike with the corner, it's softer there - if you strike with the flat face it tends to just 'thud' and not do much. Surprising how much of a resonance you can get going on exhaust pipes and suspension parts doing that.