Knock that won't go away
10-19-2021, 02:44 PM
#1
Knock that won't go away Trying to get my truck tuned up to where I can at least drive it when needed (deer season!), will be a bit before I make it in for a dyno tune. Stage 2 cam, rebuilt bottom end, stock heads with a valve job. Starts idles and runs fine, no missing or obvious issues, but I keep having random knock that I can't get to go away. I've took out timing multiple times and it seemed to not change anything, so I even flashed the stock timing tables back in it and it still is doing the same thing. I'm not sure if maybe my knock sensors are picking up something they shouldn't or what the issue is. It seems to knock reliably when you first put the gas to it, before the rpms start rising. I would call it "tip in" but not sure if that's actually going to be called "tip in knock". Also at random times, usually after making a stop and letting the truck sit for 10-15 mins, when I start up and take off again, I get pretty big bursts of knock at random spots, that don't seem to replicate each time I'm in those cells. Think dialing in the fueling first would address some of this knock or do you think something else is going on? There's no audible knock and no I don't have any way to verify it's actually knock outside of my stock knock sensors currently. Thanks for any help!
10-22-2021, 05:35 AM
#2
TECH Fanatic
I’m on my phone, so I can’t see the files, BUT, I’ll say knock can be a lot of things. First make sure you don’t have any metal on metal contact anywhere. Typically this is the exhaust. The sensors are just microphones which listen for metal on metal frequencies.
Next, turn off burst knock if you haven’t already. It’s predictive, not real.
Check your AFR’s, and yes a bad mix can cause it. Fatten it up and see if it’s still unresponsive.
If it’s not solved now, and timing or AFR won’t fix it, it may be picking up other engine noises like valvetrain. In this is the case, you need to tune the sensors. Do this by getting some race gas like 110, and reduce sensitivity until it stops registering. Verify they still work by tapping the block or exhaust manifold with a wrench. They should pick up the sound.
If I get a chance later I’ll take a look at the files. Real knock looks like a staircase, and false is just a spike in the scanner. Real knock doesn’t solve itself, which is why it tends to come in worse on the next cycle. If left unchecked it would continue to “step up” and like I said it resembles a staircase.
Next, turn off burst knock if you haven’t already. It’s predictive, not real.
Check your AFR’s, and yes a bad mix can cause it. Fatten it up and see if it’s still unresponsive.
If it’s not solved now, and timing or AFR won’t fix it, it may be picking up other engine noises like valvetrain. In this is the case, you need to tune the sensors. Do this by getting some race gas like 110, and reduce sensitivity until it stops registering. Verify they still work by tapping the block or exhaust manifold with a wrench. They should pick up the sound.
If I get a chance later I’ll take a look at the files. Real knock looks like a staircase, and false is just a spike in the scanner. Real knock doesn’t solve itself, which is why it tends to come in worse on the next cycle. If left unchecked it would continue to “step up” and like I said it resembles a staircase.
10-23-2021, 01:10 AM
#4
Just a bit more info on this. The trucks have very aggressive burst knock settings. I fully agree with the idea of killing that table as a diagnostic means of determining real knock, but you may wish to enable it again after you have finished tuning, although perhaps with modifications.
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