Spark Knock

[MattD]

Here is just a little info for you guys to consider when seeing knock in your datalogs.

1. You are going to see knock during WOT shifting.

2. You are going to see knock when engine accessories load abruptly increases/decreases (ie ac compressor kicks on/off, etc)

3. You are going to see knock during abrupt throttle changes.

4. You are going to see more knock with high IAT (idle air temeperature) readings than when they are lower.

5. If you are consistently seeing knock at the same rpm in your datalogs, reduce timing by 2 degrees and see if the event changes. If not, then you are probably seeing 'false' knock.

6. False knock is when the knock sensors are 'hearing' knock, but the spark event in the combustion cycle is proper and not causing it.

7. False knock can be caused by many, many things. Engine harmonics and resonance from CAI's and cat-back exhausts are the big causes. Also check to see if your exhaust and/or CAI piping and airbox are rubbing or hitting.

8. Over-fueling can cause knock. Don't guess at this, find someone with a AFR gauge and check this. AFR should be 12.8 - 13.0 during wide open throttle. If your engine is too rich, cylinder wash can occur and if you have actual knock then the combustion can occur below the rings and this will eventually cause premature ring failure.

9. Run the proper weight engine oil or one grade heavier. Too light of an engine oil can cause bearings to vibrate ever so slightly, and guess what, knock sensor can pick it up. This is very rare, especially on newer engines, but can happen.

10. Actual spark knock will eventually hurt your motor. It's just like hitting the top or side of your piston with a hammer during the upstroke. This is very hard on main bearings. First sign will be oil consumption and then bearing failure.

[Mike_Levy]

Great Post!!! Accurate for the most part but not completely. Some of it only applies to the Hemis and other Speed Density motors, like the abrupt throttle changes. Mass Air motors will sense the extra air and adjust before they knock. Thats something I used to see all the time with my Hemis, but never with my LS motors. Same thing for the accessories. Rarely see it on the LS's. Something else that should be noted, Lugging the motor, will cause it to knock excessively. When you don't give it enough throttle to make it kick down, but you're trying to accelerate, thats murder on it.

EDIT: Oops, this is the Dodge board. LS's are irrelevant.

[stealth300c]

My hemi is at 14.71 afr at 2150 rpm and stays there when Im doing a steady 70 on the highway is this normal? LT knock doesn't move WOT or steady throttle. pulled 4 degrees ST knock should I retard the timing by 2 degrees or 4? I am starting to learn this whole tuning thing and enjoy learning it. any input is much appreciated. my fuel is all over the place after I let off the throttle. 1/1 short term ADAP and 2/1 long term ADAP is really up and down thanks in advance.