Engine Knock

[EricS09RA]

I did some logging with evoscan yesterday. My first pull showed engine knock throughout the entire pull. It spiked as high as 8, and held at 2-3 for most of the run. I did 5 more pulls after that. Some showed 0 knock, others showed a small spike at the beginning of the run, then it went right back to 0. what would cause so much knock on the first run, then 0 immediately after? How concerned should I be?

[wutangmo15]

Knock on the first run is pretty normal. After that, as long as the knock is random and under 5, then it will be fine. The problem occurs when you have knock at the same location every time, that's when you'll need to tune it out.

[EricS09RA]

on the other runs that showed knock, it was always at the very begining of the pull. I think the knock count was 2 on 2 of the runs then on the last pull it spiked to five at the begining.

[MikeW-RRE]

You need less ignition advance in those spots or more fuel or both. When it was tuned it may not have hit those load cells. Or if untuned your mods are too much confusion for the ECU. 1-3 counts here and there and random is normal. For a tuned car or a stock car even. 8 counts and consistent needs attention.

Mike W

[BravoZero]

Question...

How long can an engine withstand constant knocking before it starts having major issues?

[EricS09RA]

I was tuned, but I believe he only tuned in 3rd gear. I did 3 pulls in 4th and 3 in 5th gear. The pull that showed knock all the way across was in 5th.

[MikeW-RRE]

Question...

How long can an engine withstand constant knocking before it starts having major issues?

Dunno. How many red lights can you run through before you have major issues? I dont think there is a specific number. Could be one. Could be 100.

Mike W

[hackerrei]

Here some info I got about knock from John COBBs EVO calibrator hope it will help you.

Dont worry about intermittent knock below 3-4 unless its in the same place every time even then the knock sensor on these cars is really sensitive and just doing its job by removing one degree of timing to combat it

1. Knock that appears to be random/non-repeatable and less than 3.
This type of knock you can usually ignore. It typically means your spark map is a
good match for the fuel/boost/modifications that you are currently running.

2. Knock at part throttle, starting at less than 3500rpm.
This type of knock can be caused by many factors, many of which are effectively
“False Knock”, though each will require a specific remedy.

2.1 Low octane fuel, the knock is real, get the correct octane fuel and tune as per
WOT knock tuning.

2.2 Noisy engine/driveline components:
Valve-lash adjusters - These can and should be replaced if they are the problem.
Use electronic DET-CANS to diagnose the problem.
Plumbing rattles - Intercooler, exhaust or whatever. This is the knock sensor
picking up loud engine noise and will require fixing the mechanical fault These can
be somewhat harder to find sometimes. Use electronic DET-CANS to help diagnose
the problem.
Forged pistons and piston slap - Some combinations cause a problem, others don’t.
This is a tough one, short of changing the pistons, it is better to fix with the ECU,
see the FALSE KNOCK section. Note that you can hear piston slap with good
electronic DET-CANS.
Balance shafts removed - Affects some cars, not others. Fix via the ECU, see the
FALSE KNOCK section.
Clutch rattle - Some twin-plate clutches have been reported as causing a problem
and can be difficult to diagnose. Use electronic DET-CANS to help diagnose the
problem. Fix via the ECU, see the FALSE KNOCK section.


3. Knock at WOT not associated with a gear change.
This is generally real knock or detonation and will respond to reducing the ignition
timing and/or using a fuel with a higher octane rating or AKI.
This type of knock we tune out by adjusting the HI-OCTANE SPARK MAP.

See DEALING WITH WOT KNOCK.
It is best to first check that the knock is directly related to the spark map by
lowering the whole spark map above Load 100 by 6° and re logging. If the knock
disappears, or is much reduced, the spark map will require tuning. If the knock
remains much as it was, then the problem is not the spark map.
Light-tune engines having to run on low octane fuel will benefit from reducing the
timing of the cells where knock occurs until it is eliminated. If you regularly have to
use low octane fuel, look into using one of the tephra ROMs with alternate
mapping. These can be setup to accommodate switching between good and poor
fuel. They can also be used to switch between gasoline fuel and ethanol fuel.

4. Knock at WOT that is associated with a gear change.
This type of knock can be tricky to eliminate without sacrificing an otherwise good
spark map.


Search for merlins tuning Guide ^^