knock issue

[99 gst spyder]

I keep getting knock while in the middle of doing a launch control. I set it to 3.5k and 4.5k and both get knock. Is this something that I should worry about? I'm running e-85. Doesn't get any knock on normal driving and short distant pulls.

In ecmlink, looking at the graph, whats the difference between a long knock vs a knock that spikes? The long knock is more of like a plateau kinda knock and the spike is more like a sharp mountain knock.

Thanks.

 

[DSM1G90]

Simple. You go into a long boost and you in a super rich mode, which creates carbon buildup..and this buildup increases compression ratios...and knocking is the results.

ECU wants to retard spark to prevent knocks from signals by the knock sensor.

Short boosts - doesn't have the time for buildups

Knock is knock, but the spike knocks can blow holes in pistons.

 

[99 gst spyder]

So I shouldn't be doing that since knock is showing?

 

[slo2spool]

How recently have you replaced your knock sensor? A bad knock sensor can cause all sorts of phantom knock. When mine went bad it would sense knock when my open dump wastegate opened.

 

[99 gst spyder]

How recently have you replaced your knock sensor? A bad knock sensor can cause all sorts of phantom knock. When mine went bad it would sense knock when my open dump wastegate opened.

Fairly new knock sensor. And no goo coming out of the back or anything.

 

[slo2spool]

hmm, that's interesting. How much timing are you running at that spot where the knock shows up? You're running e85 so you shouldn't have issues with spark knock like you would with pump gas and it burns much cleaner to so you don't really get carbon deposits but maybe if you just happen to have a boat load of timing you could have issues. But you probably already looked at that.

 

[TeacherCreature]

Check afr at knock spots first if its too lean = heat = preignition = knock
if afr is on point check timing advance if its too high you have same issue causing knock
ive even seen knock from an old mount allowing enough engine shake to cause noise and knock sensor picks that up (for instance exhaust slapping into chasis or something dumb)

 

[DSM1G90]

E85 is nice stuff with 110 plus octane, but it had far less BTU output than does 93 octane due to the alcohol content.

E85 was only intended to make the air cleaner and vehicles producing less junk out the tail pipe.

Thus, takes more E85 to create the same power output with 93, thus a rich mixture is in store to compensate.

Does your car emit the smell of alcohol during idling?

 

[99 gst spyder]

E85 is nice stuff with 110 plus octane, but it had far less BTU output than does 93 octane due to the alcohol content.

E85 was only intended to make the air cleaner and vehicles producing less junk out the tail pipe.

Thus, takes more E85 to create the same power output with 93, thus a rich mixture is in store to compensate.

Does your car emit the smell of alcohol during idling?

I'm not exactly sure what the smell of albohol smells like but I sure can smell some odor out the exhaust pipe. i'll check into the afr's and timing to see where they are too. I'll try to post up a log here.

 

[WES_393]

Simple. You go into a long boost and you in a super rich mode, which creates carbon buildup..and this buildup increases compression ratios...and knocking is the results.

ECU wants to retard spark to prevent knocks from signals by the knock sensor.

Short boosts - doesn't have the time for buildups

I hate to disagree, but there is virtually zero carbon buildup when using E85. The only products from burning Ethanol are Water and CO2. There is a small amount of Carbon produced by the gas mixed into E85, but the rich Ethanol mix and resulting steam take care of that. My piston tops, exhaust ports, manifold, and turbine housing never have more than a light dusting of soot- Likely just from cold starts when Ethanol is too cold to burn properly.


As for knock while using Launch Control, it could just be too much noise from the engine, aka Phantom Knock. The ECU listens to each individual cylinder to get an idea of how much noise they're making (you can see this by logging RawKnock1-4). When one or more cylinders produce a spike of noise louder than the average amount they normally produce, the ECU assumes knock and retards timing. But the noise could be a result of the rev limiter, or high RPM without any load, or something else simple and harmless like that.

So long story short, I wouldn't worry about it. You can try logging the individual RawKnock values to see if one cylinder is way out in left field, but the only time Knock is a huge deal is when the engine is WOT under full load. That's why the knock sensor isn't activated until a certain throttle and RPM point. Otherwise you'd be getting all kinds of pointless CEL's just by cruising through a parking lot.